t_backend_c/

lib.rs

#![deny(missing_docs)]

//! C code generator for the T programming language.
//!
//! Transforms a typed AST (`Module`) into C99/C11 source code.

use std::collections::{HashMap, HashSet};
use std::fmt::Write;

use t_ree::{
    declaration::{Declaration, FunctionDefinition, Module, Newtype, Parameter, ParameterList},
    expression::{Binding, Block, Expression, ExpressionKind, Statement},
    types::{FloatWidth, IntWidth, Mutability, Signedness, Type},
};

fn element_byte_size(element: &Type) -> usize {
    match element {
        Type::Int(width, _) => width.byte_size(),
        Type::Float(width) => width.byte_size(),
        Type::Bool => 1,
        Type::Pointer(..) => 8,
        _ => 4,
    }
}

/// Compiles a T module into C source code.
pub fn compile(module: &Module) -> String {
    let mut emitter = Emitter::new();
    emitter.emit_module(module);
    emitter.output
}

struct Emitter {
    output: String,
    indent_level: usize,
    labels: HashMap<String, Vec<Parameter>>,
    newtypes: HashMap<String, Type>,
    auto_ref_variables: HashSet<String>,
    pointer_param_variables: HashSet<String>,
    label_param_names: HashMap<String, String>,
    in_main: bool,
    temp_counter: usize,
    function_defers: Vec<Statement>,
    shadow_scopes: Vec<HashMap<String, String>>,
    shadow_counter: usize,
    has_stdio: bool,
}

impl Emitter {
    fn new() -> Self {
        Self {
            output: String::new(),
            indent_level: 0,
            labels: HashMap::new(),
            newtypes: HashMap::new(),
            auto_ref_variables: HashSet::new(),
            pointer_param_variables: HashSet::new(),
            label_param_names: HashMap::new(),
            function_defers: Vec::new(),
            in_main: false,
            temp_counter: 0,
            shadow_scopes: Vec::new(),
            shadow_counter: 0,
            has_stdio: false,
        }
    }

    fn push(&mut self, text: &str) {
        self.output.push_str(text);
    }

    fn newline(&mut self) {
        self.output.push('\n');
    }

    fn indent(&mut self) {
        for _ in 0..self.indent_level {
            self.push("    ");
        }
    }

    fn emit_module(&mut self, module: &Module) {
        self.push("#include <stdint.h>\n");
        self.push("#include <stdbool.h>\n");
        self.push("#include <stddef.h>\n");
        self.has_stdio = self.uses_print(module)
            || module.iter().any(|d| {
                matches!(d, Declaration::Import(path) if path == "stdio.h" || path.ends_with("/stdio.h"))
            });
        if self.has_stdio {
            self.push("#include <stdio.h>\n");
        }
        self.newline();

        for declaration in module {
            if let Declaration::Type(newtype) = declaration {
                self.newtypes
                    .insert(newtype.name.clone(), newtype.inner_type.clone());
                if matches!(&newtype.inner_type, Type::Tuple(fields) if !fields.is_empty())
                    || matches!(&newtype.inner_type, Type::Enum(_))
                {
                    writeln!(self.output, "struct {};", newtype.name).unwrap();
                }
            }
        }
        self.newline();

        for declaration in module {
            self.emit_declaration(declaration);
            self.newline();
        }
    }

    fn uses_print(&self, module: &Module) -> bool {
        module.iter().any(|decl| {
            if let Declaration::Function(func) = decl {
                self.block_uses_print(&func.body)
            } else {
                false
            }
        })
    }

    fn block_uses_print(&self, block: &Block) -> bool {
        block
            .statements
            .iter()
            .any(|s| self.statement_uses_print(s))
            || block
                .result
                .as_ref()
                .is_some_and(|e| self.expression_uses_print(e))
    }

    fn statement_uses_print(&self, statement: &Statement) -> bool {
        match statement {
            Statement::Expression(e) | Statement::Return(Some(e)) => self.expression_uses_print(e),
            Statement::Let { value, .. } => self.expression_uses_print(value),
            Statement::Assign(target, value) => {
                self.expression_uses_print(target) || self.expression_uses_print(value)
            }
            Statement::Label {
                initial_arguments, ..
            } => initial_arguments
                .iter()
                .any(|e| self.expression_uses_print(e)),
            Statement::Jump { arguments, .. } => {
                arguments.iter().any(|e| self.expression_uses_print(e))
            }
            Statement::Return(None) | Statement::MultiReplace { .. } => false,
            Statement::Defer(inner) => self.statement_uses_print(inner),
        }
    }

