aion_package/codegen/

schema_emit.rs

//! Emission of the generated `schemas/*.json` artifacts.
//!
//! Types-first (ADR-014): `schemas/*.json` is a GENERATED artifact — emitted
//! from the boundary types the author declared in `src/<pkg>_io.gleam`, never
//! authored. The emitted documents keep serving their real consumers
//! untouched: packaging validation (`workflow.toml` `input_schema` /
//! `output_schema`), `aion input` skeletons, and external reference (agents,
//! HTTP clients, docs).
//!
//! One document is emitted per boundary type, at `schemas/<stem>.json`, with
//! references to sibling types inlined structurally (the front-end rejects
//! reference cycles, so inlining terminates). Every emitted document carries a
//! `$comment` marker naming its origin; the marker is how this module tells
//! its own artifacts from hand-authored strays:
//!
//! - a marked file no longer backed by a type is STALE: removed on a write
//!   run, a loud drift error under `--check`;
//! - an unmarked `*.json` is a STRAY (a pre-types-first authored schema or a
//!   hand-written file): always a loud error carrying the migration hint,
//!   because schema-first authoring is gone and two sources of truth is the
//!   exact disease ADR-014 kills.
//!
//! Rendering is by hand (never a `serde_json` map) so the bytes are fully
//! deterministic: same model in, byte-identical documents out.

use std::fmt::Write as _;
use std::io;
use std::path::{Path, PathBuf};

use super::error::CodegenError;
use super::model::{BoundaryType, EnumDef, GleamType, RecordDef, TypeDef};
use super::project::{CodegenMode, check_on_disk};

/// Directory (relative to the project root) the schema artifacts are emitted
/// into.
const SCHEMAS_DIR: &str = "schemas";

/// The marker prefix every emitted schema carries in its `$comment`. Detection
/// checks for this prefix, so the package-specific suffix can name the types
/// module.
const MARKER_PREFIX: &str = "Generated by aion generate from src/";

/// The result of emitting (or checking) the schema artifacts.
#[derive(Debug)]
pub struct SchemaEmitReport {
    /// Every emitted schema path, relative to the project root, in type-name
    /// order.
    pub emitted: Vec<String>,
    /// Stale generated schemas removed by a write run (empty under `--check`).
    pub removed: Vec<String>,
    /// Whether the artifacts were written (`false` in check mode).
    pub written: bool,
}

/// Emits (or, in [`CodegenMode::Check`], verifies) `schemas/<stem>.json` for
/// every boundary type.
///
/// # Errors
///
/// Returns a [`CodegenError`] for a write/read failure, a stray unmarked
/// `*.json` in `schemas/`, and — in check mode — a missing, drifted, or stale
/// document.
pub fn emit_schemas(
    root: &Path,
    package_name: &str,
    types: &[BoundaryType],
    mode: CodegenMode,
) -> Result<SchemaEmitReport, CodegenError> {
    let schemas_dir = root.join(SCHEMAS_DIR);
    let mut emitted = Vec::with_capacity(types.len());
    let mut rendered: Vec<(PathBuf, String)> = Vec::with_capacity(types.len());
    for boundary in types {
        let contents = render_schema(package_name, boundary);
        emitted.push(boundary.file.display().to_string());
        rendered.push((root.join(&boundary.file), contents));
    }

    let written = match mode {
        CodegenMode::Write => {
            std::fs::create_dir_all(&schemas_dir).map_err(|source| CodegenError::Write {
                path: schemas_dir.clone(),
                source,
            })?;
            for (path, contents) in &rendered {
                std::fs::write(path, contents).map_err(|source| CodegenError::Write {
                    path: path.clone(),
                    source,
                })?;
            }
            true
        }
        CodegenMode::Check => {
            for (path, contents) in &rendered {
                check_on_disk(path, contents)?;
            }
            false
        }
    };

    let removed = reconcile_directory(&schemas_dir, &emitted, mode)?;
    Ok(SchemaEmitReport {
        emitted,
        removed,
        written,
    })
}

/// Walks `schemas/*.json` after emission and classifies every file that is not
/// an emitted artifact: marked files are stale generated output (removed on
/// write, a drift error under check); unmarked files are strays and always a
/// loud error with the migration hint.
fn reconcile_directory(
    schemas_dir: &Path,
    emitted: &[String],
    mode: CodegenMode,
) -> Result<Vec<String>, CodegenError> {
    let entries = match std::fs::read_dir(schemas_dir) {
        Ok(entries) => entries,
        // Check mode on a project that never emitted: the per-file
        // `check_on_disk` above already reported the missing artifacts.
        Err(source) if source.kind() == io::ErrorKind::NotFound => return Ok(Vec::new()),
        Err(source) => {
            return Err(CodegenError::SchemasDirRead {
                path: schemas_dir.to_path_buf(),
                source,
            });
        }
    };
    let mut removed = Vec::new();
    let mut names: Vec<PathBuf> = Vec::new();
    for entry in entries {
        let entry = entry.map_err(|source| CodegenError::SchemasDirRead {
            path: schemas_dir.to_path_buf(),
            source,
        })?;
        let path = entry.path();
        if path.is_file() && path.extension().is_some_and(|ext| ext == "json") {
            names.push(path);
        }
    }
    names.sort();

