capnpc/

codegen.rs

// Copyright (c) 2013-2015 Sandstorm Development Group, Inc. and contributors
// Licensed under the MIT License:
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

use std::collections;
use std::collections::{HashMap, HashSet};
use std::path::{Path, PathBuf};

use capnp::schema_capnp;
use capnp::Error;

use self::FormattedText::{BlankLine, Branch, Indent, Line};
use crate::codegen_types::{do_branding, Leaf, RustNodeInfo, RustTypeInfo, TypeParameterTexts};
use crate::convert_io_err;
use crate::pointer_constants::generate_pointer_constant;

/// An invocation of the capnpc-rust code generation plugin.
pub struct CodeGenerationCommand {
    output_directory: PathBuf,
    default_parent_module: Vec<String>,
    raw_code_generator_request_path: Option<PathBuf>,
    capnp_root: String,
    crates_provide_map: HashMap<u64, String>,
}

impl Default for CodeGenerationCommand {
    fn default() -> Self {
        Self {
            output_directory: PathBuf::new(),
            default_parent_module: Vec::new(),
            raw_code_generator_request_path: None,
            capnp_root: "::capnp".into(),
            crates_provide_map: HashMap::new(),
        }
    }
}

impl CodeGenerationCommand {
    /// Creates a new code generation command with default options.
    pub fn new() -> Self {
        Self::default()
    }

    /// Sets the output directory.
    pub fn output_directory<P>(&mut self, path: P) -> &mut Self
    where
        P: AsRef<Path>,
    {
        self.output_directory = path.as_ref().to_path_buf();
        self
    }

    /// Sets the default parent module, indicating the scope in your crate where you will
    /// add the generated code.
    ///
    /// This option can be overridden by the `parentModule` annotation defined in `rust.capnp`.
    pub fn default_parent_module(&mut self, default_parent_module: Vec<String>) -> &mut Self {
        self.default_parent_module = default_parent_module;
        self
    }

    /// Sets the root path for referencing things in the `capnp` crate from the generated
    /// code. Usually this is `::capnp`. When we bootstrap schema.capnp we set this to `crate`.
    /// If you are renaming the `capnp` crate when importing it, then you probably want to set
    /// this value.
    pub fn capnp_root(&mut self, capnp_root: &str) -> &mut Self {
        self.capnp_root = capnp_root.into();
        self
    }

    /// Sets the raw code generator request output path.
    pub fn raw_code_generator_request_path<P>(&mut self, path: P) -> &mut Self
    where
        P: AsRef<Path>,
    {
        self.raw_code_generator_request_path = Some(path.as_ref().to_path_buf());
        self
    }

    /// Sets the crate provides map.
    ///
    /// # Arguments
    ///
    /// - `map` - A map from capnp file id to the crate name that provides the
    ///   corresponding generated code.
    ///
    /// See [`crate::CompilerCommand::crate_provides`] for more details.
    pub fn crates_provide_map(&mut self, map: HashMap<u64, String>) -> &mut Self {
        self.crates_provide_map = map;
        self
    }

    /// Generates Rust code according to a `schema_capnp::code_generator_request` read from `inp`.
    pub fn run<T>(&mut self, inp: T) -> ::capnp::Result<()>
    where
        T: std::io::Read,
    {
        use capnp::serialize;
        use std::io::Write;

        let message = serialize::read_message(inp, capnp::message::ReaderOptions::new())?;

        let ctx = GeneratorContext::new_from_code_generation_command(self, &message)?;

        for requested_file in ctx.request.get_requested_files()? {
            let id = requested_file.get_id();
            let mut filepath = self.output_directory.to_path_buf();
            let requested = ::std::path::PathBuf::from(requested_file.get_filename()?.to_str()?);
            filepath.push(requested);
            if let Some(parent) = filepath.parent() {
                ::std::fs::create_dir_all(parent).map_err(convert_io_err)?;
            }

            let root_name = path_to_stem_string(&filepath)?.replace('-', "_");
            filepath.set_file_name(format!("{root_name}_capnp.rs"));

            let capnp_version = match ctx.request.get_capnp_version() {
                Ok(version) => format!(
                    "{}.{}.{}",
                    version.get_major(),
                    version.get_minor(),
                    version.get_micro()
                ),
                Err(_) => "<unknown>".to_owned(),
            };

            let lines =
                Branch(vec![
                Line(
                    "// @generated by the capnpc-rust plugin to the Cap'n Proto schema compiler."
                        .to_string(),
                ),
                line("// DO NOT EDIT."),
                Line(format!("// source: {}", requested_file.get_filename()?.to_str()?)),
                Line(format!("// capnp binary version: {}", capnp_version)),
                Line(format!("// capnpc crate version: {}", env!("CARGO_PKG_VERSION"))),
                BlankLine,
                generate_node(&ctx, id, &root_name)?,
            ]);

            let text = stringify(&lines);

            let previous_text = ::std::fs::read(&filepath);
            if previous_text.is_ok() && previous_text.unwrap() == text.as_bytes() {
                // File is unchanged. Do not write it so that builds with the
                // output as part of the source work in read-only filesystems
                // and so timestamp-based build systems and watchers do not get
                // confused.
                continue;
            }

            // It would be simpler to use the ? operator instead of a pattern match, but then the error message
            // would not include `filepath`.
            match ::std::fs::File::create(&filepath) {
                Ok(mut writer) => {
                    writer.write_all(text.as_bytes()).map_err(convert_io_err)?;
                }
                Err(e) => {
                    let _ = writeln!(
                        &mut ::std::io::stderr(),
                        "could not open file {filepath:?} for writing: {e}"
                    );
                    return Err(convert_io_err(e));
                }
            }
        }

        if let Some(raw_code_generator_request) = &self.raw_code_generator_request_path {
            let raw_code_generator_request_file =
                ::std::fs::File::create(raw_code_generator_request).map_err(convert_io_err)?;
            serialize::write_message_segments(
                raw_code_generator_request_file,
                &message.into_segments(),
            )?;
        }

        Ok(())
    }
}

pub struct GeneratorContext<'a> {
    pub request: schema_capnp::code_generator_request::Reader<'a>,
    pub node_map: collections::hash_map::HashMap<u64, schema_capnp::node::Reader<'a>>,
    pub scope_map: collections::hash_map::HashMap<u64, Vec<String>>,

    /// Map from node ID to the node ID of its parent scope. This is equal to node.scope_id
    /// for all nodes except for autogenerated interface Param and Result structs;
    /// those have scope_id set to 0. See the comment on paramStructType in schema.capnp.
    pub node_parents: collections::hash_map::HashMap<u64, u64>,

    /// Root path for referencing things in the `capnp` crate from the generated code.
    pub capnp_root: String,
}

impl<'a> GeneratorContext<'a> {
    pub fn new(
        message: &'a capnp::message::Reader<capnp::serialize::OwnedSegments>,
    ) -> ::capnp::Result<GeneratorContext<'a>> {
        GeneratorContext::new_from_code_generation_command(&Default::default(), message)
    }

    fn new_from_code_generation_command(
        code_generation_command: &CodeGenerationCommand,
        message: &'a capnp::message::Reader<capnp::serialize::OwnedSegments>,
    ) -> ::capnp::Result<GeneratorContext<'a>> {
        let mut default_parent_module_scope = vec!["crate".to_string()];
        default_parent_module_scope
            .extend_from_slice(&code_generation_command.default_parent_module[..]);

        let mut ctx = GeneratorContext {
            request: message.get_root()?,
            node_map: collections::hash_map::HashMap::<u64, schema_capnp::node::Reader<'a>>::new(),
            scope_map: collections::hash_map::HashMap::<u64, Vec<String>>::new(),
            node_parents: collections::hash_map::HashMap::new(),
            capnp_root: code_generation_command.capnp_root.clone(),
        };

        let crates_provide = &code_generation_command.crates_provide_map;

        for node in ctx.request.get_nodes()? {
            ctx.node_map.insert(node.get_id(), node);
            ctx.node_parents.insert(node.get_id(), node.get_scope_id());
        }

        // Fix up "anonymous" method params and results scopes.
        for node in ctx.request.get_nodes()? {
            if let Ok(schema_capnp::node::Interface(interface_reader)) = node.which() {
                for method in interface_reader.get_methods()? {
                    let param_struct_type = method.get_param_struct_type();
                    if ctx.node_parents.get(&param_struct_type) == Some(&0) {
                        ctx.node_parents.insert(param_struct_type, node.get_id());
                    }
                    let result_struct_type = method.get_result_struct_type();
                    if ctx.node_parents.get(&result_struct_type) == Some(&0) {
                        ctx.node_parents.insert(result_struct_type, node.get_id());
                    }
                }
            }
        }

        for requested_file in ctx.request.get_requested_files()? {
            let id = requested_file.get_id();

            for import in requested_file.get_imports()? {
                let importpath = ::std::path::Path::new(import.get_name()?.to_str()?);
                let root_name: String = format!(
                    "{}_capnp",
                    path_to_stem_string(importpath)?.replace('-', "_")
                );
                let parent_module_scope = if let Some(krate) = crates_provide.get(&import.get_id())
                {
                    vec![format!("::{krate}")]
                } else {
                    default_parent_module_scope.clone()
                };

                ctx.populate_scope_map(
                    parent_module_scope,
                    root_name,
                    NameKind::Verbatim,
                    import.get_id(),
                )?;
            }

            let root_name = path_to_stem_string(requested_file.get_filename()?.to_str()?)?;
            let root_mod = format!("{}_capnp", root_name.replace('-', "_"));
            ctx.populate_scope_map(
                default_parent_module_scope.clone(),
                root_mod,
                NameKind::Verbatim,
                id,
            )?;
        }
        Ok(ctx)
    }

    fn get_last_name(&self, id: u64) -> ::capnp::Result<&str> {
        match self.scope_map.get(&id) {
            None => Err(Error::failed(format!("node not found: {id}"))),
            Some(v) => match v.last() {
                None => Err(Error::failed(format!("node has no scope: {id}"))),
                Some(n) => Ok(n),
            },
        }
    }

    fn populate_scope_map(
        &mut self,
        mut ancestor_scope_names: Vec<String>,
        mut current_node_name: String,
        current_name_kind: NameKind,
        node_id: u64,
    ) -> ::capnp::Result<()> {
        // unused nodes in imported files might be omitted from the node map
        let Some(&node_reader) = self.node_map.get(&node_id) else {
            return Ok(());
        };

        for annotation in node_reader.get_annotations()? {
            if annotation.get_id() == NAME_ANNOTATION_ID {
                current_node_name = name_annotation_value(annotation)?.to_string();
            } else if annotation.get_id() == PARENT_MODULE_ANNOTATION_ID {
                let head = ancestor_scope_names[0].clone();
                ancestor_scope_names.clear();
                ancestor_scope_names.push(head);
                ancestor_scope_names.append(&mut get_parent_module(annotation)?);
            }
        }

        let mut scope_names = ancestor_scope_names;
        scope_names.push(capnp_name_to_rust_name(
            &current_node_name,
            current_name_kind,
        ));

        self.scope_map.insert(node_id, scope_names.clone());

        let nested_nodes = node_reader.get_nested_nodes()?;
        for nested_node in nested_nodes {
            let nested_node_id = nested_node.get_id();
            match self.node_map.get(&nested_node_id) {
                None => {}
                Some(node_reader) => match node_reader.which() {
                    Ok(schema_capnp::node::Enum(_enum_reader)) => {
                        self.populate_scope_map(
                            scope_names.clone(),
                            nested_node.get_name()?.to_string()?,
                            NameKind::Verbatim,
                            nested_node_id,
                        )?;
                    }
                    _ => {
                        self.populate_scope_map(
                            scope_names.clone(),
                            nested_node.get_name()?.to_string()?,
                            NameKind::Module,
                            nested_node_id,
                        )?;
                    }
                },
            }
        }

        if let Ok(schema_capnp::node::Struct(struct_reader)) = node_reader.which() {
            let fields = struct_reader.get_fields()?;
            for field in fields {
                if let Ok(schema_capnp::field::Group(group)) = field.which() {
                    self.populate_scope_map(
                        scope_names.clone(),
                        get_field_name(field)?.to_string(),
                        NameKind::Module,
                        group.get_type_id(),
                    )?;
                }
            }
        }

        Ok(())
    }

    pub fn get_qualified_module(&self, type_id: u64) -> String {
        self.scope_map[&type_id].join("::")
    }
}

/// Like `format!(...)`, but adds a `capnp=ctx.capnp_root` argument.
macro_rules! fmt(
    ($ctx:ident, $($arg:tt)*) => ( format!($($arg)*, capnp=$ctx.capnp_root) )
);

pub(crate) use fmt;

fn path_to_stem_string<P: AsRef<::std::path::Path>>(path: P) -> ::capnp::Result<String> {
    if let Some(stem) = path.as_ref().file_stem() {
        stem.to_owned()
            .into_string()
            .map_err(|os_string| Error::failed(format!("bad filename: {os_string:?}")))
    } else {
        Err(Error::failed(format!(
            "file has no stem: {:?}",
            path.as_ref()
        )))
    }
}

fn camel_to_snake_case(s: &str) -> String {
    let mut result_chars: Vec<char> = Vec::new();
    let mut first_char = true;
    for c in s.chars() {
        if c.is_uppercase() && !first_char {
            result_chars.push('_');
        }
        result_chars.push(c.to_ascii_lowercase());
        first_char = false;
    }
    result_chars.into_iter().collect()
}

fn capitalize_first_letter(s: &str) -> String {
    let mut result_chars: Vec<char> = Vec::new();
    for c in s.chars() {
        result_chars.push(c)
    }
    result_chars[0] = result_chars[0].to_ascii_uppercase();
    result_chars.into_iter().collect()
}

/// Formats a u64 into a string representation of the hex value, with
/// separating underscores. Used instead of simple hex formatting to prevent
/// clippy warnings in autogenerated code. This is loosely based off of
/// similar functionality in the `separator` crate.
fn format_u64(value: u64) -> String {
    let hex = format!("{value:#x}");
    let mut separated = hex[0..2].to_string();
    let mut place = hex.len() - 2;
    let mut later_loop = false;

    for ch in hex[2..].chars() {
        if later_loop && place % 4 == 0 {
            separated.push('_');
        }

        separated.push(ch);
        later_loop = true;
        place -= 1;
    }

    separated
}

#[test]
fn test_camel_to_snake_case() {
    assert_eq!(camel_to_snake_case("fooBar"), "foo_bar".to_string());
    assert_eq!(camel_to_snake_case("FooBar"), "foo_bar".to_string());
    assert_eq!(camel_to_snake_case("fooBarBaz"), "foo_bar_baz".to_string());
    assert_eq!(camel_to_snake_case("FooBarBaz"), "foo_bar_baz".to_string());
    assert_eq!(camel_to_snake_case("helloWorld"), "hello_world".to_string());
    assert_eq!(camel_to_snake_case("HelloWorld"), "hello_world".to_string());
    assert_eq!(camel_to_snake_case("uint32Id"), "uint32_id".to_string());

    assert_eq!(camel_to_snake_case("fooBar_"), "foo_bar_".to_string());
}

#[derive(PartialEq, Clone)]
pub enum FormattedText {
    Indent(Box<FormattedText>),
    Branch(Vec<FormattedText>),
    Line(String),
    BlankLine,
}

impl From<Vec<FormattedText>> for FormattedText {
    fn from(value: Vec<FormattedText>) -> Self {
        Branch(value)
    }
}

pub fn indent(inner: impl Into<FormattedText>) -> FormattedText {
    Indent(Box::new(inner.into()))
}

pub fn line(inner: impl ToString) -> FormattedText {
    Line(inner.to_string())
}

fn to_lines(ft: &FormattedText, indent: usize) -> Vec<String> {
    match ft {
        Indent(ft) => to_lines(ft, indent + 1),
        Branch(fts) => fts.iter().flat_map(|ft| to_lines(ft, indent)).collect(),
        Line(s) => {
            let mut s1: String = " ".repeat(indent * 4);
            s1.push_str(s);
            vec![s1.to_string()]
        }
        BlankLine => vec!["".to_string()],
    }
}

fn stringify(ft: &FormattedText) -> String {
    let mut result = to_lines(ft, 0).join("\n");
    result.push('\n');
    result
}

const RUST_KEYWORDS: &[&str] = &[
    "abstract", "alignof", "as", "be", "become", "box", "break", "const", "continue", "crate",
    "do", "else", "enum", "extern", "false", "final", "fn", "for", "if", "impl", "in", "let",
    "loop", "macro", "match", "mod", "move", "mut", "offsetof", "once", "override", "priv", "proc",
    "pub", "pure", "ref", "return", "self", "sizeof", "static", "struct", "super", "trait", "true",
    "type", "typeof", "unsafe", "unsized", "use", "virtual", "where", "while", "yield",
];

fn module_name(camel_case: &str) -> String {
    let mut name = camel_to_snake_case(camel_case);
    if RUST_KEYWORDS.contains(&&*name) {
        name.push('_');
    }
    name
}

// Annotation IDs, as defined in rust.capnp.
const NAME_ANNOTATION_ID: u64 = 0xc2fe4c6d100166d0;
const PARENT_MODULE_ANNOTATION_ID: u64 = 0xabee386cd1450364;
const OPTION_ANNOTATION_ID: u64 = 0xabfef22c4ee1964e;

// StreamResult type ID, as defined in stream.capnp.
const STREAM_RESULT_ID: u64 = 0x995f9a3377c0b16e;

fn name_annotation_value(annotation: schema_capnp::annotation::Reader<'_>) -> capnp::Result<&str> {
    if let schema_capnp::value::Text(t) = annotation.get_value()?.which()? {
        let name = t?.to_str()?;
        for c in name.chars() {
            if !(c == '_' || c.is_alphanumeric()) {
                return Err(capnp::Error::failed(
                    "rust.name annotation value must only contain alphanumeric characters and '_'"
                        .to_string(),
                ));
            }
        }
        Ok(name)
    } else {
        Err(capnp::Error::failed(
            "expected rust.name annotation value to be of type Text".to_string(),
        ))
    }
}

fn get_field_name(field: schema_capnp::field::Reader<'_>) -> capnp::Result<&str> {
    for annotation in field.get_annotations()? {
        if annotation.get_id() == NAME_ANNOTATION_ID {
            return name_annotation_value(annotation);
        }
    }
    Ok(field.get_name()?.to_str()?)
}

fn get_enumerant_name(enumerant: schema_capnp::enumerant::Reader<'_>) -> capnp::Result<&str> {
    for annotation in enumerant.get_annotations()? {
        if annotation.get_id() == NAME_ANNOTATION_ID {
            return name_annotation_value(annotation);
        }
    }
    Ok(enumerant.get_name()?.to_str()?)
}

fn get_parent_module(annotation: schema_capnp::annotation::Reader) -> capnp::Result<Vec<String>> {
    if let schema_capnp::value::Text(t) = annotation.get_value()?.which()? {
        let module = t?.to_str()?;
        Ok(module.split("::").map(|x| x.to_string()).collect())
    } else {
        Err(capnp::Error::failed(
            "expected rust.parentModule annotation value to be of type Text".to_string(),
        ))
    }
}
#[derive(Clone, Copy)]
enum NameKind {
    // convert camel case to snake case, and avoid Rust keywords
    Module,

    // don't modify
    Verbatim,
}

fn capnp_name_to_rust_name(capnp_name: &str, name_kind: NameKind) -> String {
    match name_kind {
        NameKind::Module => module_name(capnp_name),
        NameKind::Verbatim => capnp_name.to_string(),
    }
}

fn is_option_field(field: schema_capnp::field::Reader) -> capnp::Result<bool> {
    use capnp::schema_capnp::*;

    let enabled = field
        .get_annotations()?
        .iter()
        .any(|a| a.get_id() == OPTION_ANNOTATION_ID);

    if enabled {
        let supported = match field.which()? {
            field::Which::Group(_) => false,
            field::Which::Slot(field) => {
                let ty = field.get_type()?;
                ty.is_pointer()? && !matches!(ty.which()?, type_::Interface(_))
            }
        };
        if !supported {
            return Err(capnp::Error::failed(
                "$Rust.option annotation only supported on pointer fields (support for optional interfaces isn't implemented yet)".to_string(),
            ));
        }
    }

    Ok(enabled)
}

fn prim_default(value: &schema_capnp::value::Reader) -> ::capnp::Result<Option<String>> {
    use capnp::schema_capnp::value;
    match value.which()? {
        value::Bool(false)
        | value::Int8(0)
        | value::Int16(0)
        | value::Int32(0)
        | value::Int64(0)
        | value::Uint8(0)
        | value::Uint16(0)
        | value::Uint32(0)
        | value::Uint64(0) => Ok(None),

        value::Bool(true) => Ok(Some("true".to_string())),
        value::Int8(i) => Ok(Some(i.to_string())),
        value::Int16(i) => Ok(Some(i.to_string())),
        value::Int32(i) => Ok(Some(i.to_string())),
        value::Int64(i) => Ok(Some(i.to_string())),
        value::Uint8(i) => Ok(Some(i.to_string())),
        value::Uint16(i) => Ok(Some(i.to_string())),
        value::Uint32(i) => Ok(Some(i.to_string())),
        value::Uint64(i) => Ok(Some(i.to_string())),
        value::Float32(f) => match f.classify() {
            ::std::num::FpCategory::Zero => Ok(None),
            _ => Ok(Some(format!("{}u32", f.to_bits()))),
        },
        value::Float64(f) => match f.classify() {
            ::std::num::FpCategory::Zero => Ok(None),
            _ => Ok(Some(format!("{}u64", f.to_bits()))),
        },
        _ => Err(Error::failed(
            "Non-primitive value found where primitive was expected.".to_string(),
        )),
    }
}

// A primitive default *value* (not the mask) as a Rust expression, in the context of the field's
// type. Used for the unmapped-leaf read in the erased carrier: an unmapped `@[...]` leaf reads its
// default (matching C++'s `unmask<T>(0, mask)`), and the sentinel offset must not be dereferenced.
fn prim_default_value(value: &schema_capnp::value::Reader) -> ::capnp::Result<String> {
    use capnp::schema_capnp::value;
    Ok(match value.which()? {
        value::Bool(b) => b.to_string(),
        value::Int8(i) => i.to_string(),
        value::Int16(i) => i.to_string(),
        value::Int32(i) => i.to_string(),
        value::Int64(i) => i.to_string(),
        value::Uint8(i) => i.to_string(),
        value::Uint16(i) => i.to_string(),
        value::Uint32(i) => i.to_string(),
        value::Uint64(i) => i.to_string(),
        value::Float32(f) => format!("f32::from_bits({}u32)", f.to_bits()),
        value::Float64(f) => format!("f64::from_bits({}u64)", f.to_bits()),
        _ => {
            return Err(Error::failed(
                "expected a primitive default value".to_string(),
            ))
        }
    })
}