    fn expression_uses_print(&self, expression: &Expression) -> bool {
        match &expression.kind {
            ExpressionKind::Print(_) => true,
            ExpressionKind::Block(block) => self.block_uses_print(block),
            ExpressionKind::If {
                condition,
                then_branch,
                else_branch,
            } => {
                self.expression_uses_print(condition)
                    || self.block_uses_print(then_branch)
                    || else_branch
                        .as_ref()
                        .is_some_and(|b| self.block_uses_print(b))
            }
            ExpressionKind::Match { value, arms } => {
                self.expression_uses_print(value)
                    || arms.iter().any(|arm| self.block_uses_print(&arm.body))
            }
            ExpressionKind::Call(callee, args) => {
                self.expression_uses_print(callee)
                    || args.iter().any(|e| self.expression_uses_print(e))
            }
            ExpressionKind::BinaryOperation(_, left, right) => {
                self.expression_uses_print(left) || self.expression_uses_print(right)
            }
            ExpressionKind::UnaryOperation(_, operand)
            | ExpressionKind::Dereference(operand)
            | ExpressionKind::Convert(operand, _)
            | ExpressionKind::Transmute(operand, _) => self.expression_uses_print(operand),
            ExpressionKind::Replace(target, value) => {
                self.expression_uses_print(target) || self.expression_uses_print(value)
            }
            _ => false,
        }
    }

    fn emit_type(&mut self, ty: &Type) {
        match ty {
            Type::Never => self.push("void"),
            Type::Bool => self.push("bool"),
            Type::Int(IntWidth::WSize, Signedness::Unsigned) => self.push("size_t"),
            Type::Int(IntWidth::WSize, Signedness::Signed) => self.push("ptrdiff_t"),
            Type::Int(width, signedness) => {
                if matches!(signedness, Signedness::Unsigned) {
                    self.push("u");
                }
                write!(self.output, "int{}_t", width.bit_size()).unwrap();
            }
            Type::Float(FloatWidth::W32) => self.push("float"),
            Type::Float(FloatWidth::W64) => self.push("double"),
            Type::Pointer(mutability, inner) => {
                if matches!(mutability, Mutability::Shared) {
                    self.push("const ");
                }
                self.emit_type(inner);
                self.push(" *");
            }
            Type::Array(element, size) => {
                self.emit_type(element);
                write!(self.output, "[{size}]").unwrap();
            }
            Type::Vector(element, lanes) => {
                let byte_size = lanes * element_byte_size(element);
                self.emit_type(element);
                write!(self.output, " __attribute__((vector_size({byte_size})))").unwrap();
            }
            Type::Slice(mutability, inner) => {
                self.push("struct { ");
                if matches!(mutability, Mutability::Shared) {
                    self.push("const ");
                }
                self.emit_type(inner);
                self.push(" *data; size_t length; }");
            }
            Type::Tuple(fields) if fields.is_empty() => self.push("void"),
            Type::Tuple(fields) => {
                self.push("struct { ");
                for (index, field) in fields.iter().enumerate() {
                    self.emit_type(field);
                    write!(self.output, " _{index}; ").unwrap();
                }
                self.push("}");
            }
            Type::Enum(variants) => {
                self.push("struct { uint8_t tag; union { ");
                for variant in variants {
                    self.emit_type(variant);
                    if let Type::Named(name) = variant {
                        write!(self.output, " {name}; ").unwrap();
                    }
                }
                self.push("} value; }");
            }
            Type::Named(name) => {
                let needs_struct = self.newtypes.get(name).is_some_and(|inner| {
                    matches!(inner, Type::Tuple(fields) if !fields.is_empty())
                        || matches!(inner, Type::Enum(_))
                        || matches!(inner, Type::Array(..))
                });
                if needs_struct {
                    self.push("struct ");
                }
                self.push(name);
            }
            Type::Function(signature) => {
                self.emit_type(&signature.return_type);
                self.push(" (*)(");
                for (index, param) in signature.parameters.iter().enumerate() {
                    if index > 0 {
                        self.push(", ");
                    }
                    self.emit_type(param);
                }
                self.push(")");
            }
        }
    }