    for path in names {
        let file_name = path
            .file_name()
            .map(|name| name.to_string_lossy().into_owned())
            .unwrap_or_default();
        let relative = format!("{SCHEMAS_DIR}/{file_name}");
        if emitted.contains(&relative) {
            continue;
        }
        let contents =
            std::fs::read_to_string(&path).map_err(|source| CodegenError::CheckRead {
                path: path.clone(),
                source,
            })?;
        if !contents.contains(MARKER_PREFIX) {
            return Err(CodegenError::SchemaStray { path });
        }
        match mode {
            CodegenMode::Write => {
                std::fs::remove_file(&path).map_err(|source| CodegenError::Write {
                    path: path.clone(),
                    source,
                })?;
                removed.push(relative);
            }
            CodegenMode::Check => {
                return Err(CodegenError::CheckDrift { path });
            }
        }
    }
    Ok(removed)
}

/// Renders one boundary type's schema document, byte-deterministically.
fn render_schema(package_name: &str, boundary: &BoundaryType) -> String {
    let mut out = String::new();
    out.push_str("{\n");
    let _ = writeln!(
        out,
        "  \"$comment\": \"{MARKER_PREFIX}{package_name}_io.gleam — do not edit; run `aion generate`.\","
    );
    match boundary.defs.first() {
        Some(TypeDef::Record(record)) => render_record_body(&mut out, record, &boundary.defs, 1),
        Some(TypeDef::Enum(definition)) => render_enum_body(&mut out, definition, 1),
        None => {}
    }
    out.push_str("}\n");
    out
}

/// Renders a record's `type`/`required`/`additionalProperties`/`properties`
/// members at `indent` levels (the surrounding braces are the caller's).
fn render_record_body(out: &mut String, record: &RecordDef, defs: &[TypeDef], indent: usize) {
    let pad = "  ".repeat(indent);
    let _ = writeln!(out, "{pad}\"type\": \"object\",");
    let required: Vec<String> = record
        .fields
        .iter()
        .filter(|field| field.required)
        .map(|field| format!("\"{}\"", field.wire))
        .collect();
    let _ = writeln!(out, "{pad}\"required\": [{}],", required.join(", "));
    let _ = writeln!(out, "{pad}\"additionalProperties\": false,");
    if record.fields.is_empty() {
        let _ = writeln!(out, "{pad}\"properties\": {{}}");
        return;
    }
    let _ = writeln!(out, "{pad}\"properties\": {{");
    for (position, field) in record.fields.iter().enumerate() {
        let comma = if position + 1 == record.fields.len() {
            ""
        } else {
            ","
        };
        let value = render_type(&field.ty, defs, indent + 1);
        let _ = writeln!(out, "{pad}  \"{}\": {value}{comma}", field.wire);
    }
    let _ = writeln!(out, "{pad}}}");
}

/// Renders an enum's `type`/`enum` members at `indent` levels.
fn render_enum_body(out: &mut String, definition: &EnumDef, indent: usize) {
    let pad = "  ".repeat(indent);
    let _ = writeln!(out, "{pad}\"type\": \"string\",");
    let _ = writeln!(out, "{pad}\"enum\": [{}]", enum_values(definition));
}

/// The comma-joined quoted wire values of an enum.
fn enum_values(definition: &EnumDef) -> String {
    definition
        .variants
        .iter()
        .map(|variant| format!("\"{}\"", variant.wire))
        .collect::<Vec<_>>()
        .join(", ")
}

/// Renders a field type's schema value. Scalars, enums, and lists of them stay
/// on one line; object schemas (sibling record references) expand over
/// multiple lines with their continuation at `indent` levels.
fn render_type(ty: &GleamType, defs: &[TypeDef], indent: usize) -> String {
    match ty {
        GleamType::String => "{ \"type\": \"string\" }".to_owned(),
        GleamType::Int => "{ \"type\": \"integer\" }".to_owned(),
        GleamType::Float => "{ \"type\": \"number\" }".to_owned(),
        GleamType::Bool => "{ \"type\": \"boolean\" }".to_owned(),
        GleamType::List(inner) => format!(
            "{{ \"type\": \"array\", \"items\": {} }}",
            render_type(inner, defs, indent)
        ),
        GleamType::Named { type_name, .. } => {
            match defs.iter().find(|def| def.type_name() == type_name) {
                Some(TypeDef::Enum(definition)) => format!(
                    "{{ \"type\": \"string\", \"enum\": [{}] }}",
                    enum_values(definition)
                ),
                Some(TypeDef::Record(record)) => {
                    let pad = "  ".repeat(indent);
                    let mut nested = String::from("{\n");
                    render_record_body(&mut nested, record, defs, indent + 1);
                    let _ = write!(nested, "{pad}}}");
                    nested
                }
                // The front-end guarantees every named reference resolves in
                // the closure; an unresolvable one would already have failed
                // there, so render nothing rather than panic.
                None => "{ }".to_owned(),
            }
        }
    }
}