// True if a field is a scalar data field (read via `get_data_field`): a bool or fixed-width
// integer/float. Such an accessor needs an explicit sentinel guard for an unmapped leaf, because
// the out-of-range offset would overflow the bounds check on a 32-bit target. Pointer reads are
// naturally safe (an out-of-range pointer index returns a null/default reader).
fn is_scalar_data_field(field: &schema_capnp::field::Reader) -> ::capnp::Result<bool> {
    use capnp::schema_capnp::*;
    let field::Slot(s) = field.which()? else {
        return Ok(false);
    };
    Ok(matches!(
        s.get_type()?.which()?,
        type_::Bool(())
            | type_::Int8(())
            | type_::Int16(())
            | type_::Int32(())
            | type_::Int64(())
            | type_::Uint8(())
            | type_::Uint16(())
            | type_::Uint32(())
            | type_::Uint64(())
            | type_::Float32(())
            | type_::Float64(())
    ))
}

// Sentinel guard for an erased *builder* mutator writing at leaf `idx`: panic if the leaf is
// unmapped (matching C++'s `KJ_REQUIRE`). The builder's raw writes are not bounds-checked, so
// without this an unmapped `@[...]` set would be UB rather than a clean error.
fn unmapped_panic(idx: usize, field_name: &str) -> String {
    format!(
        "if self.offsets[{idx}] == 0xffff_ffffu32 {{ panic!(\"field '{field_name}' is not mapped at this use site\"); }}"
    )
}

// Gets the full list ordered of generic parameters for a node. Outer scopes come first.
fn get_params(ctx: &GeneratorContext, mut node_id: u64) -> ::capnp::Result<Vec<String>> {
    let mut result = Vec::new();

    while node_id != 0 {
        let node = ctx.node_map[&node_id];
        let parameters = node.get_parameters()?;

        for parameter in parameters.into_iter().rev() {
            result.push(parameter.get_name()?.to_str()?.into());
        }

        node_id = node.get_scope_id();
    }

    result.reverse();
    Ok(result)
}

//
// Returns (type, getter body, default_decl)
//
pub fn getter_text(
    ctx: &GeneratorContext,
    field: &schema_capnp::field::Reader,
    is_reader: bool,
    is_fn: bool,
) -> ::capnp::Result<(String, FormattedText, Option<FormattedText>)> {
    getter_text_at(ctx, field, is_reader, is_fn, None)
}

// Like `getter_text`, but `offset_override`, when set, is used verbatim as the slot's offset
// expression instead of the field's baked literal. The erased `AnyReader`/`AnyBuilder` pass
// `self.offsets[i] as usize` so one type can serve every use site off a runtime offset table.
fn getter_text_at(
    ctx: &GeneratorContext,
    field: &schema_capnp::field::Reader,
    is_reader: bool,
    is_fn: bool,
    offset_override: Option<&str>,
) -> ::capnp::Result<(String, FormattedText, Option<FormattedText>)> {
    use capnp::schema_capnp::*;

    match field.which()? {
        field::Group(group) => {
            let params = get_params(ctx, group.get_type_id())?;
            let params_string = if params.is_empty() {
                "".to_string()
            } else {
                format!(",{}", params.join(","))
            };

            let the_mod = ctx.get_qualified_module(group.get_type_id());

            let mut result_type = if is_reader {
                format!("{the_mod}::Reader<'a{params_string}>")
            } else {
                format!("{the_mod}::Builder<'a{params_string}>")
            };

            if is_fn {
                result_type = format!("-> {result_type}");
            }

            let getter_code = if is_reader {
                line("self.reader.into()")
            } else {
                line("self.builder.into()")
            };

            Ok((result_type, getter_code, None))
        }
        field::Slot(reg_field) => {
            let mut default_decl = None;
            let offset: String = match offset_override {
                Some(e) => e.to_string(),
                None => (reg_field.get_offset() as usize).to_string(),
            };
            let module_string = if is_reader { "Reader" } else { "Builder" };
            let module = if is_reader {
                Leaf::Reader("'a")
            } else {
                Leaf::Builder("'a")
            };
            let member = camel_to_snake_case(module_string);

            fn primitive_case<T: PartialEq + ::std::fmt::Display>(
                typ: &str,
                member: &str,
                offset: &str,
                default: T,
                zero: T,
            ) -> String {
                if default == zero {
                    format!("self.{member}.get_data_field::<{typ}>({offset})")
                } else {
                    format!("self.{member}.get_data_field_mask::<{typ}>({offset}, {default})")
                }
            }

            let raw_type = reg_field.get_type()?;
            let inner_type = raw_type.type_string(ctx, module)?;
            let default_value = reg_field.get_default_value()?;
            let default = default_value.which()?;
            let default_name = format!(
                "DEFAULT_{}",
                camel_to_snake_case(get_field_name(*field)?).to_ascii_uppercase()
            );
            let should_get_option = is_option_field(*field)?;

            let typ = if should_get_option {
                format!("Option<{inner_type}>")
            } else {
                inner_type
            };

            let (is_fallible, mut result_type) = match raw_type.which()? {
                type_::Enum(_) => (
                    true,
                    fmt!(ctx, "::core::result::Result<{typ},{capnp}::NotInSchema>"),
                ),
                type_::AnyPointer(_) if !raw_type.is_parameter()? => (false, typ.clone()),
                type_::Interface(_) => (
                    true,
                    fmt!(
                        ctx,
                        "{capnp}::Result<{}>",
                        raw_type.type_string(ctx, Leaf::Client)?
                    ),
                ),
                _ if raw_type.is_prim()? => (false, typ.clone()),
                _ => (true, fmt!(ctx, "{capnp}::Result<{typ}>")),
            };

            if is_fn {
                result_type = if result_type == "()" {
                    "".to_string()
                } else {
                    format!("-> {result_type}")
                }
            }

            let getter_fragment = match (raw_type.which()?, default) {
                (type_::Void(()), value::Void(())) => {
                    if is_fn {
                        "".to_string()
                    } else {
                        "()".to_string()
                    }
                }
                (type_::Bool(()), value::Bool(b)) => {
                    if b {
                        format!("self.{member}.get_bool_field_mask({offset}, true)")
                    } else {
                        format!("self.{member}.get_bool_field({offset})")
                    }
                }
                (type_::Int8(()), value::Int8(i)) => primitive_case(&typ, &member, &offset, i, 0),
                (type_::Int16(()), value::Int16(i)) => primitive_case(&typ, &member, &offset, i, 0),
                (type_::Int32(()), value::Int32(i)) => primitive_case(&typ, &member, &offset, i, 0),
                (type_::Int64(()), value::Int64(i)) => primitive_case(&typ, &member, &offset, i, 0),
                (type_::Uint8(()), value::Uint8(i)) => primitive_case(&typ, &member, &offset, i, 0),
                (type_::Uint16(()), value::Uint16(i)) => {
                    primitive_case(&typ, &member, &offset, i, 0)
                }
                (type_::Uint32(()), value::Uint32(i)) => {
                    primitive_case(&typ, &member, &offset, i, 0)
                }
                (type_::Uint64(()), value::Uint64(i)) => {
                    primitive_case(&typ, &member, &offset, i, 0)
                }
                (type_::Float32(()), value::Float32(f)) => {
                    primitive_case(&typ, &member, &offset, f.to_bits(), 0)
                }
                (type_::Float64(()), value::Float64(f)) => {
                    primitive_case(&typ, &member, &offset, f.to_bits(), 0)
                }
                (type_::Enum(_), value::Enum(d)) => {
                    if d == 0 {
                        format!("::core::convert::TryFrom::try_from(self.{member}.get_data_field::<u16>({offset}))")
                    } else {
                        format!(
                                "::core::convert::TryFrom::try_from(self.{member}.get_data_field_mask::<u16>({offset}, {d}))")
                    }
                }

                (type_::Text(()), value::Text(_))
                | (type_::Data(()), value::Data(_))
                | (type_::List(_), value::List(_))
                | (type_::Struct(_), value::Struct(_)) => {
                    let default = if reg_field.get_had_explicit_default() {
                        default_decl = Some(crate::pointer_constants::word_array_declaration(
                            ctx,
                            &default_name,
                            ::capnp::raw::get_struct_pointer_section(default_value).get(0),
                            crate::pointer_constants::WordArrayDeclarationOptions {
                                pub_crate: true,
                            },
                        )?);
                        format!("::core::option::Option::Some(&_private::{default_name}[..])")
                    } else {
                        "::core::option::Option::None".to_string()
                    };

                    if is_reader {
                        fmt!(ctx,
                            "{capnp}::traits::FromPointerReader::get_from_pointer(&self.{member}.get_pointer_field({offset}), {default})")
                    } else {
                        fmt!(ctx,"{capnp}::traits::FromPointerBuilder::get_from_pointer(self.{member}.get_pointer_field({offset}), {default})")
                    }
                }

                (type_::Interface(_), value::Interface(_)) => {
                    fmt!(ctx,"match self.{member}.get_pointer_field({offset}).get_capability() {{ ::core::result::Result::Ok(c) => ::core::result::Result::Ok({capnp}::capability::FromClientHook::new(c)), ::core::result::Result::Err(e) => ::core::result::Result::Err(e)}}")
                }
                (type_::AnyPointer(_), value::AnyPointer(_)) => {
                    if !raw_type.is_parameter()? {
                        fmt!(ctx,"{capnp}::any_pointer::{module_string}::new(self.{member}.get_pointer_field({offset}))")
                    } else if is_reader {
                        fmt!(ctx,"{capnp}::traits::FromPointerReader::get_from_pointer(&self.{member}.get_pointer_field({offset}), ::core::option::Option::None)")
                    } else {
                        fmt!(ctx,"{capnp}::traits::FromPointerBuilder::get_from_pointer(self.{member}.get_pointer_field({offset}), ::core::option::Option::None)")
                    }
                }
                _ => return Err(Error::failed("default value was of wrong type".to_string())),
            };

            let getter_code = if should_get_option {
                Branch(vec![
                    Line(format!(
                        "if self.{member}.is_pointer_field_null({offset}) {{"
                    )),
                    indent(Line(
                        if is_fallible {
                            "core::result::Result::Ok(core::option::Option::None)"
                        } else {
                            "::core::option::Option::None"
                        }
                        .to_string(),
                    )),
                    Line("} else {".to_string()),
                    indent(Line(if is_fallible {
                        format!("{getter_fragment}.map(::core::option::Option::Some)")
                    } else {
                        format!("::core::option::Option::Some({getter_fragment})")
                    })),
                    Line("}".to_string()),
                ])
            } else {
                Line(getter_fragment)
            };

            Ok((result_type, getter_code, default_decl))
        }
    }
}

fn zero_fields_of_group(
    ctx: &GeneratorContext,
    node_id: u64,
    clear: &mut bool,
) -> ::capnp::Result<FormattedText> {
    use capnp::schema_capnp::{field, node, type_};
    match ctx.node_map[&node_id].which()? {
        node::Struct(st) => {
            let mut result = Vec::new();
            if st.get_discriminant_count() != 0 {
                result.push(Line(format!(
                    "self.builder.set_data_field::<u16>({}, 0);",
                    st.get_discriminant_offset()
                )));
            }
            let fields = st.get_fields()?;
            for field in fields {
                match field.which()? {
                    field::Group(group) => {
                        result.push(zero_fields_of_group(ctx, group.get_type_id(), clear)?);
                    }
                    field::Slot(slot) => {
                        let typ = slot.get_type()?.which()?;
                        match typ {
                            type_::Void(()) => {}
                            type_::Bool(()) => {
                                let line = Line(format!(
                                    "self.builder.set_bool_field({}, false);",
                                    slot.get_offset()
                                ));
                                // PERF could dedup more efficiently
                                if !result.contains(&line) {
                                    result.push(line)
                                }
                            }
                            type_::Int8(())
                            | type_::Int16(())
                            | type_::Int32(())
                            | type_::Int64(())
                            | type_::Uint8(())
                            | type_::Uint16(())
                            | type_::Uint32(())
                            | type_::Uint64(())
                            | type_::Float32(())
                            | type_::Float64(()) => {
                                let line = Line(format!(
                                    "self.builder.set_data_field::<{0}>({1}, 0{0});",
                                    slot.get_type()?.type_string(ctx, Leaf::Builder("'a"))?,
                                    slot.get_offset()
                                ));
                                // PERF could dedup more efficiently
                                if !result.contains(&line) {
                                    result.push(line)
                                }
                            }
                            type_::Enum(_) => {
                                let line = Line(format!(
                                    "self.builder.set_data_field::<u16>({}, 0u16);",
                                    slot.get_offset()
                                ));
                                // PERF could dedup more efficiently
                                if !result.contains(&line) {
                                    result.push(line)
                                }
                            }
                            type_::Struct(_)
                            | type_::List(_)
                            | type_::Text(())
                            | type_::Data(())
                            | type_::AnyPointer(_)
                            | type_::Interface(_) => {
                                // Is this the right thing to do for interfaces?
                                let line = Line(format!(
                                    "self.builder.reborrow().get_pointer_field({}).clear();",
                                    slot.get_offset()
                                ));
                                *clear = true;
                                // PERF could dedup more efficiently
                                if !result.contains(&line) {
                                    result.push(line)
                                }
                            }
                        }
                    }
                }
            }
            Ok(Branch(result))
        }
        _ => Err(Error::failed(
            "zero_fields_of_group() expected a struct".to_string(),
        )),
    }
}

// One builder mutator (a `set_`, `init_`, or `initn_` method), split into its signature pieces
// and body so both the inherent `impl` and a newtype's Builder trait can be generated from a
// single source. `receiver`/`params`/`ret` compose the signature; `delegate_args` names the
// arguments a trait impl forwards when delegating to the inherent method.
struct SetterMethod {
    name: String,
    receiver: String,
    params: String,
    ret: String,
    body: FormattedText,
    delegate_args: String,
}

impl SetterMethod {
    // The signature as it appears after `fn`, e.g. `set_foo(&mut self, value: i32)`. `bind_mut`
    // keeps a `mut self` receiver (the inherent body needs it); a delegating trait impl passes
    // false since it never mutates `self` locally.
    fn signature(&self, bind_mut: bool) -> String {
        let receiver = if bind_mut {
            self.receiver.clone()
        } else {
            self.receiver.trim_start_matches("mut ").to_string()
        };
        let args = if self.params.is_empty() {
            receiver
        } else {
            format!("{receiver}, {}", self.params)
        };
        let ret = if self.ret.is_empty() {
            String::new()
        } else {
            format!(" {}", self.ret)
        };
        format!("{}({args}){ret}", self.name)
    }
}

fn setter_methods(
    ctx: &GeneratorContext,
    discriminant_offset: u32,
    styled_name: &str,
    field: &schema_capnp::field::Reader,
) -> ::capnp::Result<Vec<SetterMethod>> {
    setter_methods_at(
        ctx,
        &(discriminant_offset as usize).to_string(),
        styled_name,
        field,
        None,
    )
}

// Like `setter_methods`, but with the discriminant offset and (via `offset_override`) the slot
// offset given as expressions, so the erased `AnyBuilder` can write at `self.offsets[i]` /
// `self.disc_offset` instead of baked literals.
fn setter_methods_at(
    ctx: &GeneratorContext,
    disc_offset: &str,
    styled_name: &str,
    field: &schema_capnp::field::Reader,
    offset_override: Option<&str>,
) -> ::capnp::Result<Vec<SetterMethod>> {
    use capnp::schema_capnp::*;

    let mut setter_interior = Vec::new();
    let mut setter_param = "value".to_string();
    let mut initter_interior = Vec::new();
    let mut initter_mut = false;
    let mut initn_interior = Vec::new();
    let mut initter_params = Vec::new();

    let discriminant_value = field.get_discriminant_value();
    if discriminant_value != field::NO_DISCRIMINANT {
        setter_interior.push(Line(format!(
            "self.builder.set_data_field::<u16>({}, {});",
            disc_offset, discriminant_value as usize
        )));
        let init_discrim = Line(format!(
            "self.builder.set_data_field::<u16>({}, {});",
            disc_offset, discriminant_value as usize
        ));
        initter_interior.push(init_discrim.clone());
        initn_interior.push(init_discrim);
    }

    let mut return_result = false;
    let mut methods: Vec<SetterMethod> = Vec::new();

    let (maybe_reader_type, maybe_builder_type): (Option<String>, Option<String>) = match field
        .which()?
    {
        field::Group(group) => {
            let params = get_params(ctx, group.get_type_id())?;
            let params_string = if params.is_empty() {
                "".to_string()
            } else {
                format!(",{}", params.join(","))
            };

            let the_mod = ctx.get_qualified_module(group.get_type_id());

            initter_interior.push(zero_fields_of_group(
                ctx,
                group.get_type_id(),
                &mut initter_mut,
            )?);

            initter_interior.push(line("self.builder.into()"));

            (None, Some(format!("{the_mod}::Builder<'a{params_string}>")))
        }
        field::Slot(reg_field) => {
            let offset: String = match offset_override {
                Some(e) => e.to_string(),
                None => (reg_field.get_offset() as usize).to_string(),
            };
            let typ = reg_field.get_type()?;
            match typ.which().expect("unrecognized type") {
                type_::Void(()) => {
                    setter_param = "_value".to_string();
                    (Some("()".to_string()), None)
                }
                type_::Bool(()) => {
                    match prim_default(&reg_field.get_default_value()?)? {
                        None => {
                            setter_interior.push(Line(format!(
                                "self.builder.set_bool_field({offset}, value);"
                            )));
                        }
                        Some(s) => {
                            setter_interior.push(Line(format!(
                                "self.builder.set_bool_field_mask({offset}, value, {s});"
                            )));
                        }
                    }
                    (Some("bool".to_string()), None)
                }
                _ if typ.is_prim()? => {
                    let tstr = typ.type_string(ctx, Leaf::Reader("'a"))?;
                    match prim_default(&reg_field.get_default_value()?)? {
                        None => {
                            setter_interior.push(Line(format!(
                                "self.builder.set_data_field::<{tstr}>({offset}, value);"
                            )));
                        }
                        Some(s) => {
                            setter_interior.push(Line(format!(
                                "self.builder.set_data_field_mask::<{tstr}>({offset}, value, {s});"
                            )));
                        }
                    };
                    (Some(tstr), None)
                }
                type_::Text(()) => {
                    // The text::Reader impl of SetterInput never fails, so we can unwrap().
                    setter_interior.push(Line(fmt!(ctx,
                        "{capnp}::traits::SetterInput::set_pointer_builder(self.builder.reborrow().get_pointer_field({offset}), value, false).unwrap()"
                    )));
                    initter_interior.push(Line(format!(
                        "self.builder.get_pointer_field({offset}).init_text(size)"
                    )));
                    initter_params.push("size: u32");
                    (
                        Some(fmt!(
                            ctx,
                            "impl {capnp}::traits::SetterInput<{capnp}::text::Owned>"
                        )),
                        Some(fmt!(ctx, "{capnp}::text::Builder<'a>")),
                    )
                }
                type_::Data(()) => {
                    setter_interior.push(Line(format!(
                        "self.builder.reborrow().get_pointer_field({offset}).set_data(value);"
                    )));
                    initter_interior.push(Line(format!(
                        "self.builder.get_pointer_field({offset}).init_data(size)"
                    )));
                    initter_params.push("size: u32");
                    (
                        Some(fmt!(ctx, "{capnp}::data::Reader<'_>")),
                        Some(fmt!(ctx, "{capnp}::data::Builder<'a>")),
                    )
                }
                type_::List(ls) => {
                    let et = ls.get_element_type()?;
                    return_result = true;
                    setter_interior.push(
                        Line(fmt!(ctx,"{capnp}::traits::SetterInput::set_pointer_builder(self.builder.reborrow().get_pointer_field({offset}), value, false)")));

                    initter_params.push("size: u32");
                    initter_interior.push(
                        Line(fmt!(ctx,"{capnp}::traits::FromPointerBuilder::init_pointer(self.builder.get_pointer_field({offset}), size)")));

                    let mr = match et.which()? {
                        type_::Void(())
                        | type_::Bool(())
                        | type_::Int8(())
                        | type_::Int16(())
                        | type_::Int32(())
                        | type_::Int64(())
                        | type_::Uint8(())
                        | type_::Uint16(())
                        | type_::Uint32(())
                        | type_::Uint64(())
                        | type_::Float32(())
                        | type_::Float64(())
                        | type_::Enum(_)
                        | type_::Text(()) => {
                            // There are multiple SetterInput impls.
                            fmt!(
                                ctx,
                                "impl {capnp}::traits::SetterInput<{}>",
                                reg_field.get_type()?.type_string(ctx, Leaf::Owned)?
                            )
                        }
                        _ => reg_field.get_type()?.type_string(ctx, Leaf::Reader("'_"))?,
                    };

                    (
                        Some(mr),
                        Some(
                            reg_field
                                .get_type()?
                                .type_string(ctx, Leaf::Builder("'a"))?,
                        ),
                    )
                }
                type_::Enum(e) => {
                    let id = e.get_type_id();
                    let the_mod = ctx.get_qualified_module(id);
                    if !reg_field.get_had_explicit_default() {
                        setter_interior.push(Line(format!(
                            "self.builder.set_data_field::<u16>({offset}, value as u16);"
                        )));
                    } else {
                        match reg_field.get_default_value()?.which()? {
                            schema_capnp::value::Enum(d) => {
                                setter_interior.push(Line(format!(
                                    "self.builder.set_data_field_mask::<u16>({offset}, value as u16, {d});"
                                )));
                            }
                            _ => return Err(Error::failed("enum default not an Enum".to_string())),
                        }
                    };
                    (Some(the_mod), None)
                }
                type_::Struct(_) => {
                    return_result = true;
                    initter_interior.push(
                      Line(fmt!(ctx,"{capnp}::traits::FromPointerBuilder::init_pointer(self.builder.get_pointer_field({offset}), 0)")));
                    setter_interior.push(
                        Line(fmt!(ctx,"{capnp}::traits::SetterInput::set_pointer_builder(self.builder.reborrow().get_pointer_field({offset}), value, false)")));

                    (
                        Some(typ.type_string(ctx, Leaf::Reader("'_"))?),
                        Some(typ.type_string(ctx, Leaf::Builder("'a"))?),
                    )
                }
                type_::Interface(_) => {
                    setter_interior.push(Line(format!(
                        "self.builder.reborrow().get_pointer_field({offset}).set_capability(value.client.hook);"
                    )));
                    (Some(typ.type_string(ctx, Leaf::Client)?), None)
                }
                type_::AnyPointer(_) => {
                    if typ.is_parameter()? {
                        initter_interior.push(Line(fmt!(ctx,"{capnp}::any_pointer::Builder::new(self.builder.get_pointer_field({offset})).init_as()")));
                        setter_interior.push(Line(fmt!(ctx,"{capnp}::traits::SetterInput::set_pointer_builder(self.builder.reborrow().get_pointer_field({offset}), value, false)")));
                        return_result = true;