    fn emit_typed_name(&mut self, ty: &Type, name: &str) {
        match ty {
            Type::Array(element, size) => {
                self.emit_type(element);
                write!(self.output, " {name}[{size}]").unwrap();
            }
            Type::Function(signature) => {
                self.emit_type(&signature.return_type);
                write!(self.output, " (*{name})(").unwrap();
                for (index, param) in signature.parameters.iter().enumerate() {
                    if index > 0 {
                        self.push(", ");
                    }
                    self.emit_type(param);
                }
                self.push(")");
            }
            _ => {
                self.emit_type(ty);
                write!(self.output, " {name}").unwrap();
            }
        }
    }

    fn emit_parameter_list(&mut self, params: &ParameterList) {
        self.push("(");
        let parameters = params.parameters();
        if parameters.is_empty() {
            self.push("void");
        } else {
            self.emit_parameters(parameters);
            if matches!(params, ParameterList::Variadic(_)) {
                self.push(", ...");
            }
        }
        self.push(")");
    }

    fn emit_parameters(&mut self, parameters: &[Parameter]) {
        for (index, param) in parameters.iter().enumerate() {
            if index > 0 {
                self.push(", ");
            }
            if let Some(ty) = &param.parameter_type {
                let c_name = if self.newtypes.contains_key(&param.name)
                    && *ty != Type::Named(param.name.clone())
                {
                    format!("_{}", param.name)
                } else {
                    param.name.clone()
                };
                if c_name != param.name
                    && let Some(scope) = self.shadow_scopes.last_mut()
                {
                    scope.insert(param.name.clone(), c_name.clone());
                }
                self.emit_typed_name(ty, &c_name);
                if matches!(ty, Type::Pointer(..))
                    || self
                        .newtypes
                        .get(&param.name)
                        .is_some_and(|inner| matches!(inner, Type::Pointer(..)))
                {
                    self.auto_ref_variables.insert(c_name.clone());
                    self.pointer_param_variables.insert(c_name);
                }
            }
        }
    }

    fn emit_declaration(&mut self, declaration: &Declaration) {
        match declaration {
            Declaration::Type(newtype) => {
                self.newtypes
                    .insert(newtype.name.clone(), newtype.inner_type.clone());
                self.emit_newtype(newtype);
            }
            Declaration::Function(function) => self.emit_function(function, function.public),
            Declaration::Extern(extern_function) => {
                if !(self.has_stdio && Self::is_stdio_function(&extern_function.name)) {
                    self.emit_type(&extern_function.return_type);
                    write!(self.output, " {}", extern_function.name).unwrap();
                    self.emit_parameter_list(&extern_function.parameters);
                    self.push(";\n");
                }
            }
            Declaration::Constant(constant) => {
                if !constant.public {
                    self.push("static ");
                }
                self.push("const ");
                self.emit_typed_name(&constant.constant_type, &constant.name);
                self.push(" = ");
                self.emit_expression(&constant.value);
                self.push(";\n");
            }
            Declaration::Import(path) => {
                if !(self.has_stdio && (path == "stdio.h" || path.ends_with("/stdio.h"))) {
                    writeln!(self.output, "#include \"{path}\"").unwrap();
                }
            }
        }
    }