#[cfg(test)]
mod tests {
    use std::path::PathBuf;

    use super::{emit_schemas, render_schema};
    use crate::codegen::error::CodegenError;
    use crate::codegen::model::{
        BoundaryType, EnumDef, EnumVariant, Field, GleamType, RecordDef, TypeDef,
    };
    use crate::codegen::project::CodegenMode;
    use crate::project::fixture;

    type TestResult = Result<(), Box<dyn std::error::Error>>;

    fn named(type_name: &str) -> GleamType {
        GleamType::Named {
            type_name: type_name.to_owned(),
            fn_prefix: crate::codegen::names::pascal_to_snake(type_name),
        }
    }

    fn field(wire: &str, ty: GleamType, required: bool) -> Field {
        Field {
            wire: wire.to_owned(),
            ty,
            required,
        }
    }

    fn record_def(type_name: &str, fields: Vec<Field>) -> TypeDef {
        TypeDef::Record(RecordDef {
            type_name: type_name.to_owned(),
            fn_prefix: crate::codegen::names::pascal_to_snake(type_name),
            fields,
        })
    }

    fn boundary(type_name: &str, defs: Vec<TypeDef>) -> BoundaryType {
        let stem = crate::codegen::names::pascal_to_snake(type_name);
        BoundaryType {
            file: PathBuf::from(format!("schemas/{stem}.json")),
            stem,
            root: named(type_name),
            defs,
        }
    }

    fn kind_enum() -> TypeDef {
        TypeDef::Enum(EnumDef {
            type_name: "OrderKind".to_owned(),
            fn_prefix: "order_kind".to_owned(),
            variants: vec![
                EnumVariant {
                    constructor: "OrderKindStandard".to_owned(),
                    wire: "standard".to_owned(),
                },
                EnumVariant {
                    constructor: "OrderKindRush".to_owned(),
                    wire: "rush".to_owned(),
                },
            ],
        })
    }

    #[test]
    fn record_schema_renders_required_optional_list_enum_and_nested() {
        let order = boundary(
            "OrderInput",
            vec![
                record_def(
                    "OrderInput",
                    vec![
                        field("order_id", GleamType::String, true),
                        field("quantity", GleamType::Int, true),
                        field("ratio", GleamType::Float, true),
                        field("rush", GleamType::Bool, true),
                        field("tags", GleamType::List(Box::new(GleamType::String)), true),
                        field("kind", named("OrderKind"), true),
                        field("line", named("OrderLine"), true),
                        field("note", GleamType::String, false),
                    ],
                ),
                kind_enum(),
                record_def("OrderLine", vec![field("sku", GleamType::String, true)]),
            ],
        );

        let expected = r#"{
  "$comment": "Generated by aion generate from src/demo_io.gleam — do not edit; run `aion generate`.",
  "type": "object",
  "required": ["order_id", "quantity", "ratio", "rush", "tags", "kind", "line"],
  "additionalProperties": false,
  "properties": {
    "order_id": { "type": "string" },
    "quantity": { "type": "integer" },
    "ratio": { "type": "number" },
    "rush": { "type": "boolean" },
    "tags": { "type": "array", "items": { "type": "string" } },
    "kind": { "type": "string", "enum": ["standard", "rush"] },
    "line": {
      "type": "object",
      "required": ["sku"],
      "additionalProperties": false,
      "properties": {
        "sku": { "type": "string" }
      }
    },
    "note": { "type": "string" }
  }
}
"#;
        assert_eq!(render_schema("demo", &order), expected);
    }

    #[test]
    fn enum_schema_and_empty_record_render() {
        let kind = boundary("OrderKind", vec![kind_enum()]);
        assert_eq!(
            render_schema("demo", &kind),
            "{\n  \"$comment\": \"Generated by aion generate from src/demo_io.gleam — do not \
             edit; run `aion generate`.\",\n  \"type\": \"string\",\n  \"enum\": [\"standard\", \
             \"rush\"]\n}\n"
        );

        let blank = boundary("Blank", vec![record_def("Blank", Vec::new())]);
        let rendered = render_schema("demo", &blank);
        assert!(rendered.contains("\"required\": [],"));
        assert!(rendered.contains("\"properties\": {}"));
    }