                        let builder_type = typ.type_string(ctx, Leaf::Builder("'a"))?;

                        methods.push(SetterMethod {
                            name: format!("initn_{styled_name}"),
                            receiver: "self".into(),
                            params: "length: u32".into(),
                            ret: format!("-> {builder_type}"),
                            body: Branch(vec![
                                Branch(initn_interior),
                                Line(fmt!(ctx,"{capnp}::any_pointer::Builder::new(self.builder.get_pointer_field({offset})).initn_as(length)")),
                            ]),
                            delegate_args: "length".into(),
                        });

                        (
                            Some(fmt!(
                                ctx,
                                "impl {capnp}::traits::SetterInput<{}>",
                                typ.type_string(ctx, Leaf::Owned)?
                            )),
                            Some(builder_type),
                        )
                    } else {
                        initter_interior.push(Line(fmt!(ctx,"let mut result = {capnp}::any_pointer::Builder::new(self.builder.get_pointer_field({offset}));")));
                        initter_interior.push(line("result.clear();"));
                        initter_interior.push(line("result"));
                        (None, Some(fmt!(ctx, "{capnp}::any_pointer::Builder<'a>")))
                    }
                }
                _ => return Err(Error::failed("unrecognized type".to_string())),
            }
        }
    };
    if let Some(reader_type) = maybe_reader_type {
        let ret = if return_result {
            fmt!(ctx, "-> {capnp}::Result<()>")
        } else {
            String::new()
        };
        methods.push(SetterMethod {
            name: format!("set_{styled_name}"),
            receiver: "&mut self".into(),
            params: format!("{setter_param}: {reader_type}"),
            ret,
            body: Branch(setter_interior),
            delegate_args: setter_param.clone(),
        });
    }
    if let Some(builder_type) = maybe_builder_type {
        let arg_names: Vec<&str> = initter_params
            .iter()
            .map(|p| p.split(':').next().unwrap_or("").trim())
            .collect();
        methods.push(SetterMethod {
            name: format!("init_{styled_name}"),
            receiver: if initter_mut { "mut self" } else { "self" }.into(),
            params: initter_params.join(", "),
            ret: format!("-> {builder_type}"),
            body: Branch(initter_interior),
            delegate_args: arg_names.join(", "),
        });
    }
    Ok(methods)
}

// Assembles the inherent builder mutators for a field from `setter_methods`.
fn generate_setter(
    ctx: &GeneratorContext,
    discriminant_offset: u32,
    styled_name: &str,
    field: &schema_capnp::field::Reader,
) -> ::capnp::Result<FormattedText> {
    let mut result = Vec::new();
    for m in setter_methods(ctx, discriminant_offset, styled_name, field)? {
        result.push(line("#[inline]"));
        result.push(Line(format!("pub fn {} {{", m.signature(true))));
        result.push(indent(m.body));
        result.push(line("}"));
    }
    Ok(Branch(result))
}

fn used_params_of_group(
    ctx: &GeneratorContext,
    group_id: u64,
    used_params: &mut HashSet<String>,
) -> capnp::Result<()> {
    let node = ctx.node_map[&group_id];
    match node.which()? {
        schema_capnp::node::Struct(st) => {
            for field in st.get_fields()? {
                match field.which()? {
                    schema_capnp::field::Group(group) => {
                        used_params_of_group(ctx, group.get_type_id(), used_params)?;
                    }
                    schema_capnp::field::Slot(slot) => {
                        used_params_of_type(ctx, slot.get_type()?, used_params)?;
                    }
                }
            }
            Ok(())
        }
        _ => Err(Error::failed("not a group".to_string())),
    }
}

fn used_params_of_type(
    ctx: &GeneratorContext,
    ty: schema_capnp::type_::Reader,
    used_params: &mut HashSet<String>,
) -> capnp::Result<()> {
    use capnp::schema_capnp::type_;
    match ty.which()? {
        type_::List(ls) => {
            let et = ls.get_element_type()?;
            used_params_of_type(ctx, et, used_params)?;
        }
        type_::Enum(e) => {
            let node_id = e.get_type_id();
            let brand = e.get_brand()?;
            used_params_of_brand(ctx, node_id, brand, used_params)?;
        }
        type_::Struct(s) => {
            let node_id = s.get_type_id();
            let brand = s.get_brand()?;
            used_params_of_brand(ctx, node_id, brand, used_params)?;
        }
        type_::Interface(i) => {
            let node_id = i.get_type_id();
            let brand = i.get_brand()?;
            used_params_of_brand(ctx, node_id, brand, used_params)?;
        }

        type_::AnyPointer(ap) => {
            if let type_::any_pointer::Parameter(def) = ap.which()? {
                let the_struct = &ctx.node_map[&def.get_scope_id()];
                let parameters = the_struct.get_parameters()?;
                let parameter = parameters.get(u32::from(def.get_parameter_index()));
                let parameter_name = parameter.get_name()?.to_str()?;
                used_params.insert(parameter_name.to_string());
            }
        }
        _ => (),
    }
    Ok(())
}

fn used_params_of_brand(
    ctx: &GeneratorContext,
    node_id: u64,
    brand: schema_capnp::brand::Reader,
    used_params: &mut HashSet<String>,
) -> capnp::Result<()> {
    use schema_capnp::brand;
    let scopes = brand.get_scopes()?;
    let mut brand_scopes = HashMap::new();
    for scope in scopes {
        brand_scopes.insert(scope.get_scope_id(), scope);
    }
    let brand_scopes = brand_scopes; // freeze
    let mut current_node_id = node_id;
    while let Some(current_node) = ctx.node_map.get(&current_node_id) {
        let params = current_node.get_parameters()?;
        match brand_scopes.get(&current_node_id) {
            None => (),
            Some(scope) => match scope.which()? {
                brand::scope::Inherit(()) => {
                    for param in params {
                        used_params.insert(param.get_name()?.to_string()?);
                    }
                }
                brand::scope::Bind(bindings_list_opt) => {
                    let bindings_list = bindings_list_opt?;
                    assert_eq!(bindings_list.len(), params.len());
                    for binding in bindings_list {
                        match binding.which()? {
                            brand::binding::Unbound(()) => (),
                            brand::binding::Type(t) => {
                                used_params_of_type(ctx, t?, used_params)?;
                            }
                        }
                    }
                }
            },
        }
        current_node_id = current_node.get_scope_id();
    }
    Ok(())
}

// return (the 'Which' enum, the 'which()' accessor, typedef, default_decls)
fn generate_union(
    ctx: &GeneratorContext,
    discriminant_offset: u32,
    fields: &[schema_capnp::field::Reader],
    is_reader: bool,
    params: &TypeParameterTexts,
) -> ::capnp::Result<(
    FormattedText,
    FormattedText,
    FormattedText,
    Vec<FormattedText>,
)> {
    use capnp::schema_capnp::*;

    fn new_ty_param(ty_params: &mut Vec<String>) -> String {
        let result = format!("A{}", ty_params.len());
        ty_params.push(result.clone());
        result
    }

    let mut getter_interior = Vec::new();
    let mut interior = Vec::new();
    let mut enum_interior = Vec::new();
    let mut default_decls = Vec::new();

    let mut ty_params = Vec::new();
    let mut ty_args = Vec::new();

    let mut used_params: HashSet<String> = HashSet::new();

    let doffset = discriminant_offset as usize;

    for field in fields {
        let dvalue = field.get_discriminant_value() as usize;

        let field_name = get_field_name(*field)?;
        let enumerant_name = capitalize_first_letter(field_name);

        let (ty, get, maybe_default_decl) = getter_text(ctx, field, is_reader, false)?;
        if let Some(default_decl) = maybe_default_decl {
            default_decls.push(default_decl)
        }

        getter_interior.push(Branch(vec![
            Line(format!("{dvalue} => {{")),
            indent(Line(format!(
                "::core::result::Result::Ok({}(",
                enumerant_name.clone()
            ))),
            indent(indent(get)),
            indent(line("))")),
            line("}"),
        ]));

        let ty1 = match field.which() {
            Ok(field::Group(group)) => {
                used_params_of_group(ctx, group.get_type_id(), &mut used_params)?;
                ty_args.push(ty);
                new_ty_param(&mut ty_params)
            }
            Ok(field::Slot(reg_field)) => {
                let fty = reg_field.get_type()?;
                used_params_of_type(ctx, fty, &mut used_params)?;
                match fty.which() {
                    Ok(
                        type_::Text(())
                        | type_::Data(())
                        | type_::List(_)
                        | type_::Struct(_)
                        | type_::AnyPointer(_),
                    ) => {
                        ty_args.push(ty);
                        new_ty_param(&mut ty_params)
                    }
                    Ok(type_::Interface(_)) => ty,
                    _ => ty,
                }
            }
            _ => ty,
        };

        enum_interior.push(Line(format!("{enumerant_name}({ty1}),")));
    }

    let enum_name = format!(
        "Which{}",
        if !ty_params.is_empty() {
            format!("<{}>", ty_params.join(","))
        } else {
            "".to_string()
        }
    );

    getter_interior.push(Line(fmt!(
        ctx,
        "x => ::core::result::Result::Err({capnp}::NotInSchema(x))"
    )));

    interior.push(Branch(vec![
        Line(format!("pub enum {enum_name} {{")),
        indent(enum_interior),
        line("}"),
    ]));

    let result = Branch(interior);

    let field_name = if is_reader { "reader" } else { "builder" };

    let concrete_type = format!(
        "Which{}{}",
        if is_reader { "Reader" } else { "Builder" },
        if !ty_params.is_empty() {
            format!(
                "<'a,{}>",
                params
                    .expanded_list
                    .iter()
                    .filter(|s: &&String| used_params.contains(*s))
                    .cloned()
                    .collect::<Vec<String>>()
                    .join(",")
            )
        } else {
            "".to_string()
        }
    );

    let typedef = Line(format!(
        "pub type {concrete_type} = Which{};",
        if !ty_args.is_empty() {
            format!("<{}>", ty_args.join(","))
        } else {
            "".to_string()
        }
    ));

    let getter_result = Branch(vec![
        line("#[inline]"),
        Line(fmt!(ctx,
            "pub fn which(self) -> ::core::result::Result<{concrete_type}, {capnp}::NotInSchema> {{"
        )),
        indent(vec![
            Line(format!(
                "match self.{field_name}.get_data_field::<u16>({doffset}) {{"
            )),
            indent(getter_interior),
            line("}"),
        ]),
        line("}"),
    ]);

    // TODO set_which() for builders?

    Ok((result, getter_result, typedef, default_decls))
}

fn generate_haser(
    discriminant_offset: u32,
    styled_name: &str,
    field: &schema_capnp::field::Reader,
    is_reader: bool,
) -> ::capnp::Result<FormattedText> {
    use capnp::schema_capnp::*;

    let mut result = Vec::new();
    let mut interior = Vec::new();
    let member = if is_reader { "reader" } else { "builder" };

    let discriminant_value = field.get_discriminant_value();
    if discriminant_value != field::NO_DISCRIMINANT {
        interior.push(Line(format!(
            "if self.{}.get_data_field::<u16>({}) != {} {{ return false; }}",
            member, discriminant_offset as usize, discriminant_value as usize
        )));
    }
    match field.which() {
        Err(_) | Ok(field::Group(_)) => {}
        Ok(field::Slot(reg_field)) => match reg_field.get_type()?.which()? {
            type_::Text(())
            | type_::Data(())
            | type_::List(_)
            | type_::Struct(_)
            | type_::Interface(_)
            | type_::AnyPointer(_) => {
                if is_reader {
                    interior.push(Line(format!(
                        "!self.{member}.get_pointer_field({}).is_null()",
                        reg_field.get_offset()
                    )));
                } else {
                    interior.push(Line(format!(
                        "!self.{member}.is_pointer_field_null({})",
                        reg_field.get_offset()
                    )));
                }
                result.push(line("#[inline]"));
                result.push(Line(format!("pub fn has_{styled_name}(&self) -> bool {{")));
                result.push(indent(interior));
                result.push(line("}"));
            }
            _ => {}
        },
    }

    Ok(Branch(result))
}

fn generate_pipeline_getter(
    ctx: &GeneratorContext,
    field: schema_capnp::field::Reader,
) -> ::capnp::Result<FormattedText> {
    use capnp::schema_capnp::{field, type_};

    let name = get_field_name(field)?;

    match field.which()? {
        field::Group(group) => {
            let params = get_params(ctx, group.get_type_id())?;
            let params_string = if params.is_empty() {
                "".to_string()
            } else {
                format!("<{}>", params.join(","))
            };

            let the_mod = ctx.get_qualified_module(group.get_type_id());
            Ok(Branch(vec![
                Line(format!(
                    "pub fn get_{}(&self) -> {}::Pipeline{} {{",
                    camel_to_snake_case(name),
                    the_mod,
                    params_string
                )),
                indent(Line(fmt!(
                    ctx,
                    "{capnp}::capability::FromTypelessPipeline::new(self._typeless.noop())"
                ))),
                line("}"),
            ]))
        }
        field::Slot(reg_field) => {
            let typ = reg_field.get_type()?;
            match typ.which()? {
                type_::Struct(_) | type_::AnyPointer(_) => {
                    Ok(Branch(vec![
                        Line(format!("pub fn get_{}(&self) -> {} {{", camel_to_snake_case(name), typ.type_string(ctx, Leaf::Pipeline)?)),
                        indent(Line(fmt!(ctx,"{capnp}::capability::FromTypelessPipeline::new(self._typeless.get_pointer_field({}))", reg_field.get_offset()))),
                        line("}")
                    ]))
                }
                type_::Interface(_) => {
                    Ok(Branch(vec![
                        Line(format!("pub fn get_{}(&self) -> {} {{", camel_to_snake_case(name), typ.type_string(ctx, Leaf::Client)?)),
                        indent(Line(fmt!(ctx,"{capnp}::capability::FromClientHook::new(self._typeless.get_pointer_field({}).as_cap())", reg_field.get_offset()))),
                        line("}")
                    ]))
                }
                _ => {
                    Ok(Branch(Vec::new()))
                }
            }
        }
    }
}

fn generate_get_field_types(
    ctx: &GeneratorContext,
    node_reader: schema_capnp::node::Reader,
) -> ::capnp::Result<FormattedText> {
    use capnp::schema_capnp::field;
    let st = match node_reader.which()? {
        schema_capnp::node::Struct(st) => st,
        _ => return Err(Error::failed("not a struct".into())),
    };
    let mut branches = vec![];
    for (index, field) in st.get_fields()?.iter().enumerate() {
        match field.which()? {
            field::Slot(slot) => {
                let raw_type = slot.get_type()?;
                let typ = raw_type.type_string(ctx, Leaf::Owned)?;
                branches.push(Line(fmt!(
                    ctx,
                    "{} => <{} as {capnp}::introspect::Introspect>::introspect(),",
                    index,
                    typ
                )));
            }
            field::Group(group) => {
                let params = get_params(ctx, group.get_type_id())?;
                let params_string = if params.is_empty() {
                    "".to_string()
                } else {
                    format!("<{}>", params.join(","))
                };

                let the_mod = ctx.get_qualified_module(group.get_type_id());

                let typ = format!("{the_mod}::Owned{params_string}");
                branches.push(Line(fmt!(
                    ctx,
                    "{} => <{} as {capnp}::introspect::Introspect>::introspect(),",
                    index,
                    typ
                )));
            }
        }
    }
    let body = if branches.is_empty() {
        Line(fmt!(
            ctx,
            "{capnp}::introspect::panic_invalid_field_index(index)"
        ))
    } else {
        branches.push(Line(fmt!(
            ctx,
            "_ => {capnp}::introspect::panic_invalid_field_index(index),"
        )));
        Branch(vec![
            Line("match index {".into()),
            indent(branches),
            Line("}".into()),
        ])
    };
    if !node_reader.get_is_generic() {
        Ok(Branch(vec![
            Line(fmt!(
                ctx,
                "pub(crate) fn get_field_types(index: u16) -> {capnp}::introspect::Type {{"
            )),
            indent(body),
            Line("}".into()),
        ]))
    } else {
        let params = node_reader.parameters_texts(ctx);
        Ok(Branch(vec![
            Line(fmt!(
                ctx,
                "pub(crate) fn get_field_types<{0}>(index: u16) -> {capnp}::introspect::Type {1} {{",
                params.params,
                params.where_clause
            )),
            indent(body),
            Line("}".into()),
        ]))
    }
}

fn annotation_branch(
    ctx: &GeneratorContext,
    annotation: schema_capnp::annotation::Reader,
    child_index: Option<u16>,
    index: u32,
) -> ::capnp::Result<FormattedText> {
    use capnp::schema_capnp::node;
    let id = annotation.get_id();
    let annotation_decl = ctx.node_map[&id];
    let node::Annotation(a) = annotation_decl.which()? else {
        return Err(Error::failed("not an annotation node".into()));
    };
    if annotation_decl.get_is_generic() {
        let brand = annotation.get_brand()?;
        let the_mod = ctx.get_qualified_module(id);
        let func = do_branding(ctx, id, brand, Leaf::GetType, &the_mod)?;
        Ok(Line(format!("({child_index:?}, {index}) => {func}(),")))
    } else {
        // Avoid referring to the annotation in the generated code, so that users can import
        // annotation schemas like `c++.capnp` or `rust.capnp` without needing to generate code
        // for them, as long as the annotations are not generic.
        let ty = a.get_type()?;
        Ok(Line(fmt!(
            ctx,
            "({child_index:?}, {index}) => <{} as {capnp}::introspect::Introspect>::introspect(),",
            ty.type_string(ctx, Leaf::Owned)?
        )))
    }
}

fn generate_get_annotation_types(
    ctx: &GeneratorContext,
    node_reader: schema_capnp::node::Reader,
) -> ::capnp::Result<FormattedText> {
    use capnp::schema_capnp::node;

    let mut branches = vec![];

    for (idx, annotation) in node_reader.get_annotations()?.iter().enumerate() {
        branches.push(annotation_branch(ctx, annotation, None, idx as u32)?);
    }

    match node_reader.which()? {
        node::Struct(s) => {
            for (fidx, field) in s.get_fields()?.iter().enumerate() {
                for (idx, annotation) in field.get_annotations()?.iter().enumerate() {
                    branches.push(annotation_branch(
                        ctx,
                        annotation,
                        Some(fidx as u16),
                        idx as u32,
                    )?);
                }
            }
        }
        node::Enum(e) => {
            for (fidx, enumerant) in e.get_enumerants()?.iter().enumerate() {
                for (idx, annotation) in enumerant.get_annotations()?.iter().enumerate() {
                    branches.push(annotation_branch(
                        ctx,
                        annotation,
                        Some(fidx as u16),
                        idx as u32,
                    )?);
                }
            }
        }
        _ => (),
    }

    let body = if branches.is_empty() {
        Line(fmt!(
            ctx,
            "{capnp}::introspect::panic_invalid_annotation_indices(child_index, index)"
        ))
    } else {
        branches.push(Line(fmt!(
            ctx,
            "_ => {capnp}::introspect::panic_invalid_annotation_indices(child_index, index),"
        )));
        indent(vec![
            Line("match (child_index, index) {".into()),
            indent(branches),
            Line("}".into()),
        ])
    };

    if !node_reader.get_is_generic() {
        Ok(Branch(vec![
            Line(fmt!(ctx,"pub(crate) fn get_annotation_types(child_index: Option<u16>, index: u32) -> {capnp}::introspect::Type {{")),
            indent(body),
            Line("}".into()),
        ]))
    } else {
        let params = node_reader.parameters_texts(ctx);
        Ok(Branch(vec![
            Line(fmt!(ctx,
                "pub(crate) fn get_annotation_types<{0}>(child_index: Option<u16>, index: u32) -> {capnp}::introspect::Type {1} {{",
                params.params, params.where_clause
            )),
            indent(body),
            Line("}".into()),
        ]))
    }
}

fn generate_members_by_discriminant(
    node_reader: schema_capnp::node::Reader,
) -> ::capnp::Result<FormattedText> {
    use capnp::schema_capnp::field;
    let st = match node_reader.which()? {
        schema_capnp::node::Struct(st) => st,
        _ => return Err(Error::failed("not a struct".into())),
    };

    let mut union_member_indexes = vec![];
    let mut nonunion_member_indexes = vec![];
    for (index, field) in st.get_fields()?.iter().enumerate() {
        let disc = field.get_discriminant_value();
        if disc == field::NO_DISCRIMINANT {
            nonunion_member_indexes.push(index);
        } else {
            union_member_indexes.push((disc, index));
        }
    }
    union_member_indexes.sort();

    let mut nonunion_string: String = "pub(crate) static NONUNION_MEMBERS : &[u16] = &[".into();
    for idx in 0..nonunion_member_indexes.len() {
        nonunion_string += &format!("{}", nonunion_member_indexes[idx]);
        if idx + 1 < nonunion_member_indexes.len() {
            nonunion_string += ",";
        }
    }
    nonunion_string += "];";

    let mut members_by_disc: String =
        "pub(crate) static MEMBERS_BY_DISCRIMINANT : &[u16] = &[".into();
    for idx in 0..union_member_indexes.len() {
        let (disc, index) = union_member_indexes[idx];
        assert_eq!(idx, disc as usize);
        members_by_disc += &format!("{index}");
        if idx + 1 < union_member_indexes.len() {
            members_by_disc += ",";
        }
    }
    members_by_disc += "];";
    Ok(Branch(vec![Line(nonunion_string), Line(members_by_disc)]))
}

fn generate_members_by_name(
    node_reader: schema_capnp::node::Reader,
) -> ::capnp::Result<FormattedText> {
    let st = match node_reader.which()? {
        schema_capnp::node::Struct(st) => st,
        _ => return Err(Error::failed("not a struct".into())),
    };

    let mut members_by_name = Vec::new();
    for (index, field) in st.get_fields()?.iter().enumerate() {
        if let Ok(name) = get_field_name(field) {
            members_by_name.push((name, index));
        }
    }
    members_by_name.sort_by_key(|k| k.0);

    let mut members_by_name_string: String =
        "pub(crate) static MEMBERS_BY_NAME : &[u16] = &[".into();
    for (i, (_, index)) in members_by_name.iter().enumerate() {
        members_by_name_string += &format!("{}", *index);
        if i + 1 < members_by_name.len() {
            members_by_name_string += ",";
        }
    }
    members_by_name_string += "];";