    fn emit_newtype(&mut self, newtype: &Newtype) {
        match &newtype.inner_type {
            Type::Tuple(fields) if !fields.is_empty() => {
                writeln!(self.output, "struct {} {{", newtype.name).unwrap();
                self.indent_level += 1;
                for field_type in fields {
                    self.indent();
                    let field_name = if let Type::Named(name) = field_type {
                        name.clone()
                    } else {
                        format!("_{}", self.output.len())
                    };
                    self.emit_typed_name(field_type, &field_name);
                    self.push(";\n");
                }
                self.indent_level -= 1;
                self.push("};\n");
            }
            Type::Enum(variants) => {
                writeln!(self.output, "struct {} {{", newtype.name).unwrap();
                self.indent_level += 1;
                self.indent();
                self.push("uint8_t tag;\n");
                self.indent();
                self.push("union {\n");
                self.indent_level += 1;
                for variant in variants {
                    self.indent();
                    let variant_name = if let Type::Named(name) = variant {
                        name.clone()
                    } else {
                        format!("_{}", self.output.len())
                    };
                    self.emit_typed_name(variant, &variant_name);
                    self.push(";\n");
                }
                self.indent_level -= 1;
                self.indent();
                self.push("} value;\n");
                self.indent_level -= 1;
                self.push("};\n");
            }
            Type::Array(element, size) => {
                writeln!(self.output, "struct {} {{", newtype.name).unwrap();
                self.indent_level += 1;
                self.indent();
                self.emit_type(element);
                writeln!(self.output, " data[{size}];").unwrap();
                self.indent_level -= 1;
                self.push("};\n");
            }
            _ => {
                self.push("typedef ");
                self.emit_typed_name(&newtype.inner_type, &newtype.name);
                self.push(";\n");
            }
        }
    }

    fn emit_label_declarations(&mut self) {
        for (label_name, params) in &self.labels.clone() {
            for param in params {
                if let Some(ty) = &param.parameter_type {
                    let qualified = format!("{label_name}_{}", param.name);
                    self.indent();
                    self.emit_typed_name(ty, &qualified);
                    self.push(";\n");
                }
            }
        }
    }

    fn register_label(&mut self, name: &str, parameters: &[Parameter]) {
        self.labels.insert(name.to_string(), parameters.to_vec());
        for param in parameters {
            self.label_param_names
                .insert(param.name.clone(), format!("{name}_{}", param.name));
        }
    }

    fn collect_labels(&mut self, block: &Block) {
        for statement in &block.statements {
            self.collect_labels_statement(statement);
        }
        if let Some(result) = &block.result {
            self.collect_labels_expression(result);
        }
    }

    fn collect_labels_statement(&mut self, statement: &Statement) {
        match statement {
            Statement::Label {
                name, parameters, ..
            } => self.register_label(name, parameters),
            Statement::Expression(expression) => self.collect_labels_expression(expression),
            Statement::Defer(inner) => self.collect_labels_statement(inner),
            _ => {}
        }
    }

    fn collect_labels_expression(&mut self, expression: &Expression) {
        match &expression.kind {
            ExpressionKind::Block(block) => self.collect_labels(block),
            ExpressionKind::If {
                then_branch,
                else_branch,
                ..
            } => {
                self.collect_labels(then_branch);
                if let Some(else_block) = else_branch {
                    self.collect_labels(else_block);
                }
            }
            ExpressionKind::Match { arms, .. } => {
                for arm in arms {
                    self.collect_labels(&arm.body);
                }
            }
            _ => {}
        }
    }

    fn push_shadow_scope(&mut self) {
        self.shadow_scopes.push(HashMap::new());
    }

    fn pop_shadow_scope(&mut self) {
        self.shadow_scopes.pop();
    }

    fn register_shadow(&mut self, name: &str) -> String {
        let already_declared = self
            .shadow_scopes
            .iter()
            .any(|scope| scope.contains_key(name));
        let emit_name = if already_declared {
            self.shadow_counter += 1;
            format!("{name}${}", self.shadow_counter)
        } else {
            name.into()
        };
        if let Some(scope) = self.shadow_scopes.last_mut() {
            scope.insert(name.into(), emit_name.clone());
        }
        emit_name
    }

    fn resolve_shadow<'a>(&'a self, name: &'a str) -> &'a str {
        for scope in self.shadow_scopes.iter().rev() {
            if let Some(resolved) = scope.get(name) {
                return resolved;
            }
        }
        name
    }

