package checker

import "../ast"
import "../hir"
import "../source"
import "../symbol"
import "../target"
import "../types"
import "base:intrinsics"
import "core:fmt"
import "core:mem"
import "core:slice"
import "core:strings"

Spec_Id :: distinct u32
INVALID_SPEC :: Spec_Id(0xffff_ffff)

spec_id :: proc(index: int) -> Spec_Id {
	assert(index >= 0 && u64(index) < u64(INVALID_SPEC))
	return Spec_Id(index)
}

spec_index :: proc(id: Spec_Id, count: int) -> (int, bool) {
	index := int(id)
	return index, id != INVALID_SPEC && index < count
}

Spec :: struct {
	template: ast.Function_Id,
	args:     []types.Type,
	result:   types.Type,
	hir_id:   hir.Function_Id,
}

Infer_Local :: struct {
	name: symbol.Id,
	type: types.Type,
}

Build_Local :: struct {
	name:    symbol.Id,
	type:    types.Type,
	mutable: bool,
	id:      hir.Local_Id,
}

Constant_Kind :: enum {
	Unknown,
	Not_Constant,
	Value,
	Overflow,
}

Constant :: struct {
	kind:  Constant_Kind,
	value: i128,
}

Function_Index_Entry :: struct {
	scope: ast.Package_Id,
	name:  symbol.Id,
	id:    ast.Function_Id,
}

Global_Index_Entry :: struct {
	scope: ast.Package_Id,
	name:  symbol.Id,
	id:    ast.Global_Id,
}

Import_Index_Entry :: struct {
	scope: ast.File_Id,
	name:  symbol.Id,
	id:    ast.Import_Id,
}

Checker :: struct {
	ast_module:           ^ast.Module,
	diagnostics:          ^source.Diagnostics,
	symbols:              ^symbol.Table,
	module:               hir.Module,
	specs:                [dynamic]Spec,
	function_index:       []Function_Index_Entry,
	global_index:         []Global_Index_Entry,
	import_index:         []Import_Index_Entry,
	global_types:         []types.Type,
	constants:            []Constant,
	template_diagnostics: []source.Diagnostic_Id,
	constant_stack:       [dynamic]Constant_Frame,
	ast_expr_stack:       [dynamic]ast.Expr_Id,
	hir_expr_stack:       [dynamic]hir.Expr_Id,
	infer_stack:          [dynamic]Infer_Frame,
	build_stack:          [dynamic]Build_Expr_Frame,
	cycle_stack:          [dynamic]Cycle_Frame,
	main_symbol:          symbol.Id,
	sink_symbol:          symbol.Id,
	target:               target.Target,
	allocator:            mem.Allocator,
}

symbol_text :: proc(checker: ^Checker, id: symbol.Id) -> string {
	return symbol.resolve(checker.symbols, id)
}

Constant_Frame :: struct {
	expr:  ast.Expr_Id,
	stage: u8,
}

eval_constant :: proc(checker: ^Checker, expr_id: ast.Expr_Id) -> Constant {
	if expr_id == ast.INVALID_EXPR || int(expr_id) >= len(checker.ast_module.exprs) {
		return Constant{kind = .Not_Constant}
	}
	stack := checker.constant_stack
	clear_dynamic_array(&stack)
	defer {
		clear_dynamic_array(&stack)
		checker.constant_stack = stack
	}
	append(&stack, Constant_Frame{expr=expr_id})