    Ok(Branch(vec![Line(members_by_name_string)]))
}

// The `type` newtypes a field was declared with, nearest first. A field declared `corner
// :ChainedPoint`, where `type ChainedPoint = Point` and `type Point = Vec3`, gives [ChainedPoint,
// Point, Vec3]. Empty for a field not declared with a newtype. A group field records its newtype
// in `Field.typeId`; a slot field in its type's `Type.typeId`. Each `type` node records the
// newtype it aliases (if any) in its own `Type.typeId`, which is how the chain is followed. A
// newtype whose node isn't in the request ends the chain there.
fn field_newtype_ids(
    ctx: &GeneratorContext,
    field: schema_capnp::field::Reader,
) -> ::capnp::Result<Vec<u64>> {
    use capnp::schema_capnp::*;
    let mut id = field.get_type_id();
    if id == 0 {
        if let field::Slot(slot) = field.which()? {
            id = slot.get_type()?.get_type_id();
        }
    }
    let mut ids = Vec::new();
    // The schema compiler rejects alias cycles; the `contains` check only stops a malformed
    // request from looping forever.
    while id != 0 && !ids.contains(&id) {
        ids.push(id);
        let Some(node) = ctx.node_map.get(&id) else {
            break;
        };
        let node::Type(Ok(t)) = node.which()? else {
            break;
        };
        id = t.get_type_id();
    }
    Ok(ids)
}

// `FIELD_NEWTYPES`: for each field index, the newtype ids from `field_newtype_ids`. None (and
// nothing is emitted) when no field of the struct is declared with a newtype, which keeps
// generated code for schemas without newtypes unchanged.
fn generate_field_newtypes(
    ctx: &GeneratorContext,
    node_reader: schema_capnp::node::Reader,
) -> ::capnp::Result<Option<FormattedText>> {
    let schema_capnp::node::Struct(st) = node_reader.which()? else {
        return Err(Error::failed("not a struct".into()));
    };
    let mut any = false;
    let mut entries = Vec::new();
    for field in st.get_fields()? {
        let ids = field_newtype_ids(ctx, field)?;
        any |= !ids.is_empty();
        let ids: Vec<String> = ids.into_iter().map(format_u64).collect();
        entries.push(format!("&[{}]", ids.join(", ")));
    }
    if !any {
        return Ok(None);
    }
    Ok(Some(Line(format!(
        "pub(crate) static FIELD_NEWTYPES: &[&[u64]] = &[{}];",
        entries.join(", ")
    ))))
}

// We need this to work around the fact that Rust does not allow typedefs
// with unused type parameters.
fn get_ty_params_of_brand(
    ctx: &GeneratorContext,
    brand: schema_capnp::brand::Reader,
) -> ::capnp::Result<String> {
    let mut acc = HashSet::new();
    get_ty_params_of_brand_helper(ctx, &mut acc, brand)?;
    let mut result = String::new();
    for (scope_id, parameter_index) in acc.into_iter() {
        let node = ctx.node_map[&scope_id];
        let p = node.get_parameters()?.get(u32::from(parameter_index));
        result.push_str(p.get_name()?.to_str()?);
        result.push(',');
    }

    Ok(result)
}

fn get_ty_params_of_type_helper(
    ctx: &GeneratorContext,
    accumulator: &mut HashSet<(u64, u16)>,
    typ: schema_capnp::type_::Reader,
) -> ::capnp::Result<()> {
    use capnp::schema_capnp::type_;
    match typ.which()? {
        type_::Void(())
        | type_::Bool(())
        | type_::Int8(())
        | type_::Int16(())
        | type_::Int32(())
        | type_::Int64(())
        | type_::Uint8(())
        | type_::Uint16(())
        | type_::Uint32(())
        | type_::Uint64(())
        | type_::Float32(())
        | type_::Float64(())
        | type_::Text(_)
        | type_::Data(_) => {}
        type_::AnyPointer(p) => {
            match p.which()? {
                type_::any_pointer::Unconstrained(_) => (),
                type_::any_pointer::Parameter(p) => {
                    accumulator.insert((p.get_scope_id(), p.get_parameter_index()));
                }
                type_::any_pointer::ImplicitMethodParameter(_) => {
                    // XXX
                }
            }
        }
        type_::List(list) => {
            get_ty_params_of_type_helper(ctx, accumulator, list.get_element_type()?)?
        }
        type_::Enum(e) => {
            get_ty_params_of_brand_helper(ctx, accumulator, e.get_brand()?)?;
        }
        type_::Struct(s) => {
            get_ty_params_of_brand_helper(ctx, accumulator, s.get_brand()?)?;
        }
        type_::Interface(interf) => {
            get_ty_params_of_brand_helper(ctx, accumulator, interf.get_brand()?)?;
        }
    }
    Ok(())
}

fn get_ty_params_of_brand_helper(
    ctx: &GeneratorContext,
    accumulator: &mut HashSet<(u64, u16)>,
    brand: schema_capnp::brand::Reader,
) -> ::capnp::Result<()> {
    for scope in brand.get_scopes()? {
        let scope_id = scope.get_scope_id();
        match scope.which()? {
            schema_capnp::brand::scope::Bind(bind) => {
                for binding in bind? {
                    match binding.which()? {
                        schema_capnp::brand::binding::Unbound(()) => {}
                        schema_capnp::brand::binding::Type(t) => {
                            get_ty_params_of_type_helper(ctx, accumulator, t?)?
                        }
                    }
                }
            }
            schema_capnp::brand::scope::Inherit(()) => {
                let parameters = ctx.node_map[&scope_id].get_parameters()?;
                for idx in 0..parameters.len() {
                    accumulator.insert((scope_id, idx as u16));
                }
            }
        }
    }
    Ok(())
}

// A `type` newtype declaration (`type Vec3 = group { ... }`) is represented as a `type` node
// whose target is a struct pointing at a template node the newtype owns (its `scope_id` is the
// `type` node). We give such a newtype a semantic trait -- `vec3::Reader` -- so every use site
// shares one name. Returns the template node's id when `alias_id` is an inline group/union
// newtype, or a `type` aliasing one (`type Bar = Foo`), which shares Foo's template.
fn newtype_template_id(ctx: &GeneratorContext, alias_id: u64) -> ::capnp::Result<Option<u64>> {
    use capnp::schema_capnp::*;
    let Some(alias) = ctx.node_map.get(&alias_id) else {
        return Ok(None);
    };
    let node::Type(Ok(t)) = alias.which()? else {
        return Ok(None);
    };
    let type_::Struct(st) = t.which()? else {
        return Ok(None); // scalar newtype -- rendered via its underlying type
    };
    let template_id = st.get_type_id();
    let Some(template) = ctx.node_map.get(&template_id) else {
        return Ok(None);
    };
    if template.get_scope_id() != alias_id {
        // Not this node's own template. Either it aliases another inline newtype (recorded as
        // Type.typeId), whose template it shares, or it names a pre-existing struct.
        let aliased = t.get_type_id();
        if aliased != 0 {
            return newtype_template_id(ctx, aliased);
        }
        return Ok(None);
    }
    Ok(Some(template_id))
}

// The inline newtype owning `alias_id`'s template: `alias_id` itself, or for `type Bar = Foo`
// (Foo an inline group/union newtype), Foo. None if `alias_id` isn't an inline newtype.
fn inline_newtype_owner(ctx: &GeneratorContext, alias_id: u64) -> ::capnp::Result<Option<u64>> {
    Ok(newtype_template_id(ctx, alias_id)?.map(|t| ctx.node_map[&t].get_scope_id()))
}

// A non-union group newtype. Its fields are slots and/or nested-newtype members (group fields
// carrying a `Field.typeId`, surfaced as associated types). A plain anonymous group field is not
// yet supported.
fn group_newtype_template_id(
    ctx: &GeneratorContext,
    alias_id: u64,
) -> ::capnp::Result<Option<u64>> {
    use capnp::schema_capnp::*;
    let Some(template_id) = newtype_template_id(ctx, alias_id)? else {
        return Ok(None);
    };
    let node::Struct(tmpl) = ctx.node_map[&template_id].which()? else {
        return Ok(None);
    };
    if tmpl.get_discriminant_count() > 0 {
        return Ok(None); // union newtype -- handled separately
    }
    for field in tmpl.get_fields()? {
        if let field::Group(_) = field.which()? {
            if field.get_type_id() == 0 {
                return Ok(None); // anonymous group member -- not a newtype, deferred
            }
        }
    }
    Ok(Some(template_id))
}

// A union newtype. Slot arms have use-site-independent `Which` payloads; a group arm is a nested
// newtype, surfaced through an associated type. An anonymous group arm is not yet supported.
fn union_newtype_template_id(
    ctx: &GeneratorContext,
    alias_id: u64,
) -> ::capnp::Result<Option<u64>> {
    use capnp::schema_capnp::*;
    let Some(template_id) = newtype_template_id(ctx, alias_id)? else {
        return Ok(None);
    };
    let node::Struct(tmpl) = ctx.node_map[&template_id].which()? else {
        return Ok(None);
    };
    if tmpl.get_discriminant_count() == 0 {
        return Ok(None); // not a union
    }
    for field in tmpl.get_fields()? {
        if let field::Group(_) = field.which()? {
            if field.get_type_id() == 0 {
                return Ok(None); // anonymous group arm -- not a newtype, deferred
            }
        }
    }
    Ok(Some(template_id))
}

// One method of a newtype's Reader/Builder trait: its signature (the text after `fn`) plus how a
// delegating impl forwards to the inherent accessor. Reader getters take `&self`, but the inherent
// reader accessor consumes `self` (readers are `Copy`), so they forward through `(*self)`.
struct TraitMethod {
    signature: String,
    call_name: String,
    call_args: String,
    deref_self: bool,
}

// The Reader- or Builder-side trait methods mirroring one template field's inherent accessors:
// a getter (both sides), the mutators (Builder side), and `has_` for a pointer field (both sides).
fn newtype_trait_methods(
    ctx: &GeneratorContext,
    field: &schema_capnp::field::Reader,
    is_reader: bool,
    include_getter: bool,
) -> ::capnp::Result<Vec<TraitMethod>> {
    use capnp::schema_capnp::*;
    let name = camel_to_snake_case(field.get_name()?.to_str()?);
    let is_pointer = match field.which()? {
        field::Slot(s) => s.get_type()?.is_pointer()?,
        field::Group(_) => false,
    };
    let mut methods = Vec::new();

    // Union arms have no inherent getter -- they are read through `which()` -- so unions pass
    // include_getter = false; a delegating getter would just recurse.
    if is_reader {
        if include_getter {
            let (ret, _, _) = getter_text(ctx, field, true, true)?;
            methods.push(TraitMethod {
                signature: format!("get_{name}(&self) {ret}"),
                call_name: format!("get_{name}"),
                call_args: String::new(),
                deref_self: true,
            });
        }
    } else {
        if include_getter {
            // Builder getters consume `self` (they hand out the child builder), matching the
            // inherent accessor, so no deref.
            let (ret, _, _) = getter_text(ctx, field, false, true)?;
            methods.push(TraitMethod {
                signature: format!("get_{name}(self) {ret}"),
                call_name: format!("get_{name}"),
                call_args: String::new(),
                deref_self: false,
            });
        }
        for m in setter_methods(ctx, 0, &name, field)? {
            methods.push(TraitMethod {
                signature: m.signature(false),
                call_name: m.name,
                call_args: m.delegate_args,
                deref_self: false,
            });
        }
    }
    if is_pointer {
        methods.push(TraitMethod {
            signature: format!("has_{name}(&self) -> bool"),
            call_name: format!("has_{name}"),
            call_args: String::new(),
            deref_self: false,
        });
    }
    Ok(methods)
}

// The id of a `type` newtype's node, as `pub const TYPE_ID` in its module. An alias module
// (`type Bar = Foo`) declares its own, which takes precedence over the one its `pub use` of
// Foo's module brings in, so each name reports its own id. It is what
// `schema::Field::get_newtype_ids` returns, so code can recognise a newtype at runtime.
fn newtype_type_id_line(node_id: u64) -> FormattedText {
    Line(format!("pub const TYPE_ID: u64 = {};", format_u64(node_id)))
}

// Emits the trait module for a newtype: a flat group (`generate_flat_newtype_trait`) or a union
// (`generate_union_newtype_trait`). Exactly one applies (or neither); each no-ops otherwise.
fn generate_newtype_trait(
    ctx: &GeneratorContext,
    node_id: u64,
    node_name: &str,
) -> ::capnp::Result<FormattedText> {
    if let Some(owner) = inline_newtype_owner(ctx, node_id)? {
        if owner != node_id {
            // `type Bar = Foo` with Foo an inline newtype: Bar's module re-exports Foo's, so
            // `bar::Reader` *is* `foo::Reader` and Bar's use sites implement Foo's traits.
            return Ok(Branch(vec![
                BlankLine,
                Line(format!("pub mod {} {{", module_name(node_name))),
                indent(Line(format!(
                    "pub use {}::*;",
                    ctx.get_qualified_module(owner)
                ))),
                indent(newtype_type_id_line(node_id)),
                line("}"),
            ]));
        }
    }
    Ok(Branch(vec![
        generate_group_newtype_trait(ctx, node_id, node_name)?,
        generate_union_newtype_trait(ctx, node_id, node_name)?,
    ]))
}

// Recursive leaf count of a newtype template: a slot is one leaf; a nested-newtype member expands
// to its own leaves. The erased carrier uses this to slice its offset table.
fn count_newtype_leaves(ctx: &GeneratorContext, template_id: u64) -> ::capnp::Result<usize> {
    use capnp::schema_capnp::*;
    let node::Struct(tmpl) = ctx.node_map[&template_id].which()? else {
        return Ok(0);
    };
    let mut n = 0;
    for field in tmpl.get_fields()? {
        match field.which()? {
            field::Slot(_) => n += 1,
            field::Group(_) => {
                if let Some(nested) = newtype_template_id(ctx, field.get_type_id())? {
                    n += count_newtype_leaves(ctx, nested)?;
                }
            }
        }
    }
    Ok(n)
}

// Collects a use site's leaf offsets in template (tree) order, recursing through nested-newtype
// members, matching the instance's fields to the template by name. A leaf absent from the instance
// (an incomplete `@[...]`) gets the sentinel `0xffff_ffff`.
fn collect_leaf_offsets(
    ctx: &GeneratorContext,
    template_id: u64,
    instance_id: u64,
    out: &mut Vec<String>,
) -> ::capnp::Result<()> {
    use capnp::schema_capnp::*;
    let node::Struct(tmpl) = ctx.node_map[&template_id].which()? else {
        return Ok(());
    };
    let node::Struct(instance) = ctx.node_map[&instance_id].which()? else {
        return Ok(());
    };
    let mut inst_fields = ::std::collections::HashMap::new();
    for f in instance.get_fields()? {
        inst_fields.insert(f.get_name()?.to_str()?.to_string(), f);
    }
    for field in tmpl.get_fields()? {
        let raw = field.get_name()?.to_str()?;
        match field.which()? {
            field::Slot(_) => match inst_fields.get(raw).map(|f| f.which()) {
                Some(Ok(field::Slot(s))) => out.push(s.get_offset().to_string()),
                _ => out.push("0xffff_ffff".to_string()),
            },
            field::Group(_) => {
                let Some(nested_tmpl) = newtype_template_id(ctx, field.get_type_id())? else {
                    continue;
                };
                match inst_fields.get(raw).map(|f| f.which()) {
                    Some(Ok(field::Group(ig))) => {
                        collect_leaf_offsets(ctx, nested_tmpl, ig.get_type_id(), out)?
                    }
                    _ => {
                        for _ in 0..count_newtype_leaves(ctx, nested_tmpl)? {
                            out.push("0xffff_ffff".to_string());
                        }
                    }
                }
            }
        }
    }
    Ok(())
}

// The erased carrier for a (non-union) group newtype: a concrete `AnyReader<'a>` holding a
// `StructReader` plus a runtime offset table, so one type serves every use site (unlike `&dyn`).
// A slot accessor indexes `self.offsets[i]` via `getter_text_at`; a nested-newtype member returns
// the member's own `AnyReader` over a sub-slice of the table. It impls the newtype's `Reader`
// trait, so `impl Reader` bounds accept both the concrete per-site type and the erased form.
fn any_reader_items(
    ctx: &GeneratorContext,
    template_id: u64,
) -> ::capnp::Result<Vec<FormattedText>> {
    use capnp::schema_capnp::*;
    let node::Struct(tmpl) = ctx.node_map[&template_id].which()? else {
        return Ok(vec![]);
    };
    if tmpl.get_discriminant_count() > 0 {
        return Ok(vec![]); // union newtype -- separate carrier
    }

    let mut inherent = Vec::new();
    let mut trait_methods = Vec::new();
    let mut defaults = Vec::new();
    let mut cursor = 0usize;
    for field in tmpl.get_fields()? {
        let name = camel_to_snake_case(field.get_name()?.to_str()?);
        if let field::Group(_) = field.which()? {
            let assoc = capitalize_first_letter(field.get_name()?.to_str()?);
            let nested_mod = ctx.get_qualified_module(field.get_type_id());
            let Some(nested_tmpl) = newtype_template_id(ctx, field.get_type_id())? else {
                return Ok(vec![]);
            };
            let count = count_newtype_leaves(ctx, nested_tmpl)?;
            let (start, end) = (cursor, cursor + count);
            inherent.push(Line(format!(
                "pub fn get_{name}(&self) -> {nested_mod}::AnyReader<'a> {{ {nested_mod}::AnyReader::new(self.reader, &self.offsets[{start}..{end}]) }}"
            )));
            trait_methods.push(Line(format!("type {assoc} = {nested_mod}::AnyReader<'a>;")));
            trait_methods.push(Line(format!(
                "fn get_{name}(&self) -> Self::{assoc} {{ self.get_{name}() }}"
            )));
            cursor += count;
        } else {
            let off = format!("self.offsets[{cursor}] as usize");
            let (ret, mut body, def) = getter_text_at(ctx, &field, true, true, Some(&off))?;
            if let Some(d) = def {
                defaults.push(d);
            }
            // An unmapped leaf (sentinel offset) reads its default rather than dereferencing the
            // sentinel -- matching C++, and 32-bit-safe (the out-of-range read would overflow).
            if is_scalar_data_field(&field)? {
                if let (field::Slot(s), FormattedText::Line(expr)) = (field.which()?, &body) {
                    let expr = expr.clone();
                    let dflt = prim_default_value(&s.get_default_value()?)?;
                    body = Line(format!(
                        "if self.offsets[{cursor}] == 0xffff_ffffu32 {{ {dflt} }} else {{ {expr} }}"
                    ));
                }
            }
            inherent.push(Line(format!("pub fn get_{name}(&self) {ret} {{")));
            inherent.push(indent(body));
            inherent.push(line("}"));
            trait_methods.push(Line(format!(
                "fn get_{name}(&self) {ret} {{ self.get_{name}() }}"
            )));
            if let field::Slot(s) = field.which()? {
                if s.get_type()?.is_pointer()? {
                    inherent.push(Line(format!(
                        "pub fn has_{name}(&self) -> bool {{ !self.reader.get_pointer_field(self.offsets[{cursor}] as usize).is_null() }}"
                    )));
                    trait_methods.push(Line(format!(
                        "fn has_{name}(&self) -> bool {{ self.has_{name}() }}"
                    )));
                }
            }
            cursor += 1;
        }
    }

    let sr = fmt!(ctx, "{capnp}::private::layout::StructReader<'a>");
    let mut items = vec![
        BlankLine,
        line("#[derive(Clone, Copy)]"),
        Line(format!(
            "pub struct AnyReader<'a> {{ reader: {sr}, offsets: &'a [u32] }}"
        )),
        line("impl<'a> AnyReader<'a> {"),
        indent(vec![
            Line(format!(
                "pub fn new(reader: {sr}, offsets: &'a [u32]) -> Self {{ AnyReader {{ reader, offsets }} }}"
            )),
            Branch(inherent),
        ]),
        line("}"),
        line("impl<'a> Reader<'a> for AnyReader<'a> {"),
        indent(trait_methods),
        line("}"),
    ];
    if !defaults.is_empty() {
        items.push(line("mod _private {"));
        items.push(indent(defaults));
        items.push(line("}"));
    }
    Ok(items)
}

// The erased carrier for a union newtype: like `AnyReader` but with a runtime discriminant offset.
// `which()` reads the discriminant and builds the shared `Which`, with a group arm yielding the
// member's own `AnyReader` over an offset sub-slice -- so the erased union unifies across use sites
// (which `&dyn` cannot, given the arm associated types).
fn union_any_reader_items(
    ctx: &GeneratorContext,
    template_id: u64,
) -> ::capnp::Result<Vec<FormattedText>> {
    use capnp::schema_capnp::*;
    let node::Struct(tmpl) = ctx.node_map[&template_id].which()? else {
        return Ok(vec![]);
    };
    if tmpl.get_discriminant_count() == 0 {
        return Ok(vec![]);
    }

    let mut arms = Vec::new();
    let mut assoc = Vec::new();
    let mut group_variants = Vec::new();
    let mut which_type_params = Vec::new();
    let mut has_inherent = Vec::new();
    let mut has_trait = Vec::new();
    let mut needs_lifetime = false;
    let mut cursor = 0usize;
    for field in tmpl.get_fields()? {
        let variant = capitalize_first_letter(field.get_name()?.to_str()?);
        let name = camel_to_snake_case(field.get_name()?.to_str()?);
        let dvalue = field.get_discriminant_value();
        if let field::Group(_) = field.which()? {
            let nested_mod = ctx.get_qualified_module(field.get_type_id());
            let Some(nested_tmpl) = newtype_template_id(ctx, field.get_type_id())? else {
                return Ok(vec![]);
            };
            let count = count_newtype_leaves(ctx, nested_tmpl)?;
            let (start, end) = (cursor, cursor + count);
            arms.push(Line(format!(
                "{dvalue} => ::core::result::Result::Ok(Which::{variant}({nested_mod}::AnyReader::new(self.reader, &self.offsets[{start}..{end}]))),"
            )));
            assoc.push(Line(format!(
                "type {variant} = {nested_mod}::AnyReader<'a>;"
            )));
            group_variants.push(variant.clone());
            which_type_params.push(format!("{nested_mod}::AnyReader<'a>"));
            cursor += count;
        } else {
            let off = format!("self.offsets[{cursor}] as usize");
            let (_, getter_code, _) = getter_text_at(ctx, &field, true, false, Some(&off))?;
            let FormattedText::Line(payload) = getter_code else {
                return Ok(vec![]); // option-wrapped arm -- unsupported in the erased union for now
            };
            arms.push(Line(format!(
                "{dvalue} => ::core::result::Result::Ok(Which::{variant}({payload})),"
            )));
            if let field::Slot(s) = field.which()? {
                if s.get_type()?.is_pointer()? {
                    needs_lifetime = true;
                    has_inherent.push(Line(format!(
                        "pub fn has_{name}(&self) -> bool {{ if self.reader.get_data_field::<u16>(self.disc_offset as usize) != {dvalue} {{ return false; }} !self.reader.get_pointer_field(self.offsets[{cursor}] as usize).is_null() }}"
                    )));
                    has_trait.push(Line(format!(
                        "fn has_{name}(&self) -> bool {{ self.has_{name}() }}"
                    )));
                }
            }
            cursor += 1;
        }
    }
    arms.push(line(
        "x => ::core::result::Result::Err(::capnp::NotInSchema(x)),",
    ));

    let inherent_ret = union_which_generics(needs_lifetime, &which_type_params);
    let self_ret = union_which_generics(
        needs_lifetime,
        &group_variants
            .iter()
            .map(|v| format!("Self::{v}"))
            .collect::<Vec<_>>(),
    );

    let sr = fmt!(ctx, "{capnp}::private::layout::StructReader<'a>");
    let which_method = Branch(vec![
        Line(format!(
            "pub fn which(&self) -> ::core::result::Result<Which{inherent_ret}, ::capnp::NotInSchema> {{"
        )),
        indent(vec![
            line("match self.reader.get_data_field::<u16>(self.disc_offset as usize) {"),
            indent(arms),
            line("}"),
        ]),
        line("}"),
    ]);

    let mut trait_items = assoc;
    trait_items.push(Line(format!(
        "fn which(&self) -> ::core::result::Result<Which{self_ret}, ::capnp::NotInSchema> {{ self.which() }}"
    )));
    trait_items.extend(has_trait);