    fn emit_function(&mut self, function: &FunctionDefinition, public: bool) {
        self.labels.clear();
        self.auto_ref_variables.clear();
        self.pointer_param_variables.clear();
        self.label_param_names.clear();
        self.shadow_scopes.clear();
        self.shadow_counter = 0;
        self.push_shadow_scope();
        self.collect_labels(&function.body);
        let is_main = function.name == "main";
        let is_void = function.return_type == Type::Tuple(Vec::new());
        if !is_main && !public {
            self.push("static ");
        }
        if is_main {
            self.push("int32_t");
        } else {
            self.emit_type(&function.return_type);
        }
        write!(self.output, " {}(", function.name).unwrap();
        if function.parameters.is_empty() {
            self.push("void");
        } else {
            self.emit_parameters(&function.parameters);
        }
        self.push(") {\n");
        self.indent_level += 1;
        self.in_main = is_main;
        self.emit_label_declarations();
        let has_result = function.body.result.is_some();
        if is_void || (is_main && !has_result) {
            self.emit_function_body_void(&function.body);
        } else {
            self.emit_function_body(&function.body);
        }
        let ends_with_return = function
            .body
            .statements
            .last()
            .is_some_and(|s| matches!(s, Statement::Return(_)));
        if is_main && (is_void || !has_result) && !ends_with_return {
            self.indent();
            self.push("return 0;\n");
        }
        self.in_main = false;
        self.indent_level -= 1;
        self.push("}\n");
    }

    fn emit_function_body(&mut self, block: &Block) {
        self.function_defers = Self::collect_defers(&block.statements)
            .into_iter()
            .cloned()
            .collect();
        for statement in &block.statements {
            self.emit_statement(statement);
        }
        let defers = std::mem::take(&mut self.function_defers);
        for defer in defers.iter().rev() {
            self.emit_statement(defer);
        }
        if let Some(result) = &block.result {
            self.indent();
            self.push("return ");
            self.emit_expression(result);
            self.push(";\n");
        }
        self.function_defers.clear();
    }

    fn emit_function_body_void(&mut self, block: &Block) {
        self.function_defers = Self::collect_defers(&block.statements)
            .into_iter()
            .cloned()
            .collect();
        for statement in &block.statements {
            self.emit_statement(statement);
        }
        if let Some(result) = &block.result {
            self.indent();
            self.emit_expression(result);
            self.push(";\n");
        }
        let defers = std::mem::take(&mut self.function_defers);
        for defer in defers.iter().rev() {
            self.emit_statement(defer);
        }
    }

    fn emit_block_content(&mut self, block: &Block) {
        let defers = Self::collect_defers(&block.statements);
        for statement in &block.statements {
            self.emit_statement(statement);
        }
        if let Some(result) = &block.result {
            self.indent();
            self.emit_expression(result);
            self.push(";\n");
        }
        self.emit_defers(&defers);
    }