	for len(stack) > 0 {
		frame_index := len(stack)-1
		frame := stack[frame_index]
		if checker.constants[frame.expr].kind != .Unknown {
			_ = pop(&stack)
			continue
		}
		expr := checker.ast_module.exprs[frame.expr]
		if expr.kind != .Add && expr.kind != .Negate {
			result := Constant{kind = .Not_Constant}
			if expr.kind == .Integer {
				result = Constant{kind = .Value, value = i128(expr.integer)}
			}
			checker.constants[frame.expr] = result
			_ = pop(&stack)
			continue
		}
		if frame.stage == 0 {
			stack[frame_index].stage = 1
			if expr.left != ast.INVALID_EXPR && int(expr.left) < len(checker.ast_module.exprs) &&
			   checker.constants[expr.left].kind == .Unknown {
				append(&stack, Constant_Frame{expr=expr.left})
			}
			continue
		}
		if frame.stage == 1 && expr.kind == .Negate {
			operand := Constant{kind = .Not_Constant}
			if expr.left != ast.INVALID_EXPR && int(expr.left) < len(checker.constants) {
				operand = checker.constants[expr.left]
			}
			result := Constant{kind = .Not_Constant}
			if operand.kind == .Overflow {
				result = Constant{kind = .Overflow}
			} else if operand.kind == .Value {
				value, overflow := intrinsics.overflow_sub(i128(0), operand.value)
				result = Constant{kind = .Overflow} if overflow else Constant{kind = .Value, value = value}
			}
			checker.constants[frame.expr] = result
			_ = pop(&stack)
			continue
		}
		if frame.stage == 1 {
			stack[frame_index].stage = 2
			if expr.right != ast.INVALID_EXPR && int(expr.right) < len(checker.ast_module.exprs) &&
			   checker.constants[expr.right].kind == .Unknown {
				append(&stack, Constant_Frame{expr=expr.right})
			}
			continue
		}
		left := Constant{kind = .Not_Constant}
		right := Constant{kind = .Not_Constant}
		if expr.left != ast.INVALID_EXPR && int(expr.left) < len(checker.constants) {
			left = checker.constants[expr.left]
		}
		if expr.right != ast.INVALID_EXPR && int(expr.right) < len(checker.constants) {
			right = checker.constants[expr.right]
		}
		result := Constant{kind = .Not_Constant}
		if left.kind == .Overflow || right.kind == .Overflow {
			result = Constant{kind = .Overflow}
		} else if left.kind == .Value && right.kind == .Value {
			value, overflow := intrinsics.overflow_add(left.value, right.value)
			result = Constant{kind = .Overflow} if overflow else Constant{kind = .Value, value = value}
		}
		checker.constants[frame.expr] = result
		_ = pop(&stack)
	}
	return checker.constants[expr_id]
}

fits_signed_type :: proc(value: i128, value_type: types.Type, selected := target.DEFAULT) -> bool {
	if !types.is_signed(value_type, selected) {
		return false
	}
	limit := i128(1) << u32(types.bits(value_type, selected) - 1)
	return value >= -limit && value < limit
}

fits_unsigned_type :: proc(value: i128, value_type: types.Type, selected := target.DEFAULT) -> bool {
	if !types.is_unsigned(value_type, selected) || value < 0 {
		return false
	}
	limit := i128(1) << u32(types.bits(value_type, selected))
	return value < limit
}

fits_integer_type :: proc(value: i128, value_type: types.Type, selected := target.DEFAULT) -> bool {
	return fits_signed_type(value, value_type, selected) || fits_unsigned_type(value, value_type, selected)
}

fits_i64 :: proc(value: i128) -> bool {
	return fits_signed_type(value, types.I64)
}

type_from_syntax :: proc(value: ast.Type_Syntax) -> types.Type {
	return value
}

is_runtime_type :: proc(checker: ^Checker, value: types.Type) -> bool {
	return types.is_runtime_value(value, &checker.module.types)
}

resolve_inferred_array :: proc(checker: ^Checker, value: types.Type, expr_id: ast.Expr_Id) -> types.Type {
	item, ok := types.node(&checker.module.types, value)
	if !ok || item.kind != .Array || !item.inferred_count ||
	   expr_id == ast.INVALID_EXPR || int(expr_id) >= len(checker.ast_module.exprs) {
		return value
	}
	expr := checker.ast_module.exprs[expr_id]
	if expr.kind != .Array {
		return value
	}
	return types.with_array_count(&checker.module.types, value, u64(len(expr.args)))
}

function_index_less :: proc(left, right: Function_Index_Entry) -> bool {
	if left.scope != right.scope {
		return left.scope < right.scope
	}
	if left.name != right.name {
		return int(left.name) < int(right.name)
	}
	return left.id < right.id
}

global_index_less :: proc(left, right: Global_Index_Entry) -> bool {
	if left.scope != right.scope {
		return left.scope < right.scope
	}
	if left.name != right.name {
		return int(left.name) < int(right.name)
	}
	return left.id < right.id
}

import_index_less :: proc(left, right: Import_Index_Entry) -> bool {
	if left.scope != right.scope {
		return left.scope < right.scope
	}
	if left.name != right.name {
		return int(left.name) < int(right.name)
	}
	return left.id < right.id
}