    Ok(vec![
        BlankLine,
        line("#[derive(Clone, Copy)]"),
        Line(format!(
            "pub struct AnyReader<'a> {{ reader: {sr}, disc_offset: u32, offsets: &'a [u32] }}"
        )),
        line("impl<'a> AnyReader<'a> {"),
        indent(vec![
            Line(format!(
                "pub fn new(reader: {sr}, disc_offset: u32, offsets: &'a [u32]) -> Self {{ AnyReader {{ reader, disc_offset, offsets }} }}"
            )),
            which_method,
            Branch(has_inherent),
        ]),
        line("}"),
        line("impl<'a> Reader<'a> for AnyReader<'a> {"),
        indent(trait_items),
        line("}"),
    ])
}

// The erased mutable carrier for a (non-union) group newtype: `AnyBuilder<'a>` over a
// `StructBuilder` and a runtime offset table. Setters/init write at `self.offsets[i]`; a
// nested-newtype member yields the member's own `AnyBuilder` over a sub-slice.
fn any_builder_items(
    ctx: &GeneratorContext,
    template_id: u64,
) -> ::capnp::Result<Vec<FormattedText>> {
    use capnp::schema_capnp::*;
    let node::Struct(tmpl) = ctx.node_map[&template_id].which()? else {
        return Ok(vec![]);
    };
    if tmpl.get_discriminant_count() > 0 {
        return Ok(vec![]); // union AnyBuilder -- deferred
    }

    let mut inherent = Vec::new();
    let mut trait_methods = Vec::new();
    let mut cursor = 0usize;
    for field in tmpl.get_fields()? {
        let name = camel_to_snake_case(field.get_name()?.to_str()?);
        if let field::Group(_) = field.which()? {
            let assoc = capitalize_first_letter(field.get_name()?.to_str()?);
            let nested_mod = ctx.get_qualified_module(field.get_type_id());
            let Some(nested_tmpl) = newtype_template_id(ctx, field.get_type_id())? else {
                return Ok(vec![]);
            };
            let count = count_newtype_leaves(ctx, nested_tmpl)?;
            let (start, end) = (cursor, cursor + count);
            for verb in ["get", "init"] {
                inherent.push(Line(format!(
                    "pub fn {verb}_{name}(self) -> {nested_mod}::AnyBuilder<'a> {{ {nested_mod}::AnyBuilder::new(self.builder, &self.offsets[{start}..{end}]) }}"
                )));
            }
            trait_methods.push(Line(format!(
                "type {assoc} = {nested_mod}::AnyBuilder<'a>;"
            )));
            trait_methods.push(Line(format!(
                "fn get_{name}(self) -> Self::{assoc} {{ self.get_{name}() }}"
            )));
            trait_methods.push(Line(format!(
                "fn init_{name}(self) -> Self::{assoc} {{ self.init_{name}() }}"
            )));
            cursor += count;
        } else {
            let off = format!("self.offsets[{cursor}] as usize");
            let guard = unmapped_panic(cursor, &name);
            // Builder getter: a scalar reads its default at the sentinel; a pointer getter panics
            // (the builder read is unchecked and there's no empty builder to return).
            let (ret, body, _) = getter_text_at(ctx, &field, false, true, Some(&off))?;
            let get_body = if is_scalar_data_field(&field)? {
                if let field::Slot(s) = field.which()? {
                    if let FormattedText::Line(expr) = &body {
                        let expr = expr.clone();
                        let dflt = prim_default_value(&s.get_default_value()?)?;
                        Line(format!(
                            "if self.offsets[{cursor}] == 0xffff_ffffu32 {{ {dflt} }} else {{ {expr} }}"
                        ))
                    } else {
                        body
                    }
                } else {
                    body
                }
            } else {
                Branch(vec![Line(guard.clone()), body])
            };
            inherent.push(Line(format!("pub fn get_{name}(self) {ret} {{")));
            inherent.push(indent(get_body));
            inherent.push(line("}"));
            trait_methods.push(Line(format!(
                "fn get_{name}(self) {ret} {{ self.get_{name}() }}"
            )));
            for m in setter_methods_at(ctx, "0", &name, &field, Some(&off))? {
                let sig_inherent = m.signature(true);
                let sig_trait = m.signature(false);
                let call = format!("self.{}({})", m.name, m.delegate_args);
                inherent.push(Line(format!("pub fn {sig_inherent} {{")));
                inherent.push(indent(Branch(vec![Line(guard.clone()), m.body])));
                inherent.push(line("}"));
                trait_methods.push(Line(format!("fn {sig_trait} {{ {call} }}")));
            }
            if let field::Slot(s) = field.which()? {
                if s.get_type()?.is_pointer()? {
                    inherent.push(Line(format!(
                        "pub fn has_{name}(&self) -> bool {{ if self.offsets[{cursor}] == 0xffff_ffffu32 {{ return false; }} !self.builder.is_pointer_field_null(self.offsets[{cursor}] as usize) }}"
                    )));
                    trait_methods.push(Line(format!(
                        "fn has_{name}(&self) -> bool {{ self.has_{name}() }}"
                    )));
                }
            }
            cursor += 1;
        }
    }

    let sb = fmt!(ctx, "{capnp}::private::layout::StructBuilder<'a>");
    Ok(vec![
        BlankLine,
        Line(format!(
            "pub struct AnyBuilder<'a> {{ builder: {sb}, offsets: &'a [u32] }}"
        )),
        line("impl<'a> AnyBuilder<'a> {"),
        indent(vec![
            Line(format!(
                "pub fn new(builder: {sb}, offsets: &'a [u32]) -> Self {{ AnyBuilder {{ builder, offsets }} }}"
            )),
            Branch(inherent),
        ]),
        line("}"),
        line("impl<'a> Builder<'a> for AnyBuilder<'a> {"),
        indent(trait_methods),
        line("}"),
    ])
}

// The erased mutable carrier for a union newtype: `AnyBuilder` with a runtime discriminant offset.
// Each arm setter writes the discriminant at `self.disc_offset` (via `setter_methods_at`); a group
// arm's `init_` writes it then hands out the member's own `AnyBuilder` over an offset sub-slice.
fn union_any_builder_items(
    ctx: &GeneratorContext,
    template_id: u64,
) -> ::capnp::Result<Vec<FormattedText>> {
    use capnp::schema_capnp::*;
    let node::Struct(tmpl) = ctx.node_map[&template_id].which()? else {
        return Ok(vec![]);
    };
    if tmpl.get_discriminant_count() == 0 {
        return Ok(vec![]);
    }

    let mut inherent = Vec::new();
    let mut assoc = Vec::new();
    let mut trait_methods = Vec::new();
    let mut cursor = 0usize;
    for field in tmpl.get_fields()? {
        let variant = capitalize_first_letter(field.get_name()?.to_str()?);
        let name = camel_to_snake_case(field.get_name()?.to_str()?);
        let dvalue = field.get_discriminant_value();
        if let field::Group(_) = field.which()? {
            let nested_mod = ctx.get_qualified_module(field.get_type_id());
            let Some(nested_tmpl) = newtype_template_id(ctx, field.get_type_id())? else {
                return Ok(vec![]);
            };
            let count = count_newtype_leaves(ctx, nested_tmpl)?;
            let (start, end) = (cursor, cursor + count);
            inherent.push(Line(format!(
                "pub fn init_{name}(self) -> {nested_mod}::AnyBuilder<'a> {{ let b = self.builder; b.set_data_field::<u16>(self.disc_offset as usize, {dvalue}); {nested_mod}::AnyBuilder::new(b, &self.offsets[{start}..{end}]) }}"
            )));
            assoc.push(Line(format!(
                "type {variant} = {nested_mod}::AnyBuilder<'a>;"
            )));
            trait_methods.push(Line(format!(
                "fn init_{name}(self) -> Self::{variant} {{ self.init_{name}() }}"
            )));
            cursor += count;
        } else {
            let off = format!("self.offsets[{cursor}] as usize");
            let guard = unmapped_panic(cursor, &name);
            for m in setter_methods_at(ctx, "self.disc_offset as usize", &name, &field, Some(&off))?
            {
                let sig_inherent = m.signature(true);
                let sig_trait = m.signature(false);
                let call = format!("self.{}({})", m.name, m.delegate_args);
                inherent.push(Line(format!("pub fn {sig_inherent} {{")));
                inherent.push(indent(Branch(vec![Line(guard.clone()), m.body])));
                inherent.push(line("}"));
                trait_methods.push(Line(format!("fn {sig_trait} {{ {call} }}")));
            }
            if let field::Slot(s) = field.which()? {
                if s.get_type()?.is_pointer()? {
                    inherent.push(Line(format!(
                        "pub fn has_{name}(&self) -> bool {{ if self.builder.get_data_field::<u16>(self.disc_offset as usize) != {dvalue} {{ return false; }} !self.builder.is_pointer_field_null(self.offsets[{cursor}] as usize) }}"
                    )));
                    trait_methods.push(Line(format!(
                        "fn has_{name}(&self) -> bool {{ self.has_{name}() }}"
                    )));
                }
            }
            cursor += 1;
        }
    }

    let sb = fmt!(ctx, "{capnp}::private::layout::StructBuilder<'a>");
    let mut trait_items = assoc;
    trait_items.extend(trait_methods);
    Ok(vec![
        BlankLine,
        Line(format!(
            "pub struct AnyBuilder<'a> {{ builder: {sb}, disc_offset: u32, offsets: &'a [u32] }}"
        )),
        line("impl<'a> AnyBuilder<'a> {"),
        indent(vec![
            Line(format!(
                "pub fn new(builder: {sb}, disc_offset: u32, offsets: &'a [u32]) -> Self {{ AnyBuilder {{ builder, disc_offset, offsets }} }}"
            )),
            Branch(inherent),
        ]),
        line("}"),
        line("impl<'a> Builder<'a> for AnyBuilder<'a> {"),
        indent(trait_items),
        line("}"),
    ])
}

// `capnp::traits::AnyReader` / `AnyBuilder` for a newtype's erased carriers, plus the
// `DowncastReader` / `DowncastBuilder` impls through which the dynamic API reaches them:
// `group.downcast::<vec3::AnyReader>()`. The downcast reads the use site's offset table from the
// group's schema (see `use_site_any_layout`) and checks it against `TYPE_ID` and `LEAF_COUNT`.
fn any_downcast_impls(
    ctx: &GeneratorContext,
    template_id: u64,
    is_union: bool,
    has_reader: bool,
    has_builder: bool,
) -> ::capnp::Result<Vec<FormattedText>> {
    let leaves = count_newtype_leaves(ctx, template_id)?;
    // A union carrier's `new` takes the discriminant offset; a group carrier's doesn't.
    let disc_arg = if is_union {
        "discriminant_offset, "
    } else {
        ""
    };
    let mut items = Vec::new();
    let mut emit = |kind: &str, raw: &str, value: &str, downcast: &str| {
        let ident = kind.to_ascii_lowercase();
        let unused = if is_union { "" } else { "_" };
        items.push(Line(fmt!(
            ctx,
            "impl<'a> {capnp}::traits::{kind}<'a> for {kind}<'a> {{"
        )));
        items.push(indent(vec![
            line("const TYPE_ID: u64 = TYPE_ID;"),
            Line(format!("const LEAF_COUNT: usize = {leaves};")),
            Line(fmt!(ctx,
                "fn from_use_site({ident}: {capnp}::private::layout::{raw}<'a>, offsets: &'a [u32], {unused}discriminant_offset: u32) -> Self {{ Self::new({ident}, {disc_arg}offsets) }}"
            )),
        ]));
        items.push(line("}"));
        items.push(Line(fmt!(
            ctx,
            "impl<'a> {capnp}::dynamic_value::Downcast{value}<'a> for {kind}<'a> {{"
        )));
        items.push(indent(Line(fmt!(ctx,
            "fn downcast_{value_lc}(v: {capnp}::dynamic_value::{value}<'a>) -> Self {{ {capnp}::dynamic_value::{downcast}(v) }}",
            value_lc = value.to_ascii_lowercase()
        ))));
        items.push(line("}"));
    };
    if has_reader {
        emit("AnyReader", "StructReader", "Reader", "downcast_any_reader");
    }
    if has_builder {
        emit(
            "AnyBuilder",
            "StructBuilder",
            "Builder",
            "downcast_any_builder",
        );
    }
    Ok(items)
}

// For a group that is a use site of a group or union newtype, the `.with_any_layout(..)` call that
// records the newtype ids and offset table on its `RAW_SCHEMA`, so the dynamic API can downcast it.
// The offset table is the one the parent's module already emits for `as_any()` (named by
// `use_site_offsets_table`); a private item of an ancestor module is visible here. None for any
// other node.
fn use_site_any_layout(
    ctx: &GeneratorContext,
    node: schema_capnp::node::Reader,
) -> ::capnp::Result<Option<String>> {
    use capnp::schema_capnp::*;
    let node::Struct(instance) = node.which()? else {
        return Ok(None);
    };
    if !instance.get_is_group() {
        return Ok(None);
    }
    let id = node.get_id();
    let Some(parent) = ctx.node_map.get(&node.get_scope_id()) else {
        return Ok(None);
    };
    let node::Struct(parent_struct) = parent.which()? else {
        return Ok(None);
    };
    for field in parent_struct.get_fields()? {
        let field::Group(group) = field.which()? else {
            continue;
        };
        if group.get_type_id() != id || field.get_type_id() == 0 {
            continue;
        }
        let alias_id = field.get_type_id();
        let is_newtype = group_newtype_template_id(ctx, alias_id)?.is_some()
            || union_newtype_template_id(ctx, alias_id)?.is_some();
        if !is_newtype {
            return Ok(None);
        }
        let ids: Vec<String> = field_newtype_ids(ctx, field)?
            .into_iter()
            .map(format_u64)
            .collect();
        let table = use_site_offsets_table(ctx, node.get_scope_id(), id)?;
        return Ok(Some(format!(
            ".with_any_layout(&[{}], &{table}, {})",
            ids.join(", "),
            instance.get_discriminant_offset()
        )));
    }
    Ok(None)
}

// The path of the `*_OFFSETS` static for the use-site group `instance_id`, emitted in the module of
// its parent struct `parent_id`.
fn use_site_offsets_table(
    ctx: &GeneratorContext,
    parent_id: u64,
    instance_id: u64,
) -> ::capnp::Result<String> {
    Ok(format!(
        "{}::{}",
        ctx.get_qualified_module(parent_id),
        use_site_offsets_name(ctx, instance_id)?
    ))
}

fn use_site_offsets_name(ctx: &GeneratorContext, instance_id: u64) -> ::capnp::Result<String> {
    Ok(format!(
        "{}_OFFSETS",
        camel_to_snake_case(ctx.get_last_name(instance_id)?).to_ascii_uppercase()
    ))
}

// Emits `pub mod <name> { pub trait Reader<'a> {...} pub trait Builder<'a> {...} }` for a non-union
// group newtype. Slot fields mirror the per-use-site accessors; a nested-newtype member (a group
// field) is surfaced as an associated type bounded by that newtype's trait, plus a getter.
fn generate_group_newtype_trait(
    ctx: &GeneratorContext,
    node_id: u64,
    node_name: &str,
) -> ::capnp::Result<FormattedText> {
    use capnp::schema_capnp::*;
    let Some(template_id) = group_newtype_template_id(ctx, node_id)? else {
        return Ok(Branch(vec![]));
    };
    let node::Struct(tmpl) = ctx.node_map[&template_id].which()? else {
        return Ok(Branch(vec![]));
    };

    let mut reader_items = Vec::new();
    let mut builder_items = Vec::new();
    for field in tmpl.get_fields()? {
        if let field::Group(_) = field.which()? {
            // Nested newtype member: an associated type bounded by the member's trait, plus a
            // getter (and builder init) -- no whole-value setter, same as a struct field.
            let name = camel_to_snake_case(field.get_name()?.to_str()?);
            let assoc = capitalize_first_letter(field.get_name()?.to_str()?);
            let nested = ctx.get_qualified_module(field.get_type_id());
            reader_items.push(Line(format!("type {assoc}: {nested}::Reader<'a>;")));
            reader_items.push(Line(format!("fn get_{name}(&self) -> Self::{assoc};")));
            builder_items.push(Line(format!("type {assoc}: {nested}::Builder<'a>;")));
            builder_items.push(Line(format!("fn get_{name}(self) -> Self::{assoc};")));
            builder_items.push(Line(format!("fn init_{name}(self) -> Self::{assoc};")));
        } else {
            for m in newtype_trait_methods(ctx, &field, true, true)? {
                reader_items.push(Line(format!("fn {};", m.signature)));
            }
            for m in newtype_trait_methods(ctx, &field, false, true)? {
                builder_items.push(Line(format!("fn {};", m.signature)));
            }
        }
    }

    let mut module_items = vec![
        line("pub trait Reader<'a> {"),
        indent(reader_items),
        line("}"),
        line("pub trait Builder<'a> {"),
        indent(builder_items),
        line("}"),
    ];
    let any_reader = any_reader_items(ctx, template_id)?;
    let any_builder = any_builder_items(ctx, template_id)?;
    let downcasts = any_downcast_impls(
        ctx,
        template_id,
        false,
        !any_reader.is_empty(),
        !any_builder.is_empty(),
    )?;
    module_items.extend(any_reader);
    module_items.extend(any_builder);
    module_items.extend(downcasts);

    Ok(Branch(vec![
        BlankLine,
        Line(format!("pub mod {} {{", module_name(node_name))),
        indent(newtype_type_id_line(node_id)),
        indent(module_items),
        line("}"),
    ]))
}

// Emits `impl<'a> <newtype>::Reader<'a> for <instance>::Reader<'a>` at a use site, giving the
// stamped group's per-instance module the newtype's identity. Each method delegates to the
// inherent accessor (inherent methods win over trait methods in method resolution, so this is
// not recursive), which keeps offsets/defaults/pointer handling in one place.
fn generate_newtype_impl(
    ctx: &GeneratorContext,
    alias_id: u64,
    instance_id: u64,
) -> ::capnp::Result<FormattedText> {
    Ok(Branch(vec![
        generate_group_newtype_impl(ctx, alias_id, instance_id)?,
        generate_union_newtype_impl(ctx, alias_id, instance_id)?,
    ]))
}

fn generate_group_newtype_impl(
    ctx: &GeneratorContext,
    alias_id: u64,
    instance_id: u64,
) -> ::capnp::Result<FormattedText> {
    use capnp::schema_capnp::*;
    let Some(template_id) = group_newtype_template_id(ctx, alias_id)? else {
        return Ok(Branch(vec![]));
    };
    let node::Struct(tmpl) = ctx.node_map[&template_id].which()? else {
        return Ok(Branch(vec![]));
    };
    let node::Struct(instance) = ctx.node_map[&instance_id].which()? else {
        return Ok(Branch(vec![]));
    };

    // An incomplete `@[...]` mapping omits trailing fields from the instance; those have no
    // inherent accessor to delegate to, so skip the trait for such a use site until the erased
    // carrier (which reads defaults) lands. Index the instance's fields by name so nested members
    // can find their per-instance group node.
    let mut instance_fields = ::std::collections::HashMap::new();
    for field in instance.get_fields()? {
        instance_fields.insert(field.get_name()?.to_str()?.to_string(), field);
    }

    let mut trait_ok = true;
    let mut reader_items = Vec::new();
    let mut builder_items = Vec::new();
    for field in tmpl.get_fields()? {
        let raw_name = field.get_name()?.to_str()?;
        let Some(inst_field) = instance_fields.get(raw_name) else {
            // Unmapped leaf (incomplete `@[...]`): a scalar reads its default and its setter
            // panics -- matching C++'s default read + "not mapped" assert. Anything else can't be
            // synthesized in the concrete trait here, so skip just the trait for this use site --
            // the erased `AnyReader` (via the offset table's sentinels) still reads it.
            if is_scalar_data_field(&field)? {
                let field::Slot(s) = field.which()? else {
                    trait_ok = false;
                    continue;
                };
                let dflt = prim_default_value(&s.get_default_value()?)?;
                let not_mapped =
                    format!("panic!(\"field '{raw_name}' is not mapped at this use site\")");
                for m in newtype_trait_methods(ctx, &field, true, true)? {
                    reader_items.push(Line(format!("fn {} {{ {dflt} }}", m.signature)));
                }
                for m in newtype_trait_methods(ctx, &field, false, true)? {
                    let body = if m.call_name.starts_with("get_") {
                        dflt.clone()
                    } else if m.call_args.is_empty() {
                        not_mapped.clone()
                    } else if m.call_args.contains(',') {
                        format!("let _ = ({}); {not_mapped}", m.call_args)
                    } else {
                        // Consume the arg so the panic-only body doesn't warn as unused.
                        format!("let _ = {}; {not_mapped}", m.call_args)
                    };
                    builder_items.push(Line(format!("fn {} {{ {body} }}", m.signature)));
                }
            } else {
                trait_ok = false;
            }
            continue;
        };
        // Delegate to the inherent accessor: inherent methods win over trait methods in method
        // resolution, so this forwards rather than recurses, keeping offsets/defaults in one place.
        if let field::Group(_) = field.which()? {
            let field::Group(inst_group) = inst_field.which()? else {
                return Ok(Branch(vec![]));
            };
            let name = camel_to_snake_case(raw_name);
            let assoc = capitalize_first_letter(raw_name);
            let inst_mod = ctx.get_qualified_module(inst_group.get_type_id());
            reader_items.push(Line(format!("type {assoc} = {inst_mod}::Reader<'a>;")));
            reader_items.push(Line(format!(
                "fn get_{name}(&self) -> Self::{assoc} {{ (*self).get_{name}() }}"
            )));
            builder_items.push(Line(format!("type {assoc} = {inst_mod}::Builder<'a>;")));
            builder_items.push(Line(format!(
                "fn get_{name}(self) -> Self::{assoc} {{ self.get_{name}() }}"
            )));
            builder_items.push(Line(format!(
                "fn init_{name}(self) -> Self::{assoc} {{ self.init_{name}() }}"
            )));
        } else {
            for m in newtype_trait_methods(ctx, &field, true, true)? {
                let recv = if m.deref_self { "(*self)" } else { "self" };
                reader_items.push(Line(format!(
                    "fn {} {{ {recv}.{}({}) }}",
                    m.signature, m.call_name, m.call_args
                )));
            }
            for m in newtype_trait_methods(ctx, &field, false, true)? {
                let recv = if m.deref_self { "(*self)" } else { "self" };
                builder_items.push(Line(format!(
                    "fn {} {{ {recv}.{}({}) }}",
                    m.signature, m.call_name, m.call_args
                )));
            }
        }
    }

    let reader_methods = reader_items;
    let builder_methods = builder_items;
    let trait_path = ctx.get_qualified_module(alias_id);
    let concrete = ctx.get_qualified_module(instance_id);