    #[test]
    fn emitted_schemas_parse_as_json_and_are_deterministic() -> TestResult {
        let order = boundary(
            "OrderInput",
            vec![record_def(
                "OrderInput",
                vec![
                    field("order_id", GleamType::String, true),
                    field("note", GleamType::String, false),
                ],
            )],
        );
        let first = render_schema("demo", &order);
        let second = render_schema("demo", &order);
        assert_eq!(first, second, "rendering must be deterministic");
        let parsed: serde_json::Value = serde_json::from_str(&first)?;
        assert_eq!(parsed["type"], "object");
        assert_eq!(parsed["required"], serde_json::json!(["order_id"]));
        assert_eq!(parsed["additionalProperties"], false);
        assert_eq!(parsed["properties"]["note"]["type"], "string");
        Ok(())
    }

    #[test]
    fn write_then_check_round_trips_and_check_catches_a_hand_edit() -> TestResult {
        let root = fixture::temp_project("schema-emit-roundtrip", &[])?;
        let types = [boundary(
            "OrderInput",
            vec![record_def(
                "OrderInput",
                vec![field("order_id", GleamType::String, true)],
            )],
        )];

        let report = emit_schemas(&root, "demo", &types, CodegenMode::Write)?;
        assert!(report.written);
        assert_eq!(report.emitted, vec!["schemas/order_input.json".to_owned()]);
        assert!(root.join("schemas/order_input.json").is_file());

        let checked = emit_schemas(&root, "demo", &types, CodegenMode::Check)?;
        assert!(!checked.written);

        let path = root.join("schemas/order_input.json");
        let mut tampered = std::fs::read_to_string(&path)?;
        tampered.push('\n');
        std::fs::write(&path, &tampered)?;
        let result = emit_schemas(&root, "demo", &types, CodegenMode::Check);
        let Err(CodegenError::CheckDrift { path: drifted }) = result else {
            std::fs::remove_dir_all(&root)?;
            return Err(format!("expected CheckDrift, got {result:?}").into());
        };
        assert_eq!(drifted, path);
        std::fs::remove_dir_all(&root)?;
        Ok(())
    }

    #[test]
    fn stray_unmarked_json_is_a_loud_error_with_the_migration_hint() -> TestResult {
        let root = fixture::temp_project(
            "schema-emit-stray",
            &[("schemas/legacy.json", b"{ \"type\": \"object\" }" as &[u8])],
        )?;
        let types = [boundary(
            "OrderInput",
            vec![record_def(
                "OrderInput",
                vec![field("order_id", GleamType::String, true)],
            )],
        )];

        let result = emit_schemas(&root, "demo", &types, CodegenMode::Write);
        let Err(CodegenError::SchemaStray { path }) = result else {
            std::fs::remove_dir_all(&root)?;
            return Err(format!("expected SchemaStray, got {result:?}").into());
        };
        assert_eq!(path, root.join("schemas/legacy.json"));
        let message = CodegenError::SchemaStray { path }.to_string();
        assert!(
            message.contains("src/<package>_io.gleam") && message.contains("aion generate"),
            "the stray error must carry the migration hint: {message}"
        );
        std::fs::remove_dir_all(&root)?;
        Ok(())
    }

    #[test]
    fn stale_marked_schema_is_removed_on_write_and_drift_under_check() -> TestResult {
        let root = fixture::temp_project("schema-emit-stale", &[])?;
        let both = [
            boundary("NewType", vec![record_def("NewType", Vec::new())]),
            boundary("OldType", vec![record_def("OldType", Vec::new())]),
        ];
        emit_schemas(&root, "demo", &both, CodegenMode::Write)?;
        assert!(root.join("schemas/old_type.json").is_file());

        // The model moves on: OldType is renamed away, so its emitted schema
        // is now a stale generated artifact.
        let new = [boundary("NewType", vec![record_def("NewType", Vec::new())])];
        // Under --check the stale marked file is drift.
        let result = emit_schemas(&root, "demo", &new, CodegenMode::Check);
        assert!(
            matches!(result, Err(CodegenError::CheckDrift { ref path }) if path.ends_with("old_type.json")),
            "stale marked schema must be drift under check: {result:?}"
        );
        // A write run removes it.
        let report = emit_schemas(&root, "demo", &new, CodegenMode::Write)?;
        assert_eq!(report.removed, vec!["schemas/old_type.json".to_owned()]);
        assert!(!root.join("schemas/old_type.json").exists());
        assert!(root.join("schemas/new_type.json").is_file());
        std::fs::remove_dir_all(&root)?;
        Ok(())
    }
}