find_function_symbol :: proc(index: []Function_Index_Entry, scope: ast.Package_Id, name: symbol.Id) -> ast.Function_Id {
	low := 0
	high := len(index)
	for low < high {
		middle := low + (high-low)/2
		entry := index[middle]
		if entry.scope < scope || entry.scope == scope && int(entry.name) < int(name) {
			low = middle + 1
		} else {
			high = middle
		}
	}
	if low < len(index) && index[low].scope == scope && index[low].name == name {
		return index[low].id
	}
	return ast.INVALID_FUNCTION
}

find_global_symbol :: proc(index: []Global_Index_Entry, scope: ast.Package_Id, name: symbol.Id) -> ast.Global_Id {
	low := 0
	high := len(index)
	for low < high {
		middle := low + (high-low)/2
		entry := index[middle]
		if entry.scope < scope || entry.scope == scope && int(entry.name) < int(name) {
			low = middle + 1
		} else {
			high = middle
		}
	}
	if low < len(index) && index[low].scope == scope && index[low].name == name {
		return index[low].id
	}
	return ast.INVALID_GLOBAL
}

find_import_symbol :: proc(index: []Import_Index_Entry, scope: ast.File_Id, name: symbol.Id) -> ast.Import_Id {
	low := 0
	high := len(index)
	for low < high {
		middle := low + (high-low)/2
		entry := index[middle]
		if entry.scope < scope || entry.scope == scope && int(entry.name) < int(name) {
			low = middle + 1
		} else {
			high = middle
		}
	}
	if low < len(index) && index[low].scope == scope && index[low].name == name {
		return index[low].id
	}
	return ast.INVALID_IMPORT
}

build_symbol_indexes :: proc(checker: ^Checker) {
	checker.function_index = make([]Function_Index_Entry, len(checker.ast_module.functions), checker.allocator)
	for function, id in checker.ast_module.functions {
		checker.function_index[id] = Function_Index_Entry{scope=function.pkg, name=function.name, id=ast.function_id(id)}
	}
	slice.sort_by(checker.function_index, function_index_less)

	checker.global_index = make([]Global_Index_Entry, len(checker.ast_module.globals), checker.allocator)
	for global, id in checker.ast_module.globals {
		checker.global_index[id] = Global_Index_Entry{scope=global.pkg, name=global.name, id=ast.global_id(id)}
	}
	slice.sort_by(checker.global_index, global_index_less)

	checker.import_index = make([]Import_Index_Entry, len(checker.ast_module.imports), checker.allocator)
	for import_item, id in checker.ast_module.imports {
		checker.import_index[id] = Import_Index_Entry{scope=import_item.file, name=import_item.alias, id=ast.import_id(id)}
	}
	slice.sort_by(checker.import_index, import_index_less)
}

find_template :: proc(checker: ^Checker, name: symbol.Id, pkg := ast.Package_Id(0)) -> ast.Function_Id {
	return find_function_symbol(checker.function_index, pkg, name)
}

find_global :: proc(checker: ^Checker, name: symbol.Id, pkg := ast.Package_Id(0)) -> ast.Global_Id {
	return find_global_symbol(checker.global_index, pkg, name)
}

find_import :: proc(checker: ^Checker, file: ast.File_Id, alias: symbol.Id, mark_used := false) -> ast.Import_Id {
	id := find_import_symbol(checker.import_index, file, alias)
	if id != ast.INVALID_IMPORT && mark_used {
		checker.ast_module.imports[id].used = true
	}
	return id
}

expr_package :: proc(checker: ^Checker, expr: ast.Expr, pkg: ast.Package_Id, file: ast.File_Id, mark_used := false) -> (ast.Package_Id, bool) {
	if !symbol.is_valid(expr.qualifier) {
		return pkg, true
	}
	import_id := find_import(checker, file, expr.qualifier, mark_used)
	if import_id == ast.INVALID_IMPORT {
		return ast.INVALID_PACKAGE, false
	}
	import_item := checker.ast_module.imports[import_id]
	if import_item.target == ast.INVALID_PACKAGE || int(import_item.target) >= len(checker.ast_module.packages) ||
	   !checker.ast_module.packages[import_item.target].available {
		return import_item.target, false
	}
	return import_item.target, true
}