    fn emit_statement(&mut self, statement: &Statement) {
        self.indent();
        match statement {
            Statement::Expression(expression) => {
                if let ExpressionKind::Replace(target, value) = &expression.kind {
                    self.emit_assign_target(target);
                    self.push(" = ");
                    self.emit_expression(value);
                } else {
                    self.emit_expression(expression);
                }
                self.push(";\n");
            }
            Statement::Let {
                name,
                binding,
                declared_type,
                value,
            } => {
                let mut value_output = String::new();
                std::mem::swap(&mut self.output, &mut value_output);
                self.emit_expression(value);
                let wrap_array_early = self.is_array_newtype(declared_type.as_ref())
                    && matches!(value.kind, ExpressionKind::ArrayLiteral(_));
                std::mem::swap(&mut self.output, &mut value_output);
                let effective_name = if self.newtypes.contains_key(name) {
                    format!("_{name}")
                } else {
                    name.clone()
                };
                let emit_name = self.register_shadow(&effective_name);
                if effective_name != *name
                    && let Some(scope) = self.shadow_scopes.last_mut()
                {
                    scope.insert(name.clone(), emit_name.clone());
                }
                if matches!(binding, Binding::Variable | Binding::Reference) {
                    self.auto_ref_variables.insert(emit_name.clone());
                }
                let is_const = matches!(binding, Binding::Value | Binding::Reference);
                let ty = declared_type.as_ref().or(value.resolved_type.as_ref());
                if is_const && matches!(ty, Some(Type::Pointer(..))) {
                    self.emit_type(ty.unwrap());
                    write!(self.output, " const {emit_name}").unwrap();
                } else {
                    if is_const {
                        self.push("const ");
                    }
                    if let Some(ty) = ty {
                        self.emit_typed_name(ty, &emit_name);
                    } else {
                        write!(self.output, "auto {emit_name}").unwrap();
                    }
                }
                self.push(" = ");
                if wrap_array_early {
                    self.push("{");
                }
                self.push(&value_output);
                if wrap_array_early {
                    self.push("}");
                }
                self.push(";\n");
            }
            Statement::Assign(target, value) => {
                self.emit_assign_target(target);
                self.push(" = ");
                self.emit_expression(value);
                self.push(";\n");
            }
            Statement::Return(value) => {
                if !self.function_defers.is_empty() {
                    let defers = self.function_defers.clone();
                    for defer in defers.iter().rev() {
                        self.emit_statement(defer);
                    }
                }
                if let Some(value) = value {
                    self.push("return ");
                    self.emit_expression(value);
                    self.push(";\n");
                } else if self.in_main {
                    self.push("return 0;\n");
                } else {
                    self.push("return;\n");
                }
            }
            Statement::Label {
                name,
                parameters,
                initial_arguments,
            } => {
                for (param, arg) in parameters.iter().zip(initial_arguments) {
                    let qualified = format!("{name}_{}", param.name);
                    self.push(&qualified);
                    self.push(" = ");
                    self.emit_expression(arg);
                    self.push(";\n");
                    self.indent();
                }
                self.output.truncate(self.output.trim_end().len());
                writeln!(self.output, "\n{name}:;").unwrap();
            }
            Statement::Jump { label, arguments } => {
                if !arguments.is_empty() {
                    let Some(params) = self.labels.get(label).cloned() else {
                        eprintln!("internal error: label '{label}' not found in function");
                        return;
                    };
                    let base = self.temp_counter;
                    self.temp_counter += params.len();
                    for (index, (param, arg)) in params.iter().zip(arguments).enumerate() {
                        let temp_id = base + index;
                        if let Some(ty) = &param.parameter_type {
                            self.emit_type(ty);
                        }
                        write!(self.output, " _tmp_{temp_id} = ").unwrap();
                        self.emit_expression(arg);
                        self.push(";\n");
                        self.indent();
                    }
                    for (index, param) in params.iter().enumerate() {
                        let temp_id = base + index;
                        let qualified = self
                            .label_param_names
                            .get(&param.name)
                            .cloned()
                            .unwrap_or_else(|| param.name.clone());
                        write!(self.output, "{qualified} = _tmp_{temp_id}").unwrap();
                        self.push(";\n");
                        self.indent();
                    }
                }
                writeln!(self.output, "goto {label};").unwrap();
            }
            Statement::MultiReplace {
                bindings,
                targets,
                values,
            } => {
                let base = self.temp_counter;
                self.temp_counter += values.len();
                for (index, value) in values.iter().enumerate() {
                    let temp_id = base + index;
                    if let Some(ty) = &value.resolved_type {
                        self.emit_type(ty);
                    } else {
                        self.push("auto");
                    }
                    write!(self.output, " _swap_{temp_id} = ").unwrap();
                    self.emit_expression(value);
                    self.push(";\n");
                    self.indent();
                }
                for (index, binding) in bindings.iter().enumerate() {
                    if let Some((name, bind_mode)) = binding {
                        let is_const = matches!(bind_mode, Binding::Value | Binding::Reference);
                        if matches!(bind_mode, Binding::Variable | Binding::Reference) {
                            self.auto_ref_variables.insert(name.clone());
                        }
                        if is_const {
                            self.push("const ");
                        }
                        if let Some(ty) = &values[index].resolved_type {
                            self.emit_type(ty);
                        }
                        write!(self.output, " {name} = ").unwrap();
                        self.emit_place(&targets[index]);
                        self.push(";\n");
                        self.indent();
                    }
                }
                for (index, target) in targets.iter().enumerate() {
                    let temp_id = base + index;
                    self.emit_assign_target(target);
                    writeln!(self.output, " = _swap_{temp_id};").unwrap();
                    if index + 1 < targets.len() {
                        self.indent();
                    }
                }
            }
            Statement::Defer(_) => {}
        }
    }

    fn collect_defers(statements: &[Statement]) -> Vec<&Statement> {
        let mut defers = Vec::new();
        for statement in statements {
            if let Statement::Defer(inner) = statement {
                defers.push(inner.as_ref());
            }
        }
        defers
    }