    // Erased-carrier wiring: a per-use-site offset table (recursively over nested members) plus
    // `as_any()` on the concrete reader -- through the public `IntoInternalStructReader`, since the
    // inner field is private at this impl site.
    let mut any_items = Vec::new();
    {
        let mut offsets = Vec::new();
        collect_leaf_offsets(ctx, template_id, instance_id, &mut offsets)?;
        let n = offsets.len();
        let table = use_site_offsets_name(ctx, instance_id)?;
        any_items.push(BlankLine);
        any_items.push(Line(format!(
            "static {table}: [u32; {n}] = [{}];",
            offsets.join(", ")
        )));
        any_items.push(Line(format!("impl<'a> {concrete}::Reader<'a> {{")));
        any_items.push(indent(Line(fmt!(ctx,
            "pub fn as_any(self) -> {trait_path}::AnyReader<'a> {{ {trait_path}::AnyReader::new({capnp}::traits::IntoInternalStructReader::into_internal_struct_reader(self), &{table}) }}"
        ))));
        any_items.push(line("}"));
        any_items.push(Line(format!("impl<'a> {concrete}::Builder<'a> {{")));
        any_items.push(indent(Line(fmt!(ctx,
            "pub fn as_any(self) -> {trait_path}::AnyBuilder<'a> {{ {trait_path}::AnyBuilder::new({capnp}::traits::IntoInternalStructBuilder::into_internal_struct_builder(self), &{table}) }}"
        ))));
        any_items.push(line("}"));
    }

    // The concrete trait impls require every leaf mappable (see `trait_ok`); the erased carrier
    // (`any_items`) is always emitted -- it reads unmapped leaves as defaults via the offset table.
    let mut out = Vec::new();
    if trait_ok {
        out.push(BlankLine);
        out.push(Line(format!(
            "impl<'a> {trait_path}::Reader<'a> for {concrete}::Reader<'a> {{"
        )));
        out.push(indent(reader_methods));
        out.push(line("}"));
        out.push(BlankLine);
        out.push(Line(format!(
            "impl<'a> {trait_path}::Builder<'a> for {concrete}::Builder<'a> {{"
        )));
        out.push(indent(builder_methods));
        out.push(line("}"));
    }
    out.push(Branch(any_items));
    Ok(Branch(out))
}

// The `Which` enum variants for a union newtype and whether any arm payload borrows (so the enum
// needs a `<'a>`). Payload types come straight from the arm getter, so they match the per-instance
// `Which` the impl maps from.
// The `<...>` on a union newtype's `Which`: an optional `'a` (when a slot arm's payload borrows)
// followed by one type parameter per group arm (`params`).
fn union_which_generics(needs_lifetime: bool, params: &[String]) -> String {
    let mut all = Vec::new();
    if needs_lifetime {
        all.push("'a".to_string());
    }
    all.extend(params.iter().cloned());
    if all.is_empty() {
        String::new()
    } else {
        format!("<{}>", all.join(", "))
    }
}

// Emits `pub mod <name> { pub enum Which<...> {...} pub trait Reader<'a> {...} pub trait Builder }`
// for a union newtype. A slot arm has a concrete `Which` payload; a group arm (a nested newtype) is
// a `Which` type parameter backed by an associated type bounded by the arm's trait.
fn generate_union_newtype_trait(
    ctx: &GeneratorContext,
    node_id: u64,
    node_name: &str,
) -> ::capnp::Result<FormattedText> {
    use capnp::schema_capnp::*;
    let Some(template_id) = union_newtype_template_id(ctx, node_id)? else {
        return Ok(Branch(vec![]));
    };
    let node::Struct(tmpl) = ctx.node_map[&template_id].which()? else {
        return Ok(Branch(vec![]));
    };

    let mut variants = Vec::new();
    let mut group_params = Vec::new();
    let mut reader_assoc = Vec::new();
    let mut reader_methods = Vec::new();
    let mut builder_assoc = Vec::new();
    let mut builder_methods = Vec::new();
    let mut needs_lifetime = false;
    for field in tmpl.get_fields()? {
        let variant = capitalize_first_letter(field.get_name()?.to_str()?);
        let name = camel_to_snake_case(field.get_name()?.to_str()?);
        if let field::Group(_) = field.which()? {
            let nested = ctx.get_qualified_module(field.get_type_id());
            variants.push(Line(format!("{variant}({variant}),")));
            group_params.push(variant.clone());
            reader_assoc.push(Line(format!("type {variant}: {nested}::Reader<'a>;")));
            builder_assoc.push(Line(format!("type {variant}: {nested}::Builder<'a>;")));
            builder_methods.push(Line(format!("fn init_{name}(self) -> Self::{variant};")));
        } else {
            let (payload, _, _) = getter_text(ctx, &field, true, false)?;
            if let field::Slot(s) = field.which()? {
                if s.get_type()?.is_pointer()? {
                    needs_lifetime = true;
                }
            }
            variants.push(Line(format!("{variant}({payload}),")));
            for m in newtype_trait_methods(ctx, &field, true, false)? {
                reader_methods.push(Line(format!("fn {};", m.signature)));
            }
            for m in newtype_trait_methods(ctx, &field, false, false)? {
                builder_methods.push(Line(format!("fn {};", m.signature)));
            }
        }
    }

    let which_generics = union_which_generics(needs_lifetime, &group_params);
    let self_params: Vec<String> = group_params.iter().map(|p| format!("Self::{p}")).collect();
    let which_ret = union_which_generics(needs_lifetime, &self_params);

    let mut reader_items = reader_assoc;
    reader_items.push(Line(format!(
        "fn which(&self) -> ::core::result::Result<Which{which_ret}, ::capnp::NotInSchema>;"
    )));
    reader_items.extend(reader_methods);
    let mut builder_items = builder_assoc;
    builder_items.extend(builder_methods);

    let mut module_items = vec![
        Branch(vec![
            Line(format!("pub enum Which{which_generics} {{")),
            indent(variants),
            line("}"),
        ]),
        line("pub trait Reader<'a> {"),
        indent(reader_items),
        line("}"),
        line("pub trait Builder<'a> {"),
        indent(builder_items),
        line("}"),
    ];
    let any_reader = union_any_reader_items(ctx, template_id)?;
    let any_builder = union_any_builder_items(ctx, template_id)?;
    let downcasts = any_downcast_impls(
        ctx,
        template_id,
        true,
        !any_reader.is_empty(),
        !any_builder.is_empty(),
    )?;
    module_items.extend(any_reader);
    module_items.extend(any_builder);
    module_items.extend(downcasts);

    Ok(Branch(vec![
        BlankLine,
        Line(format!("pub mod {} {{", module_name(node_name))),
        indent(newtype_type_id_line(node_id)),
        indent(module_items),
        line("}"),
    ]))
}

// Impls the union newtype's Reader/Builder traits for a use site. `which()` maps the per-instance
// `Which` variants to the shared enum; the arm accessors delegate to the inherent methods (which
// carry the right discriminant offset).
fn generate_union_newtype_impl(
    ctx: &GeneratorContext,
    alias_id: u64,
    instance_id: u64,
) -> ::capnp::Result<FormattedText> {
    use capnp::schema_capnp::*;
    let Some(template_id) = union_newtype_template_id(ctx, alias_id)? else {
        return Ok(Branch(vec![]));
    };
    let node::Struct(tmpl) = ctx.node_map[&template_id].which()? else {
        return Ok(Branch(vec![]));
    };
    let node::Struct(instance) = ctx.node_map[&instance_id].which()? else {
        return Ok(Branch(vec![]));
    };

    let mut instance_fields = ::std::collections::HashMap::new();
    for field in instance.get_fields()? {
        instance_fields.insert(field.get_name()?.to_str()?.to_string(), field);
    }

    let trait_path = ctx.get_qualified_module(alias_id);
    let concrete = ctx.get_qualified_module(instance_id);

    let mut which_arms = Vec::new();
    let mut group_params = Vec::new();
    let mut reader_assoc = Vec::new();
    let mut reader_methods = Vec::new();
    let mut builder_assoc = Vec::new();
    let mut builder_methods = Vec::new();
    let mut needs_lifetime = false;
    for field in tmpl.get_fields()? {
        let raw_name = field.get_name()?.to_str()?;
        let Some(inst_field) = instance_fields.get(raw_name) else {
            return Ok(Branch(vec![]));
        };
        let variant = capitalize_first_letter(raw_name);
        let name = camel_to_snake_case(raw_name);
        which_arms.push(Line(format!(
            "{concrete}::Which::{variant}(x) => {trait_path}::Which::{variant}(x),"
        )));
        if let field::Group(_) = field.which()? {
            let field::Group(inst_group) = inst_field.which()? else {
                return Ok(Branch(vec![]));
            };
            let inst_mod = ctx.get_qualified_module(inst_group.get_type_id());
            group_params.push(variant.clone());
            reader_assoc.push(Line(format!("type {variant} = {inst_mod}::Reader<'a>;")));
            builder_assoc.push(Line(format!("type {variant} = {inst_mod}::Builder<'a>;")));
            builder_methods.push(Line(format!(
                "fn init_{name}(self) -> Self::{variant} {{ self.init_{name}() }}"
            )));
        } else {
            if let field::Slot(s) = field.which()? {
                if s.get_type()?.is_pointer()? {
                    needs_lifetime = true;
                }
            }
            for m in newtype_trait_methods(ctx, &field, true, false)? {
                let recv = if m.deref_self { "(*self)" } else { "self" };
                reader_methods.push(Line(format!(
                    "fn {} {{ {recv}.{}({}) }}",
                    m.signature, m.call_name, m.call_args
                )));
            }
            for m in newtype_trait_methods(ctx, &field, false, false)? {
                let recv = if m.deref_self { "(*self)" } else { "self" };
                builder_methods.push(Line(format!(
                    "fn {} {{ {recv}.{}({}) }}",
                    m.signature, m.call_name, m.call_args
                )));
            }
        }
    }
    let self_params: Vec<String> = group_params.iter().map(|p| format!("Self::{p}")).collect();
    let which_ret = union_which_generics(needs_lifetime, &self_params);

    let which_method = Branch(vec![
        Line(format!(
            "fn which(&self) -> ::core::result::Result<{trait_path}::Which{which_ret}, ::capnp::NotInSchema> {{"
        )),
        indent(vec![
            line("::core::result::Result::Ok(match (*self).which()? {"),
            indent(which_arms),
            line("})"),
        ]),
        line("}"),
    ]);

    let mut reader_items = reader_assoc;
    reader_items.push(which_method);
    reader_items.extend(reader_methods);
    let mut builder_items = builder_assoc;
    builder_items.extend(builder_methods);

    // Erased-carrier wiring: the offset table plus a runtime discriminant offset, then `as_any()`.
    let mut offsets = Vec::new();
    collect_leaf_offsets(ctx, template_id, instance_id, &mut offsets)?;
    let n = offsets.len();
    let disc = instance.get_discriminant_offset();
    let table = use_site_offsets_name(ctx, instance_id)?;
    let any_items = vec![
        BlankLine,
        Line(format!(
            "static {table}: [u32; {n}] = [{}];",
            offsets.join(", ")
        )),
        Line(format!("impl<'a> {concrete}::Reader<'a> {{")),
        indent(Line(fmt!(ctx,
            "pub fn as_any(self) -> {trait_path}::AnyReader<'a> {{ {trait_path}::AnyReader::new({capnp}::traits::IntoInternalStructReader::into_internal_struct_reader(self), {disc}, &{table}) }}"
        ))),
        line("}"),
        Line(format!("impl<'a> {concrete}::Builder<'a> {{")),
        indent(Line(fmt!(ctx,
            "pub fn as_any(self) -> {trait_path}::AnyBuilder<'a> {{ {trait_path}::AnyBuilder::new({capnp}::traits::IntoInternalStructBuilder::into_internal_struct_builder(self), {disc}, &{table}) }}"
        ))),
        line("}"),
    ];

    Ok(Branch(vec![
        BlankLine,
        Line(format!(
            "impl<'a> {trait_path}::Reader<'a> for {concrete}::Reader<'a> {{"
        )),
        indent(reader_items),
        line("}"),
        BlankLine,
        Line(format!(
            "impl<'a> {trait_path}::Builder<'a> for {concrete}::Builder<'a> {{"
        )),
        indent(builder_items),
        line("}"),
        Branch(any_items),
    ]))
}

// Emits `pub mod <name> { pub type Reader ...; Builder; Owned }` for a scalar newtype (`type Uuid
// = Data`, `type Age = UInt16`) so use sites can name the alias. A value newtype's aliases carry
// no lifetime; a pointer newtype's Reader/Builder keep `<'a>`. Inline group/union newtypes (which
// get a trait instead) and aliases of a pre-existing struct/interface are skipped here.
fn generate_scalar_newtype_alias(
    ctx: &GeneratorContext,
    node_id: u64,
    node_name: &str,
    t: schema_capnp::type_::Reader,
) -> ::capnp::Result<FormattedText> {
    use capnp::schema_capnp::*;
    if newtype_template_id(ctx, node_id)?.is_some() {
        return Ok(Branch(vec![]));
    }
    if matches!(t.which()?, type_::Struct(_) | type_::Interface(_)) {
        return Ok(Branch(vec![]));
    }
    let module = module_name(node_name);
    let items = if t.is_pointer()? {
        vec![
            Line(format!(
                "pub type Reader<'a> = {};",
                t.type_string(ctx, Leaf::Reader("'a"))?
            )),
            Line(format!(
                "pub type Builder<'a> = {};",
                t.type_string(ctx, Leaf::Builder("'a"))?
            )),
            Line(format!(
                "pub type Owned = {};",
                t.type_string(ctx, Leaf::Owned)?
            )),
        ]
    } else {
        let v = t.type_string(ctx, Leaf::Reader(""))?;
        vec![
            Line(format!("pub type Reader = {v};")),
            Line(format!("pub type Builder = {v};")),
            Line(format!("pub type Owned = {v};")),
        ]
    };
    Ok(Branch(vec![
        BlankLine,
        Line(format!("pub mod {module} {{")),
        indent(newtype_type_id_line(node_id)),
        indent(items),
        line("}"),
    ]))
}

fn generate_node(
    ctx: &GeneratorContext,
    node_id: u64,
    node_name: &str,
) -> ::capnp::Result<FormattedText> {
    use capnp::schema_capnp::*;

    let mut output: Vec<FormattedText> = Vec::new();
    let mut nested_output: Vec<FormattedText> = Vec::new();

    let node_reader = &ctx.node_map[&node_id];
    let nested_nodes = node_reader.get_nested_nodes()?;
    for nested_node in nested_nodes {
        let id = nested_node.get_id();
        nested_output.push(generate_node(ctx, id, ctx.get_last_name(id)?)?);
    }

    match node_reader.which()? {
        node::Type(Ok(t)) => {
            output.push(generate_newtype_trait(ctx, node_id, node_name)?);
            output.push(generate_scalar_newtype_alias(ctx, node_id, node_name, t)?);
        }
        node::Type(Err(e)) => {
            return Err(Error::failed(format!("error reading node type: {e}")));
        }
        node::File(()) => {
            output.push(Branch(nested_output));
        }
        node::Struct(struct_reader) => {
            let params = node_reader.parameters_texts(ctx);
            output.push(BlankLine);

            let is_generic = node_reader.get_is_generic();
            if is_generic {
                output.push(Line(format!(
                    "pub mod {} {{ /* {} */",
                    node_name,
                    params.expanded_list.join(",")
                )));
            } else {
                output.push(Line(format!("pub mod {node_name} {{")));
            }
            let bracketed_params = if params.params.is_empty() {
                "".to_string()
            } else {
                format!("<{}>", params.params)
            };

            let mut preamble = Vec::new();
            let mut builder_members = Vec::new();
            let mut reader_members = Vec::new();
            let mut union_fields = Vec::new();
            let mut which_enums = Vec::new();
            let mut pipeline_impl_interior = Vec::new();
            let mut private_mod_interior = Vec::new();

            let data_size = struct_reader.get_data_word_count();
            let pointer_size = struct_reader.get_pointer_count();
            let discriminant_count = struct_reader.get_discriminant_count();
            let discriminant_offset = struct_reader.get_discriminant_offset();

            private_mod_interior.push(crate::pointer_constants::node_word_array_declaration(
                ctx,
                "ENCODED_NODE",
                *node_reader,
                crate::pointer_constants::WordArrayDeclarationOptions { pub_crate: true },
            )?);

            private_mod_interior.push(generate_get_field_types(ctx, *node_reader)?);
            private_mod_interior.push(generate_get_annotation_types(ctx, *node_reader)?);

            // `static` instead of `const` so that this has a fixed memory address
            // and we can check equality of `RawStructSchema` values by comparing pointers.
            let field_newtypes = generate_field_newtypes(ctx, *node_reader)?;
            let mut raw_schema_end = ")".to_string();
            if field_newtypes.is_some() {
                raw_schema_end += ".with_field_newtypes(FIELD_NEWTYPES)";
            }
            if let Some(any_layout) = use_site_any_layout(ctx, *node_reader)? {
                raw_schema_end += &any_layout;
            }
            raw_schema_end += ";";
            private_mod_interior.push(Branch(vec![
                Line(fmt!(ctx, "pub(crate) static ARENA: {capnp}::private::arena::GeneratedCodeArena = {capnp}::private::arena::GeneratedCodeArena::new(&ENCODED_NODE);")),
                Line(fmt!(ctx,"pub(crate) static RAW_SCHEMA: {capnp}::introspect::RawStructSchema = {capnp}::introspect::RawStructSchema::new(")),
                indent(vec![
                    Line("&ARENA,".into()),
                    Line("NONUNION_MEMBERS,".into()),
                    Line("MEMBERS_BY_DISCRIMINANT,".into()),
                    Line("MEMBERS_BY_NAME".into()),
                ]),
                Line(raw_schema_end),
            ]));
            if let Some(field_newtypes) = field_newtypes {
                private_mod_interior.push(field_newtypes);
            }

            private_mod_interior.push(generate_members_by_discriminant(*node_reader)?);
            private_mod_interior.push(generate_members_by_name(*node_reader)?);

            let mut has_pointer_field = false;
            let fields = struct_reader.get_fields()?;
            for field in fields {
                let name = get_field_name(field)?;
                let styled_name = camel_to_snake_case(name);

                let discriminant_value = field.get_discriminant_value();
                let is_union_field = discriminant_value != field::NO_DISCRIMINANT;

                match field.which()? {
                    field::Slot(s) => match s.get_type()?.which()? {
                        type_::Text(())
                        | type_::Data(())
                        | type_::List(_)
                        | type_::Struct(_)
                        | type_::Interface(_)
                        | type_::AnyPointer(_) => has_pointer_field = true,
                        _ => (),
                    },
                    field::Group(_) => has_pointer_field = true,
                }

                if !is_union_field {
                    pipeline_impl_interior.push(generate_pipeline_getter(ctx, field)?);
                    let (ty, get, default_decl) = getter_text(ctx, &field, true, true)?;
                    if let Some(default) = default_decl {
                        private_mod_interior.push(default.clone());
                    }
                    reader_members.push(Branch(vec![
                        line("#[inline]"),
                        Line(format!("pub fn get_{styled_name}(self) {ty} {{")),
                        indent(get),
                        line("}"),
                    ]));

                    let (ty_b, get_b, _) = getter_text(ctx, &field, false, true)?;
                    builder_members.push(Branch(vec![
                        line("#[inline]"),
                        Line(format!("pub fn get_{styled_name}(self) {ty_b} {{")),
                        indent(get_b),
                        line("}"),
                    ]));
                } else {
                    union_fields.push(field);
                }

                builder_members.push(generate_setter(
                    ctx,
                    discriminant_offset,
                    &styled_name,
                    &field,
                )?);

                reader_members.push(generate_haser(
                    discriminant_offset,
                    &styled_name,
                    &field,
                    true,
                )?);
                builder_members.push(generate_haser(
                    discriminant_offset,
                    &styled_name,
                    &field,
                    false,
                )?);

                if let Ok(field::Group(group)) = field.which() {
                    let id = group.get_type_id();
                    let text = generate_node(ctx, id, ctx.get_last_name(id)?)?;
                    nested_output.push(text);