add_package_resolution_diagnostic :: proc(checker: ^Checker, expr: ast.Expr, file: ast.File_Id) -> source.Diagnostic_Id {
	if find_import(checker, file, expr.qualifier) == ast.INVALID_IMPORT {
		return source.addf(checker.diagnostics, expr.span, "unknown package alias '%s'", symbol_text(checker, expr.qualifier))
	}
	return source.addf(checker.diagnostics, expr.span, "unavailable imported package '%s'", symbol_text(checker, expr.qualifier))
}

add_name_resolution_diagnostic :: proc(checker: ^Checker, expr: ast.Expr, target_pkg: ast.Package_Id) -> source.Diagnostic_Id {
	if find_template(checker, expr.name, target_pkg) != ast.INVALID_FUNCTION {
		return source.addf(checker.diagnostics, expr.span, "'%s' is a function, not a global value", symbol_text(checker, expr.name))
	}
	if symbol.is_valid(expr.qualifier) {
		return source.addf(
			checker.diagnostics,
			expr.span,
			"package '%s' has no member '%s'",
			symbol_text(checker, expr.qualifier),
			symbol_text(checker, expr.name),
		)
	}
	return source.addf(checker.diagnostics, expr.span, "unresolved global '%s'", symbol_text(checker, expr.name))
}

add_call_resolution_diagnostic :: proc(checker: ^Checker, expr: ast.Expr, target_pkg: ast.Package_Id) -> source.Diagnostic_Id {
	if find_global(checker, expr.name, target_pkg) != ast.INVALID_GLOBAL {
		return source.addf(checker.diagnostics, expr.span, "'%s' is a global, not a function", symbol_text(checker, expr.name))
	}
	if symbol.is_valid(expr.qualifier) {
		return source.addf(
			checker.diagnostics,
			expr.span,
			"package '%s' has no member '%s'",
			symbol_text(checker, expr.qualifier),
			symbol_text(checker, expr.name),
		)
	}
	return source.addf(checker.diagnostics, expr.span, "unresolved function '%s'", symbol_text(checker, expr.name))
}

contains_name :: proc(names: []symbol.Id, name: symbol.Id) -> bool {
	for existing in names {
		if existing == name {
			return true
		}
	}
	return false
}

mark_expr_imports_used :: proc(checker: ^Checker, expr_id: ast.Expr_Id, file: ast.File_Id) {
	stack := checker.ast_expr_stack
	clear_dynamic_array(&stack)
	defer {
		clear_dynamic_array(&stack)
		checker.ast_expr_stack = stack
	}
	append(&stack, expr_id)
	for len(stack) > 0 {
		id := pop(&stack)
		if id == ast.INVALID_EXPR || int(id) >= len(checker.ast_module.exprs) {
			continue
		}
		expr := checker.ast_module.exprs[id]
		if (expr.kind == .Name || expr.kind == .Call) && symbol.is_valid(expr.qualifier) {
			_ = find_import(checker, file, expr.qualifier, true)
		}
		switch expr.kind {
		case .Call:
			append(&stack, ..expr.args)
		case .Array, .Struct_Literal, .Slice:
			append(&stack, ..expr.args)
			if expr.left != ast.INVALID_EXPR {
				append(&stack, expr.left)
			}
		case .Negate, .Address, .Deref, .Field, .Unwrap, .Keyed:
			append(&stack, expr.left)
		case .Add, .Index, .Orelse:
			append(&stack, expr.left, expr.right)
		case .Invalid, .Integer, .Float, .String, .None, .Name:
		}
	}
}