    fn emit_defers(&mut self, defers: &[&Statement]) {
        for statement in defers.iter().rev() {
            self.emit_statement(statement);
        }
    }

    fn is_direct_auto_ref(&self, expression: &Expression) -> bool {
        matches!(&expression.kind, ExpressionKind::Variable(name) if self.auto_ref_variables.contains(self.resolve_shadow(name)))
    }

    fn is_auto_ref_chain(&self, expression: &Expression) -> bool {
        match &expression.kind {
            ExpressionKind::Variable(name) => {
                self.auto_ref_variables.contains(self.resolve_shadow(name))
            }
            ExpressionKind::Field(inner, _) | ExpressionKind::Index(inner, _) => {
                self.is_auto_ref_chain(inner)
            }
            _ => false,
        }
    }

    fn resolve_variable_name(&self, name: &str) -> String {
        self.label_param_names
            .get(name)
            .cloned()
            .unwrap_or_else(|| self.resolve_shadow(name).into())
    }

    fn is_pointer_param(&self, expression: &Expression) -> bool {
        if let ExpressionKind::Variable(name) = &expression.kind {
            let resolved = self.resolve_variable_name(name);
            self.pointer_param_variables.contains(&resolved)
        } else {
            false
        }
    }

    fn emit_assign_target(&mut self, expression: &Expression) {
        if let ExpressionKind::Variable(name) = &expression.kind {
            let resolved = self.resolve_variable_name(name);
            if self.pointer_param_variables.contains(&resolved) {
                write!(self.output, "(*{resolved})").unwrap();
                return;
            }
        }
        if let ExpressionKind::Dereference(inner) = &expression.kind
            && let ExpressionKind::Variable(name) = &inner.kind
        {
            let resolved = self.resolve_variable_name(name);
            if self.pointer_param_variables.contains(&resolved) {
                write!(self.output, "(*{resolved})").unwrap();
                return;
            }
        }
        self.emit_place(expression);
    }

    fn emit_place(&mut self, expression: &Expression) {
        match &expression.kind {
            ExpressionKind::Variable(name) => {
                let resolved = self.resolve_variable_name(name);
                self.push(&resolved);
            }
            ExpressionKind::Field(inner, field) => {
                let effective_inner = if let ExpressionKind::Field(grandchild, inner_field) =
                    &inner.kind
                {
                    if self.is_identity_downcast(grandchild.resolved_type.as_ref(), inner_field) {
                        grandchild.as_ref()
                    } else {
                        inner.as_ref()
                    }
                } else {
                    inner.as_ref()
                };
                if self.is_identity_downcast(effective_inner.resolved_type.as_ref(), field) {
                    self.emit_place(effective_inner);
                } else if self.is_typedef_downcast(effective_inner.resolved_type.as_ref()) {
                    self.push("(*(");
                    if let Some(resolved_type) = expression.resolved_type.as_ref() {
                        self.emit_type(resolved_type);
                    }
                    self.push("*)&");
                    self.emit_place(effective_inner);
                    self.push(")");
                } else {
                    self.emit_place(effective_inner);
                    let use_arrow = if let ExpressionKind::Variable(name) = &effective_inner.kind {
                        let resolved = self.resolve_variable_name(name);
                        self.pointer_param_variables.contains(&resolved)
                    } else {
                        false
                    };
                    if use_arrow
                        || (self.is_pointer_type(effective_inner.resolved_type.as_ref())
                            && !self.is_direct_auto_ref(effective_inner))
                    {
                        self.push("->");
                    } else {
                        self.push(".");
                    }
                    self.push(field);
                }
            }
            ExpressionKind::Index(array, index) => {
                self.emit_place(array);
                if self.is_array_newtype(array.resolved_type.as_ref()) {
                    self.push(".data");
                }
                self.push("[");
                self.emit_expression(index);
                self.push("]");
            }
            ExpressionKind::Dereference(inner)
                if self.is_auto_ref_chain(inner) && !self.is_pointer_param(inner) =>
            {
                self.emit_place(inner);
            }
            ExpressionKind::Dereference(inner) => {
                self.push("(*");
                self.emit_expression(inner);
                self.push(")");
            }
            _ => self.emit_expression(expression),
        }
    }
}

mod emit;

#[cfg(test)]
mod tests;