                    // If this group is a stamped inline newtype, give its per-instance module the
                    // newtype's semantic trait.
                    let alias_id = field.get_type_id();
                    if alias_id != 0 {
                        nested_output.push(generate_newtype_impl(ctx, alias_id, id)?);
                    }
                }
            }

            if discriminant_count > 0 {
                let (which_enums1, union_getter, typedef, mut default_decls) =
                    generate_union(ctx, discriminant_offset, &union_fields, true, &params)?;
                which_enums.push(which_enums1);
                which_enums.push(typedef);
                reader_members.push(union_getter);

                private_mod_interior.append(&mut default_decls);

                let (_, union_getter, typedef, _) =
                    generate_union(ctx, discriminant_offset, &union_fields, false, &params)?;
                which_enums.push(typedef);
                builder_members.push(union_getter);

                let mut reexports = String::new();
                reexports.push_str("pub use self::Which::{");
                let mut whichs = Vec::new();
                for f in &union_fields {
                    whichs.push(capitalize_first_letter(get_field_name(*f)?));
                }
                reexports.push_str(&whichs.join(","));
                reexports.push_str("};");
                preamble.push(Line(reexports));
                preamble.push(BlankLine);
            }

            let builder_struct_size =
                Branch(vec![
                    Line(fmt!(ctx,"impl <{0}> {capnp}::traits::HasStructSize for Builder<'_,{0}> {1} {{",
                                 params.params, params.where_clause)),
                                 indent(Line(
                        fmt!(ctx,"const STRUCT_SIZE: {capnp}::private::layout::StructSize = {capnp}::private::layout::StructSize {{ data: {}, pointers: {} }};", data_size as usize, pointer_size as usize))),
                   line("}")]);

            private_mod_interior.push(Line(format!(
                "pub(crate) const TYPE_ID: u64 = {};",
                format_u64(node_id)
            )));

            let from_pointer_builder_impl =
                Branch(vec![
                    Line(fmt!(ctx,"impl <'a,{0}> {capnp}::traits::FromPointerBuilder<'a> for Builder<'a,{0}> {1} {{", params.params, params.where_clause)),
                    indent(vec![
                        Line(fmt!(ctx,"fn init_pointer(builder: {capnp}::private::layout::PointerBuilder<'a>, _size: u32) -> Self {{")),
                        indent(Line(fmt!(ctx,"builder.init_struct(<Self as {capnp}::traits::HasStructSize>::STRUCT_SIZE).into()"))),
                        line("}"),
                        Line(fmt!(ctx,"fn get_from_pointer(builder: {capnp}::private::layout::PointerBuilder<'a>, default: ::core::option::Option<&'a [{capnp}::Word]>) -> {capnp}::Result<Self> {{")),
                        indent(Line(fmt!(ctx,"::core::result::Result::Ok(builder.get_struct(<Self as {capnp}::traits::HasStructSize>::STRUCT_SIZE, default)?.into())"))),
                        line("}")
                    ]),
                    line("}"),
                    BlankLine]);

            let accessors = vec![
                Branch(preamble),
                (if !is_generic {
                    Branch(vec![
                        Line("#[derive(Copy, Clone)]".into()),
                        line("pub struct Owned(());"),
                        Line(fmt!(ctx,"impl {capnp}::introspect::Introspect for Owned {{ fn introspect() -> {capnp}::introspect::Type {{ {capnp}::introspect::TypeVariant::Struct({capnp}::introspect::RawBrandedStructSchema {{ generic: &_private::RAW_SCHEMA, field_types: _private::get_field_types, annotation_types: _private::get_annotation_types, type_id: ::core::any::TypeId::of::<Owned>() }}).into() }} }}")),
                        Line(fmt!(ctx, "impl {capnp}::traits::Owned for Owned {{ type Reader<'a> = Reader<'a>; type Builder<'a> = Builder<'a>; }}")),
                        Line(fmt!(ctx,"impl {capnp}::traits::OwnedStruct for Owned {{ type Reader<'a> = Reader<'a>; type Builder<'a> = Builder<'a>; }}")),
                        Line(fmt!(ctx,"impl {capnp}::traits::Pipelined for Owned {{ type Pipeline = Pipeline; }}"))
                    ])
                } else {
                    Branch(vec![
                        Line("#[derive(Copy, Clone)]".into()),
                        Line(format!("pub struct Owned<{}> {{", params.params)),
                            indent(Line(params.phantom_data_type.clone())),
                        line("}"),
                        Line(fmt!(ctx,"impl <{0}> {capnp}::introspect::Introspect for Owned <{0}> {1} {{ fn introspect() -> {capnp}::introspect::Type {{ {capnp}::introspect::TypeVariant::Struct({capnp}::introspect::RawBrandedStructSchema {{ generic: &_private::RAW_SCHEMA, field_types: _private::get_field_types::<{0}>, annotation_types: _private::get_annotation_types::<{0}>, type_id: ::core::any::TypeId::of::<Owned<{0}>>() }}).into() }} }}",
                            params.params, params.where_clause)),
                        Line(fmt!(ctx,"impl <{0}> {capnp}::traits::Owned for Owned <{0}> {1} {{ type Reader<'a> = Reader<'a, {0}>; type Builder<'a> = Builder<'a, {0}>; }}",
                            params.params, params.where_clause)),
                        Line(fmt!(ctx,"impl <{0}> {capnp}::traits::OwnedStruct for Owned <{0}> {1} {{ type Reader<'a> = Reader<'a, {0}>; type Builder<'a> = Builder<'a, {0}>; }}",
                            params.params, params.where_clause)),
                        Line(fmt!(ctx,"impl <{0}> {capnp}::traits::Pipelined for Owned<{0}> {1} {{ type Pipeline = Pipeline{2}; }}",
                            params.params, params.where_clause, bracketed_params)),
                    ])
                }),
                BlankLine,
                (if !is_generic {
                    Line(fmt!(ctx,"pub struct Reader<'a> {{ reader: {capnp}::private::layout::StructReader<'a> }}"))
                } else {
                    Branch(vec![
                        Line(format!("pub struct Reader<'a,{}> {} {{", params.params, params.where_clause)),
                        indent(vec![
                            Line(fmt!(ctx,"reader: {capnp}::private::layout::StructReader<'a>,")),
                            Line(params.phantom_data_type.clone()),
                        ]),
                        line("}")
                    ])
                }),
                // Manually implement Copy/Clone because `derive` only kicks in if all of
                // the parameters are known to implement Copy/Clone.
                Branch(vec![
                    Line(format!("impl <{0}> ::core::marker::Copy for Reader<'_,{0}> {1} {{}}",
                                 params.params, params.where_clause)),
                    Line(format!("impl <{0}> ::core::clone::Clone for Reader<'_,{0}> {1} {{",
                                 params.params, params.where_clause)),
                    indent(Line("fn clone(&self) -> Self { *self }".into())),
                    Line("}".into())]),
                BlankLine,
                Branch(vec![
                        Line(fmt!(ctx,"impl <{0}> {capnp}::traits::HasTypeId for Reader<'_,{0}> {1} {{",
                            params.params, params.where_clause)),
                        indent(vec![line("const TYPE_ID: u64 = _private::TYPE_ID;")]),
                    line("}")]),
                Line(fmt!(ctx,"impl <'a,{0}> ::core::convert::From<{capnp}::private::layout::StructReader<'a>> for Reader<'a,{0}> {1} {{",
                            params.params, params.where_clause)),
                indent(vec![
                    Line(fmt!(ctx,"fn from(reader: {capnp}::private::layout::StructReader<'a>) -> Self {{")),
                    indent(Line(format!("Self {{ reader, {} }}", params.phantom_data_value))),
                    line("}")
                ]),
                line("}"),
                BlankLine,
                Line(fmt!(ctx,"impl <'a,{0}> ::core::convert::From<Reader<'a,{0}>> for {capnp}::dynamic_value::Reader<'a> {1} {{",
                            params.params, params.where_clause)),
                indent(vec![
                    Line(format!("fn from(reader: Reader<'a,{0}>) -> Self {{", params.params)),
                    indent(Line(fmt!(ctx,"Self::Struct({capnp}::dynamic_struct::Reader::new(reader.reader, {capnp}::schema::StructSchema::new({capnp}::introspect::RawBrandedStructSchema {{ generic: &_private::RAW_SCHEMA, field_types: _private::get_field_types::<{0}>, annotation_types: _private::get_annotation_types::<{0}>, type_id: ::core::any::TypeId::of::<Owned<{0}>>()}})))", params.params))),
                    line("}")
                ]),
                line("}"),
                BlankLine,
                Line(format!("impl <{0}> ::core::fmt::Debug for Reader<'_,{0}> {1} {{",
                            params.params, params.where_clause)),
                indent(vec![
                    Line("fn fmt(&self, f: &mut ::core::fmt::Formatter<'_>) -> ::core::result::Result<(), ::core::fmt::Error> {".into()),
                    indent(Line(fmt!(ctx,"core::fmt::Debug::fmt(&::core::convert::Into::<{capnp}::dynamic_value::Reader<'_>>::into(*self), f)"))),
                    line("}")
                ]),
                line("}"),

                BlankLine,

                Line(fmt!(ctx,"impl <'a,{0}> {capnp}::traits::FromPointerReader<'a> for Reader<'a,{0}> {1} {{",
                    params.params, params.where_clause)),
                indent(vec![
                    Line(fmt!(ctx,"fn get_from_pointer(reader: &{capnp}::private::layout::PointerReader<'a>, default: ::core::option::Option<&'a [{capnp}::Word]>) -> {capnp}::Result<Self> {{")),
                    indent(line("::core::result::Result::Ok(reader.get_struct(default)?.into())")),
                    line("}")
                ]),
                line("}"),
                BlankLine,
                Line(fmt!(ctx,"impl <'a,{0}> {capnp}::traits::IntoInternalStructReader<'a> for Reader<'a,{0}> {1} {{",
                            params.params, params.where_clause)),
                indent(vec![
                    Line(fmt!(ctx,"fn into_internal_struct_reader(self) -> {capnp}::private::layout::StructReader<'a> {{")),
                    indent(line("self.reader")),
                    line("}")
                ]),
                line("}"),
                BlankLine,
                Line(fmt!(ctx,"impl <'a,{0}> {capnp}::traits::Imbue<'a> for Reader<'a,{0}> {1} {{",
                    params.params, params.where_clause)),
                indent(vec![
                    Line(fmt!(ctx,"fn imbue(&mut self, cap_table: &'a {capnp}::private::layout::CapTable) {{")),
                    indent(Line(fmt!(ctx,"self.reader.imbue({capnp}::private::layout::CapTableReader::from_ref(cap_table))"))),
                    line("}")
                ]),
                line("}"),
                BlankLine,
                if has_pointer_field { // we do this to keep clippy happy
                    Line(format!("impl <'a,{0}> Reader<'a,{0}> {1} {{", params.params, params.where_clause))
                } else {
                    Line(format!("impl <{0}> Reader<'_,{0}> {1} {{", params.params, params.where_clause))
                },
                indent(vec![
                        Line(format!("pub fn reborrow(&self) -> Reader<'_,{}> {{",params.params)),
                        indent(line("Self { .. *self }")),
                        line("}"),
                        BlankLine,
                        Line(fmt!(ctx,"pub fn total_size(&self) -> {capnp}::Result<{capnp}::MessageSize> {{")),
                        indent(line("self.reader.total_size()")),
                        line("}")]),
                indent(reader_members),
                line("}"),
                BlankLine,
                (if !is_generic {
                    Line(fmt!(ctx,"pub struct Builder<'a> {{ builder: {capnp}::private::layout::StructBuilder<'a> }}"))
                } else {
                    Branch(vec![
                        Line(format!("pub struct Builder<'a,{}> {} {{",
                                     params.params, params.where_clause)),
                            indent(vec![
                            Line(fmt!(ctx, "builder: {capnp}::private::layout::StructBuilder<'a>,")),
                            Line(params.phantom_data_type.clone()),
                        ]),
                        line("}")
                    ])
                }),
                builder_struct_size,
                Branch(vec![
                    Line(fmt!(ctx,"impl <{0}> {capnp}::traits::HasTypeId for Builder<'_,{0}> {1} {{",
                                 params.params, params.where_clause)),
                    indent(vec![
                        line("const TYPE_ID: u64 = _private::TYPE_ID;")]),
                    line("}")
                ]),
                Line(fmt!(ctx,
                    "impl <'a,{0}> ::core::convert::From<{capnp}::private::layout::StructBuilder<'a>> for Builder<'a,{0}> {1} {{",
                    params.params, params.where_clause)),
                indent(vec![
                        Line(fmt!(ctx,"fn from(builder: {capnp}::private::layout::StructBuilder<'a>) -> Self {{")),
                        indent(Line(format!("Self {{ builder, {} }}", params.phantom_data_value))),
                        line("}")
                ]),
                line("}"),
                BlankLine,
                Line(fmt!(ctx,"impl <'a,{0}> {capnp}::traits::IntoInternalStructBuilder<'a> for Builder<'a,{0}> {1} {{",
                            params.params, params.where_clause)),
                indent(vec![
                    Line(fmt!(ctx,"fn into_internal_struct_builder(self) -> {capnp}::private::layout::StructBuilder<'a> {{")),
                    indent(line("self.builder")),
                    line("}")
                ]),
                line("}"),
                BlankLine,
                Line(fmt!(ctx,"impl <'a,{0}> ::core::convert::From<Builder<'a,{0}>> for {capnp}::dynamic_value::Builder<'a> {1} {{",
                            params.params, params.where_clause)),
                indent(vec![
                        Line(format!("fn from(builder: Builder<'a,{0}>) -> Self {{", params.params)),
                        indent(Line(fmt!(ctx,"Self::Struct({capnp}::dynamic_struct::Builder::new(builder.builder, {capnp}::schema::StructSchema::new({capnp}::introspect::RawBrandedStructSchema {{ generic: &_private::RAW_SCHEMA, field_types: _private::get_field_types::<{0}>, annotation_types: _private::get_annotation_types::<{0}>, type_id: ::core::any::TypeId::of::<Owned<{0}>>()}})))", params.params))),
                        line("}")
                ]),
                line("}"),
                BlankLine,

                Line(fmt!(ctx,"impl <'a,{0}> {capnp}::traits::ImbueMut<'a> for Builder<'a,{0}> {1} {{",
                             params.params, params.where_clause)),
                indent(vec![
                        Line(fmt!(ctx,"fn imbue_mut(&mut self, cap_table: &'a mut {capnp}::private::layout::CapTable) {{")),
                        indent(Line(fmt!(ctx,"self.builder.imbue({capnp}::private::layout::CapTableBuilder::from_ref(cap_table))"))),
                        line("}")]),
                line("}"),
                BlankLine,

                from_pointer_builder_impl,
                Line(fmt!(ctx,
                    "impl <{0}> {capnp}::traits::SetterInput<Owned<{0}>> for Reader<'_,{0}> {1} {{",
                    params.params, params.where_clause)),
                indent(Line(fmt!(ctx,"fn set_pointer_builder(mut pointer: {capnp}::private::layout::PointerBuilder<'_>, value: Self, canonicalize: bool) -> {capnp}::Result<()> {{ pointer.set_struct(&value.reader, canonicalize) }}"))),
                line("}"),
                BlankLine,
                Line(format!("impl <'a,{0}> Builder<'a,{0}> {1} {{", params.params, params.where_clause)),
                indent(vec![
                        Line(format!("pub fn into_reader(self) -> Reader<'a,{}> {{", params.params)),
                        indent(line("self.builder.into_reader().into()")),
                        line("}"),
                        Line(format!("pub fn reborrow(&mut self) -> Builder<'_,{}> {{", params.params)),
                        (if !is_generic {
                            indent(line("Builder { builder: self.builder.reborrow() }"))
                        } else {
                            indent(line("Builder { builder: self.builder.reborrow(), ..*self }"))
                        }),
                        line("}"),
                        Line(format!("pub fn reborrow_as_reader(&self) -> Reader<'_,{}> {{", params.params)),
                        indent(line("self.builder.as_reader().into()")),
                        line("}"),

                        BlankLine,
                        Line(fmt!(ctx,"pub fn total_size(&self) -> {capnp}::Result<{capnp}::MessageSize> {{")),
                        indent(line("self.builder.as_reader().total_size()")),
                        line("}")
                        ]),
                indent(builder_members),
                line("}"),
                BlankLine,
                (if is_generic {
                    Branch(vec![
                        Line(format!("pub struct Pipeline{bracketed_params} {{")),
                        indent(vec![
                            Line(fmt!(ctx,"_typeless: {capnp}::any_pointer::Pipeline,")),
                            Line(params.phantom_data_type),
                        ]),
                        line("}")
                    ])
                } else {
                    Line(fmt!(ctx,"pub struct Pipeline {{ _typeless: {capnp}::any_pointer::Pipeline }}"))
                }),
                Line(fmt!(ctx,"impl{bracketed_params} {capnp}::capability::FromTypelessPipeline for Pipeline{bracketed_params} {{")),
                indent(vec![
                        Line(fmt!(ctx,"fn new(typeless: {capnp}::any_pointer::Pipeline) -> Self {{")),
                        indent(Line(format!("Self {{ _typeless: typeless, {} }}", params.phantom_data_value))),
                        line("}")]),
                line("}"),
                Line(format!("impl{0} Pipeline{0} {1} {{", bracketed_params,
                             params.pipeline_where_clause)),
                indent(pipeline_impl_interior),
                line("}"),
                line("mod _private {"),
                indent(private_mod_interior),
                line("}"),
            ];

            output.push(indent(vec![
                Branch(accessors),
                Branch(which_enums),
                Branch(nested_output),
            ]));
            output.push(line("}"));
        }

        node::Enum(enum_reader) => {
            let last_name = ctx.get_last_name(node_id)?;
            let name_as_mod = module_name(last_name);
            output.push(BlankLine);

            let mut members = Vec::new();
            let mut match_branches = Vec::new();
            let enumerants = enum_reader.get_enumerants()?;
            for (ii, enumerant) in enumerants.into_iter().enumerate() {
                let enumerant = capitalize_first_letter(get_enumerant_name(enumerant)?);
                members.push(Line(format!("{enumerant} = {ii},")));
                match_branches.push(Line(format!(
                    "{ii} => ::core::result::Result::Ok(Self::{enumerant}),"
                )));
            }
            match_branches.push(Line(fmt!(
                ctx,
                "n => ::core::result::Result::Err({capnp}::NotInSchema(n)),"
            )));

            output.push(Branch(vec![
                line("#[repr(u16)]"),
                line("#[derive(Clone, Copy, Debug, PartialEq, Eq)]"),
                Line(format!("pub enum {last_name} {{")),
                indent(members),
                line("}"),
            ]));

            output.push(BlankLine);
            output.push(Branch(vec![
                Line(fmt!(ctx,
                    "impl {capnp}::introspect::Introspect for {last_name} {{"
                )),
                indent(Line(fmt!(ctx,
                    "fn introspect() -> {capnp}::introspect::Type {{ {capnp}::introspect::TypeVariant::Enum({capnp}::introspect::RawEnumSchema::new(&{0}::ARENA, {0}::get_annotation_types)).into() }}", name_as_mod))),
                Line("}".into()),
            ]));

            output.push(Branch(vec![
                Line(fmt!(ctx,"impl ::core::convert::From<{last_name}> for {capnp}::dynamic_value::Reader<'_> {{")),
                indent(Line(fmt!(ctx,
                    "fn from(e: {last_name}) -> Self {{ {capnp}::dynamic_value::Enum::new(e.into(), {capnp}::introspect::RawEnumSchema::new(&{0}::ARENA, {0}::get_annotation_types).into()).into() }}", name_as_mod ))),
                Line("}".into())
            ]));

            output.push(Branch(vec![
                Line(format!(
                    "impl ::core::convert::TryFrom<u16> for {last_name} {{"
                )),
                indent(Line(
                    fmt!(ctx,"type Error = {capnp}::NotInSchema;"),
                )),
                indent(vec![
                    Line(
                        format!("fn try_from(value: u16) -> ::core::result::Result<Self, <{last_name} as ::core::convert::TryFrom<u16>>::Error> {{")
                    ),
                    indent(vec![
                        line("match value {"),
                        indent(match_branches),
                        line("}"),
                    ]),
                    line("}"),
                ]),
                line("}"),
                Line(format!("impl From<{last_name}> for u16 {{")),
                indent(line("#[inline]")),
                indent(Line(format!(
                    "fn from(x: {last_name}) -> u16 {{ x as u16 }}"
                ))),
                line("}"),
            ]));

            output.push(Branch(vec![
                Line(fmt!(
                    ctx,
                    "impl {capnp}::traits::HasTypeId for {last_name} {{"
                )),
                indent(Line(format!(
                    "const TYPE_ID: u64 = {}u64;",
                    format_u64(node_id)
                ))),
                line("}"),
            ]));

            output.push(Branch(vec![
                Line(format!("mod {name_as_mod} {{")),
                Branch(vec![
                    crate::pointer_constants::node_word_array_declaration(
                        ctx,
                        "ENCODED_NODE",
                        *node_reader,
                        crate::pointer_constants::WordArrayDeclarationOptions { pub_crate: true },
                    )?,
                    generate_get_annotation_types(ctx, *node_reader)?,
                    Line(fmt!(ctx, "pub(crate) static ARENA: {capnp}::private::arena::GeneratedCodeArena = {capnp}::private::arena::GeneratedCodeArena::new(&ENCODED_NODE);")),
                ]),
                Line("}".into()),
            ]));
        }

        node::Interface(interface) => {
            let params = node_reader.parameters_texts(ctx);
            output.push(BlankLine);

            let is_generic = node_reader.get_is_generic();

            let names = &ctx.scope_map[&node_id];
            let mut client_impl_interior = Vec::new();
            let mut server_interior = Vec::new();
            let mut mod_interior = Vec::new();
            let mut dispatch_arms = Vec::new();
            let mut private_mod_interior = Vec::new();

            let bracketed_params = if params.params.is_empty() {
                "".to_string()
            } else {
                format!("<{}>", params.params)
            };

            private_mod_interior.push(Line(format!(
                "pub(crate) const TYPE_ID: u64 = {};",
                format_u64(node_id)
            )));

            mod_interior.push(line("#![allow(unused_variables)]"));

            let methods = interface.get_methods()?;
            for (ordinal, method) in methods.into_iter().enumerate() {
                let name = method.get_name()?.to_str()?;

                let param_id = method.get_param_struct_type();
                let param_node = &ctx.node_map[&param_id];
                let (param_scopes, params_ty_params) = if param_node.get_scope_id() == 0 {
                    let mut names = names.clone();
                    let local_name = module_name(&format!("{name}Params"));
                    nested_output.push(generate_node(ctx, param_id, &local_name)?);
                    names.push(local_name);
                    (names, params.params.clone())
                } else {
                    (
                        ctx.scope_map[&param_node.get_id()].clone(),
                        get_ty_params_of_brand(ctx, method.get_param_brand()?)?,
                    )
                };
                let param_type = do_branding(
                    ctx,
                    param_id,
                    method.get_param_brand()?,
                    Leaf::Owned,
                    &param_scopes.join("::"),
                )?;

                mod_interior.push(Line(fmt!(
                    ctx,
                    "pub type {}Params<{}> = {capnp}::capability::Params<{}>;",
                    capitalize_first_letter(name),
                    params_ty_params,
                    param_type
                )));

                let result_id = method.get_result_struct_type();
                if result_id != STREAM_RESULT_ID {
                    dispatch_arms.push(
                        Line(fmt!(ctx,
                                  "{ordinal} => {capnp}::capability::DispatchCallResult::new({capnp}::capability::Promise::from_future(<_T as Server{bracketed_params}>::{}(this, {capnp}::private::capability::internal_get_typed_params(params), {capnp}::private::capability::internal_get_typed_results(results))), false),",
                                  module_name(name))));

                    let result_node = &ctx.node_map[&result_id];
                    let (result_scopes, results_ty_params) = if result_node.get_scope_id() == 0 {
                        let mut names = names.clone();
                        let local_name = module_name(&format!("{name}Results"));
                        nested_output.push(generate_node(ctx, result_id, &local_name)?);
                        names.push(local_name);
                        (names, params.params.clone())
                    } else {
                        (
                            ctx.scope_map[&result_node.get_id()].clone(),
                            get_ty_params_of_brand(ctx, method.get_result_brand()?)?,
                        )
                    };
                    let result_type = do_branding(
                        ctx,
                        result_id,
                        method.get_result_brand()?,
                        Leaf::Owned,
                        &result_scopes.join("::"),
                    )?;
                    mod_interior.push(Line(fmt!(
                        ctx,
                        "pub type {}Results<{}> = {capnp}::capability::Results<{}>;",
                        capitalize_first_letter(name),
                        results_ty_params,
                        result_type
                    )));
                    server_interior.push(
                        Line(fmt!(ctx,
                                  "fn {}(self: {capnp}::capability::Rc<Self>, _: {}Params<{}>, _: {}Results<{}>) -> impl ::core::future::Future<Output = Result<(), {capnp}::Error>> + 'static {{ ::core::future::ready(Err({capnp}::Error::unimplemented(\"method {}::Server::{} not implemented\".to_string()))) }}",
                                  module_name(name),
                                  capitalize_first_letter(name), params_ty_params,
                                  capitalize_first_letter(name), results_ty_params,
                                  node_name, module_name(name)
                        )));

                    client_impl_interior.push(Line(fmt!(
                        ctx,
                        "pub fn {}_request(&self) -> {capnp}::capability::Request<{},{}> {{",
                        camel_to_snake_case(name),
                        param_type,
                        result_type
                    )));

                    client_impl_interior.push(indent(Line(format!(
                        "self.client.new_call(_private::TYPE_ID, {ordinal}, ::core::option::Option::None)"
                    ))));
                    client_impl_interior.push(line("}"));
                } else {
                    // It's a streaming method.
                    dispatch_arms.push(
                        Line(fmt!(ctx,
                                  "{ordinal} => {capnp}::capability::DispatchCallResult::new({capnp}::capability::Promise::from_future(<_T as Server{bracketed_params}>::{}(this, {capnp}::private::capability::internal_get_typed_params(params))), true),",

                                  module_name(name))));

                    server_interior.push(
                        Line(fmt!(ctx,
                                  "fn {}(self: {capnp}::capability::Rc<Self>, _: {}Params<{}>) -> impl ::core::future::Future<Output = Result<(), {capnp}::Error>> + 'static {{ ::core::future::ready(Err({capnp}::Error::unimplemented(\"method {}::Server::{} not implemented\".to_string()))) }}",
                                  module_name(name),
                                  capitalize_first_letter(name), params_ty_params,
                                  node_name, module_name(name)
                        )));
                    client_impl_interior.push(Line(fmt!(
                        ctx,
                        "pub fn {}_request(&self) -> {capnp}::capability::StreamingRequest<{}> {{",
                        camel_to_snake_case(name),
                        param_type
                    )));
                    client_impl_interior.push(indent(Line(format!(
                        "self.client.new_streaming_call(_private::TYPE_ID, {ordinal}, ::core::option::Option::None)"
                    ))));

                    client_impl_interior.push(line("}"));
                }

                method.get_annotations()?;
            }

            let mut base_dispatch_arms = Vec::new();

            let server_base = {
                let mut base_traits = Vec::new();

                fn find_super_interfaces<'a>(
                    interface: schema_capnp::node::interface::Reader<'a>,
                    all_extends: &mut Vec<
                        <schema_capnp::superclass::Owned as capnp::traits::OwnedStruct>::Reader<'a>,
                    >,
                    ctx: &GeneratorContext<'a>,
                ) -> ::capnp::Result<()> {
                    let extends = interface.get_superclasses()?;
                    for superclass in extends {
                        if let node::Interface(interface) =
                            ctx.node_map[&superclass.get_id()].which()?
                        {
                            find_super_interfaces(interface, all_extends, ctx)?;
                        }
                        all_extends.push(superclass);
                    }
                    Ok(())
                }

                let mut extends = Vec::new();
                find_super_interfaces(interface, &mut extends, ctx)?;
                for interface in &extends {
                    let type_id = interface.get_id();
                    let brand = interface.get_brand()?;
                    let the_mod = ctx.get_qualified_module(type_id);

                    base_dispatch_arms.push(Line(format!(
                        "0x{type_id:x} => {}::dispatch_call_internal(self.server, method_id, params, results),",
                        do_branding(
                            ctx, type_id, brand, Leaf::ServerDispatch, &the_mod)?)));
                    base_traits.push(do_branding(ctx, type_id, brand, Leaf::Server, &the_mod)?);
                }

                // Defining that the server itself should always be 'static makes
                // bounds easier down the line.
                if !extends.is_empty() {
                    format!(": {} + 'static", base_traits.join(" + "))
                } else {
                    ": 'static".to_string()
                }
            };

            mod_interior.push(BlankLine);
            mod_interior.push(Line(format!("pub struct Client{bracketed_params} {{")));
            mod_interior.push(indent(Line(fmt!(
                ctx,
                "pub client: {capnp}::capability::Client,"
            ))));
            if is_generic {
                mod_interior.push(indent(Line(params.phantom_data_type.clone())));
            }
            mod_interior.push(line("}"));
            mod_interior.push(
                Branch(vec![
                    Line(fmt!(ctx,"impl {bracketed_params} {capnp}::capability::FromClientHook for Client{bracketed_params} {{")),
                    indent(Line(fmt!(ctx,"fn new(hook: Box<{capnp}::capability::DynClientHook>) -> Self {{"))),
                    indent(indent(Line(fmt!(ctx,"Self {{ client: {capnp}::capability::Client::new(hook), {} }}", params.phantom_data_value)))),
                    indent(line("}")),
                    indent(Line(fmt!(ctx,"fn into_client_hook(self) -> Box<{capnp}::capability::DynClientHook> {{"))),
                    indent(indent(line("self.client.hook"))),
                    indent(line("}")),
                    indent(Line(fmt!(ctx,"fn as_client_hook(&self) -> &{capnp}::capability::DynClientHook {{"))),
                    indent(indent(line("&*self.client.hook"))),
                    indent(line("}")),
                    line("}")]));

            mod_interior.push(if !is_generic {
                Branch(vec![
                    Line("#[derive(Copy, Clone)]".into()),
                    line("pub struct Owned(());"),
                    Line(fmt!(ctx,"impl {capnp}::introspect::Introspect for Owned {{ fn introspect() -> {capnp}::introspect::Type {{ {capnp}::introspect::TypeVariant::Capability.into() }} }}")),
                    Line(fmt!(ctx,"impl {capnp}::traits::Owned for Owned {{ type Reader<'a> = Client; type Builder<'a> = Client; }}")),
                    Line(fmt!(ctx,"impl {capnp}::traits::Pipelined for Owned {{ type Pipeline = Client; }}"))])
            } else {
                Branch(vec![
                    Line("#[derive(Copy, Clone)]".into()),
                    Line(format!("pub struct Owned<{}> {} {{", params.params, params.where_clause)),
                    indent(Line(params.phantom_data_type.clone())),
                    line("}"),
                    Line(fmt!(ctx,
                              "impl <{0}> {capnp}::introspect::Introspect for Owned <{0}> {1} {{ fn introspect() -> {capnp}::introspect::Type {{ {capnp}::introspect::TypeVariant::Capability.into() }} }}",
                              params.params, params.where_clause)),
                    Line(fmt!(ctx,
                        "impl <{0}> {capnp}::traits::Owned for Owned <{0}> {1} {{ type Reader<'a> = Client<{0}>; type Builder<'a> = Client<{0}>; }}",
                        params.params, params.where_clause)),
                    Line(fmt!(ctx,
                        "impl <{0}> {capnp}::traits::Pipelined for Owned <{0}> {1} {{ type Pipeline = Client{2}; }}",
                        params.params, params.where_clause, bracketed_params))])
            });

            mod_interior.push(Branch(vec![
                Line(fmt!(ctx,"impl <'a,{0}> {capnp}::traits::FromPointerReader<'a> for Client<{0}> {1} {{",
                    params.params, params.where_clause)),
                indent(vec![
                        Line(fmt!(ctx,"fn get_from_pointer(reader: &{capnp}::private::layout::PointerReader<'a>, _default: ::core::option::Option<&'a [{capnp}::Word]>) -> {capnp}::Result<Self> {{")),
                        indent(Line(fmt!(ctx,"::core::result::Result::Ok({capnp}::capability::FromClientHook::new(reader.get_capability()?))"))),
                        line("}")]),
                line("}")]));

            mod_interior.push(Branch(vec![
                Line(fmt!(ctx,"impl <'a,{0}> {capnp}::traits::FromPointerBuilder<'a> for Client<{0}> {1} {{",
                             params.params, params.where_clause)),
                indent(vec![
                            Line(fmt!(ctx,"fn init_pointer(_builder: {capnp}::private::layout::PointerBuilder<'a>, _size: u32) -> Self {{")),
                            indent(line("unimplemented!()")),
                            line("}"),
                            Line(fmt!(ctx,"fn get_from_pointer(builder: {capnp}::private::layout::PointerBuilder<'a>, _default: ::core::option::Option<&'a [{capnp}::Word]>) -> {capnp}::Result<Self> {{")),
                            indent(Line(fmt!(ctx,"::core::result::Result::Ok({capnp}::capability::FromClientHook::new(builder.get_capability()?))"))),
                            line("}")]),
                line("}"),
                BlankLine]));

            mod_interior.push(Branch(vec![
                Line(fmt!(ctx,
                    "impl <{0}> {capnp}::traits::SetterInput<Owned<{0}>> for Client<{0}> {1} {{",
                    params.params, params.where_clause)),
                indent(vec![
                            Line(fmt!(ctx,"fn set_pointer_builder(mut pointer: {capnp}::private::layout::PointerBuilder<'_>, from: Self, _canonicalize: bool) -> {capnp}::Result<()> {{")),
                            indent(Line("pointer.set_capability(from.client.hook);".to_string())),
                            indent(Line("::core::result::Result::Ok(())".to_string())),
                            line("}")
                        ]
                ),
                line("}")]));

            mod_interior.push(Branch(vec![
                Line(fmt!(ctx,
                    "impl {bracketed_params} {capnp}::traits::HasTypeId for Client{bracketed_params} {{"
                )),
                indent(Line(
                    "const TYPE_ID: u64 = _private::TYPE_ID;".to_string(),
                )),
                line("}"),
            ]));

            mod_interior.push(Branch(vec![
                Line(format!(
                    "impl {bracketed_params} Clone for Client{bracketed_params} {{"
                )),
                indent(line("fn clone(&self) -> Self {")),
                indent(indent(Line(format!(
                    "Self {{ client: self.client.clone(), {} }}",
                    params.phantom_data_value
                )))),
                indent(line("}")),
                line("}"),
            ]));

            mod_interior.push(Branch(vec![
                Line(format!(
                    "impl {bracketed_params} Client{bracketed_params} {{"
                )),
                indent(client_impl_interior),
                line("}"),
            ]));

            mod_interior.push(Branch(vec![
                Line(format!(
                    "pub trait Server<{}> {} {} {{",
                    params.params, server_base, params.where_clause
                )),
                indent(server_interior),
                line("}"),
            ]));

            mod_interior.push(Branch(vec![
                Line(format!(
                    "pub struct ServerDispatch<_T,{}> {{",
                    params.params
                )),
                indent(line(fmt!(ctx, "pub server: {capnp}::capability::Rc<_T>,"))),
                indent(if is_generic {
                    vec![Line(params.phantom_data_type.clone())]
                } else {
                    vec![]
                }),
                line("}"),
            ]));

            mod_interior.push(Branch(vec![
                Line(
                    fmt!(ctx,"impl <_S: Server{1} + 'static, {0}> {capnp}::capability::FromServer<_S> for Client{1} {2}  {{",
                            params.params, bracketed_params, params.where_clause)),
                indent(vec![
                    Line(format!("type Dispatch = ServerDispatch<_S, {}>;", params.params)),
                    Line(fmt!(ctx, "fn from_server(s: {capnp}::capability::Rc<_S>) -> ServerDispatch<_S, {}> {{", params.params)),
                    indent(Line(format!("ServerDispatch {{ server: s, {} }}", params.phantom_data_value))),
                    line("}"),
                ]),
                line("}"),
            ]));

            mod_interior.push(
                Branch(vec![
                    (if is_generic {
                        Line(format!("impl <{}, _T: Server{}> ::core::ops::Deref for ServerDispatch<_T,{}> {} {{", params.params, bracketed_params, params.params, params.where_clause))
                    } else {
                        line("impl <_T: Server> ::core::ops::Deref for ServerDispatch<_T> {")
                    }),
                    indent(line("type Target = _T;")),
                    indent(line("fn deref(&self) -> &_T { &self.server}")),
                    line("}"),
                    ]));

            mod_interior.push(
                Branch(vec![
                    (if is_generic {
                        Line(format!("impl <{}, _T: Server{}> ::core::clone::Clone for ServerDispatch<_T,{}> {} {{", params.params, bracketed_params, params.params, params.where_clause))
                    } else {
                        line("impl <_T: Server> ::core::clone::Clone for ServerDispatch<_T> {")
                    }),
                    indent(line(
                        format!("fn clone(&self) -> Self {{ Self {{ server: self.server.clone(), {} }} }}", params.phantom_data_value))),
                    line("}"),
                    ]));

            mod_interior.push(
                Branch(vec![
                    (if is_generic {
                        Line(fmt!(ctx,"impl <{}, _T: Server{}> {capnp}::capability::Server for ServerDispatch<_T,{}> {} {{", params.params, bracketed_params, params.params, params.where_clause))
                    } else {
                        Line(fmt!(ctx,"impl <_T: Server> {capnp}::capability::Server for ServerDispatch<_T> {{"))
                    }),
                    indent(Line(fmt!(ctx,"fn dispatch_call(self, interface_id: u64, method_id: u16, params: {capnp}::capability::Params<{capnp}::any_pointer::Owned>, results: {capnp}::capability::Results<{capnp}::any_pointer::Owned>) -> {capnp}::capability::DispatchCallResult {{"))),
                    indent(indent(line("match interface_id {"))),
                    indent(indent(indent(line("_private::TYPE_ID => Self::dispatch_call_internal(self.server, method_id, params, results),")))),
                    indent(indent(indent(base_dispatch_arms))),
                    indent(indent(indent(Line(fmt!(ctx,"_ => {{ {capnp}::capability::DispatchCallResult::new({capnp}::capability::Promise::err({capnp}::Error::unimplemented(\"Method not implemented.\".to_string())), false) }}"))))),
                    indent(indent(line("}"))),
                    indent(line("}")),

                    indent(Line(fmt!(ctx, "fn as_ptr(&self) -> usize {{ {capnp}::capability::Rc::as_ptr(&self.server) as usize }}"))),

                    line("}")]));

            mod_interior.push(
                Branch(vec![
                    (if is_generic {
                        Line(format!("impl <{}, _T: Server{}> ServerDispatch<_T,{}> {} {{", params.params, bracketed_params, params.params, params.where_clause))
                    } else {
                        line("impl <_T :Server> ServerDispatch<_T> {")
                    }),

                    indent(Line(fmt!(ctx,"pub fn dispatch_call_internal(this: {capnp}::capability::Rc<_T>, method_id: u16, params: {capnp}::capability::Params<{capnp}::any_pointer::Owned>, results: {capnp}::capability::Results<{capnp}::any_pointer::Owned>) -> {capnp}::capability::DispatchCallResult {{"))),
                    indent(indent(line("match method_id {"))),
                    indent(indent(indent(dispatch_arms))),
                    indent(indent(indent(Line(fmt!(ctx,"_ => {{ {capnp}::capability::DispatchCallResult::new({capnp}::capability::Promise::err({capnp}::Error::unimplemented(\"Method not implemented.\".to_string())), false) }}"))))),
                    indent(indent(line("}"))),
                    indent(line("}")),
                    line("}")]));

            mod_interior.push(Branch(vec![
                line("pub(crate) mod _private {"),
                indent(private_mod_interior),
                line("}"),
            ]));

            mod_interior.push(Branch(vec![Branch(nested_output)]));

            output.push(BlankLine);
            if is_generic {
                output.push(Line(format!(
                    "pub mod {} {{ /* ({}) */",
                    node_name,
                    params.expanded_list.join(",")
                )));
            } else {
                output.push(Line(format!("pub mod {node_name} {{")));
            }
            output.push(indent(mod_interior));
            output.push(line("}"));
        }

        node::Const(c) => {
            let styled_name = ctx.get_last_name(node_id)?.to_ascii_uppercase();

            let typ = c.get_type()?;
            let formatted_text = match (typ.which()?, c.get_value()?.which()?) {
                (type_::Void(()), value::Void(())) => {
                    Line(format!("pub const {styled_name}: () = ();"))
                }
                (type_::Bool(()), value::Bool(b)) => {
                    Line(format!("pub const {styled_name}: bool = {b};"))
                }
                (type_::Int8(()), value::Int8(i)) => {
                    Line(format!("pub const {styled_name}: i8 = {i};"))
                }
                (type_::Int16(()), value::Int16(i)) => {
                    Line(format!("pub const {styled_name}: i16 = {i};"))
                }
                (type_::Int32(()), value::Int32(i)) => {
                    Line(format!("pub const {styled_name}: i32 = {i};"))
                }
                (type_::Int64(()), value::Int64(i)) => {
                    Line(format!("pub const {styled_name}: i64 = {i};"))
                }
                (type_::Uint8(()), value::Uint8(i)) => {
                    Line(format!("pub const {styled_name}: u8 = {i};"))
                }
                (type_::Uint16(()), value::Uint16(i)) => {
                    Line(format!("pub const {styled_name}: u16 = {i};"))
                }
                (type_::Uint32(()), value::Uint32(i)) => {
                    Line(format!("pub const {styled_name}: u32 = {i};"))
                }
                (type_::Uint64(()), value::Uint64(i)) => {
                    Line(format!("pub const {styled_name}: u64 = {i};"))
                }

                (type_::Float32(()), value::Float32(f)) => {
                    let literal = match f.classify() {
                        std::num::FpCategory::Nan => "f32::NAN".into(),
                        std::num::FpCategory::Infinite => {
                            if f.is_sign_positive() {
                                "f32::INFINITY".into()
                            } else {
                                "f32::NEG_INFINITY".into()
                            }
                        }
                        _ => format!("{f:e}"),
                    };
                    Line(format!("pub const {styled_name}: f32 = {literal};"))
                }

                (type_::Float64(()), value::Float64(f)) => {
                    let literal = match f.classify() {
                        std::num::FpCategory::Nan => "f64::NAN".into(),
                        std::num::FpCategory::Infinite => {
                            if f.is_sign_positive() {
                                "f64::INFINITY".into()
                            } else {
                                "f64::NEG_INFINITY".into()
                            }
                        }
                        _ => format!("{f:e}"),
                    };
                    Line(format!("pub const {styled_name}: f64 = {literal};"))
                }

                (type_::Enum(e), value::Enum(v)) => {
                    if let Some(node) = ctx.node_map.get(&e.get_type_id()) {
                        match node.which()? {
                            node::Enum(e) => {
                                let enumerants = e.get_enumerants()?;
                                if let Some(enumerant) = enumerants.try_get(u32::from(v)) {
                                    let variant =
                                        capitalize_first_letter(get_enumerant_name(enumerant)?);
                                    let type_string = typ.type_string(ctx, Leaf::Owned)?;
                                    Line(format!(
                                        "pub const {}: {} = {}::{};",
                                        styled_name, type_string, type_string, variant
                                    ))
                                } else {
                                    return Err(Error::failed(format!(
                                        "enumerant out of range: {v}"
                                    )));
                                }
                            }
                            _ => {
                                return Err(Error::failed(format!(
                                    "bad enum type ID: {}",
                                    e.get_type_id()
                                )));
                            }
                        }
                    } else {
                        return Err(Error::failed(format!(
                            "bad enum type ID: {}",
                            e.get_type_id()
                        )));
                    }
                }

                (type_::Text(()), value::Text(t)) => Line(format!(
                    "pub const {styled_name}: &str = {:?};",
                    t?.to_str()?
                )),
                (type_::Data(()), value::Data(d)) => {
                    Line(format!("pub const {styled_name}: &[u8] = &{:?};", d?))
                }

                (type_::List(_), value::List(v)) => {
                    generate_pointer_constant(ctx, &styled_name, typ, v)?
                }
                (type_::Struct(_), value::Struct(v)) => {
                    generate_pointer_constant(ctx, &styled_name, typ, v)?
                }

                (type_::Interface(_t), value::Interface(())) => {
                    return Err(Error::unimplemented("interface constants".to_string()));
                }
                (type_::AnyPointer(_), value::AnyPointer(_pr)) => {
                    return Err(Error::unimplemented("anypointer constants".to_string()));
                }

                _ => {
                    return Err(Error::failed("type does not match value".to_string()));
                }
            };

            output.push(formatted_text);
        }

        node::Annotation(annotation_reader) => {
            let is_generic = node_reader.get_is_generic();
            let params = node_reader.parameters_texts(ctx);
            let last_name = ctx.get_last_name(node_id)?;
            let mut interior = vec![];
            interior.push(Line(format!("pub const ID: u64 = 0x{node_id:x};")));

            let ty = annotation_reader.get_type()?;
            if !is_generic {
                interior.push(Line(fmt!(ctx,
                    "pub fn get_type() -> {capnp}::introspect::Type {{ <{} as {capnp}::introspect::Introspect>::introspect() }}", ty.type_string(ctx, Leaf::Owned)?)));
            } else {
                interior.push(Line(fmt!(ctx,"pub fn get_type<{0}>() -> {capnp}::introspect::Type {1} {{ <{2} as {capnp}::introspect::Introspect>::introspect() }}", params.params, params.where_clause, ty.type_string(ctx, Leaf::Owned)?)));
            }
            output.push(Branch(vec![
                Line(format!("pub mod {last_name} {{")),
                indent(interior),
                Line("}".into()),
            ]));
        }
    }

    Ok(Branch(output))
}

// TODO: make indent take Into<FormattedText>, impl Into<FormattedText> for vec (branch)