validate_declarations :: proc(checker: ^Checker) {
	for function, function_id in checker.ast_module.functions {
		locals: [dynamic]symbol.Id
		locals.allocator = checker.allocator
		for param in function.params {
			if param.type == types.VOID {
				source.add(
					checker.diagnostics,
					param.span,
					"void is only valid as a function result type",
				)
			}
			if contains_name(locals[:], param.name) {
				source.addf(
					checker.diagnostics,
					param.span,
					"duplicate parameter '%s'",
					symbol_text(checker, param.name),
				)
			}
			append(&locals, param.name)
			if types.contains_c_struct_by_value(type_from_syntax(param.type), &checker.module.types) {
				checker.template_diagnostics[function_id] = source.addf(
					checker.diagnostics,
					param.span,
					"C records cannot be passed by value to '%s'",
					symbol_text(checker, function.name),
				)
			}
		}
		if types.contains_c_struct_by_value(type_from_syntax(function.result), &checker.module.types) {
			checker.template_diagnostics[function_id] = source.addf(
				checker.diagnostics,
				function.span,
				"C records cannot be returned by value from '%s'",
				symbol_text(checker, function.name),
			)
		}
		if !function.has_body && !function.c_abi {
			checker.template_diagnostics[function_id] = source.addf(
				checker.diagnostics,
				function.span,
				"bodyless function '%s' must use 'c_func'",
				symbol_text(checker, function.name),
			)
		}
		if !function.has_body && function.c_abi {
			for param in function.params {
				if !types.is_c_signature_type(type_from_syntax(param.type), &checker.module.types) {
					checker.template_diagnostics[function_id] = source.addf(
						checker.diagnostics,
						param.span,
						"foreign function '%s' requires concrete parameter types",
						symbol_text(checker, function.name),
					)
				}
			}
			result := type_from_syntax(function.result)
			if !types.is_c_signature_type(result, &checker.module.types, true) {
				checker.template_diagnostics[function_id] = source.addf(
					checker.diagnostics,
					function.span,
					"foreign function '%s' requires a concrete or void result type",
					symbol_text(checker, function.name),
				)
			}
			if function.pkg == 0 && function.name == checker.main_symbol {
				checker.template_diagnostics[function_id] = source.add(
					checker.diagnostics,
					function.span,
					"main must have a body",
				)
			}
		}
		for statement_id in function.body {
			statement := checker.ast_module.statements[statement_id]
			switch statement.kind {
			case .Declaration, .Assignment, .Return, .Expression:
				mark_expr_imports_used(checker, statement.expr, function.file)
				if statement.target != ast.INVALID_EXPR {
					mark_expr_imports_used(checker, statement.target, function.file)
				}
			case .Invalid:
			}
		}
		delete(locals)
	}
	for function, function_id in checker.ast_module.functions {
		if function.has_body || !function.c_abi {
			continue
		}
		for other, other_id in checker.ast_module.functions {
			if other_id == function_id || other.has_body || !other.c_abi || other.name != function.name {
				continue
			}
			checker.template_diagnostics[function_id] = source.addf(
				checker.diagnostics,
				function.span,
				"duplicate foreign symbol '%s'",
				symbol_text(checker, function.name),
			)
			break
		}
	}
}

validate_type_nodes :: proc(checker: ^Checker) {
	for item, index in checker.module.types.nodes {
		id := types.DYNAMIC_START+types.Type(index)
		if item.has_sentinel {
			value := i128(item.sentinel)
			if types.is_signed(item.child, checker.target) {
				value = i128(i64(item.sentinel))
			}
			if !types.is_concrete_integer(item.child) || !fits_integer_type(value, item.child, checker.target) {
				source.addf(
					checker.diagnostics,
					source.Span{},
					"sentinel value does not fit array or slice element type %s",
					types.name(item.child),
				)
			}
		}
		if item.kind == .Struct {
			for field in types.fields_for(&checker.module.types, id) {
				if types.contains_c_struct_by_value(field.type, &checker.module.types) {
					source.add(
						checker.diagnostics,
						source.Span{},
						"C records may only appear behind pointers",
					)
				}
			}
		}
	}
}

find_infer_local :: proc(locals: []Infer_Local, name: symbol.Id) -> types.Type {
	for index := len(locals) - 1; index >= 0; index -= 1 {
		if locals[index].name == name {
			return locals[index].type
		}
	}
	return types.INVALID
}

find_spec :: proc(checker: ^Checker, template: ast.Function_Id, actual_args: []types.Type) -> Spec_Id {
	function := checker.ast_module.functions[template]
	for spec, index in checker.specs {
		if spec.template != template || len(spec.args) != len(function.params) {
			continue
		}
		matches := true
		for param, param_index in function.params {
			actual := types.INVALID
			if param_index < len(actual_args) {
				actual = actual_args[param_index]
			}
			if !types.equal(spec.args[param_index], specialized_param_type(param.type, actual)) {
				matches = false
				break
			}
		}
		if matches {
			return spec_id(index)
		}
	}
	return INVALID_SPEC
}

specialized_param_type :: proc(syntax: ast.Type_Syntax, actual: types.Type) -> types.Type {
	declared := type_from_syntax(syntax)
	if types.is_constraint(declared) {
		return actual
	}
	return declared
}

can_specialize :: proc(checker: ^Checker, function: ast.Function, actual_args: []types.Type) -> bool {
	for param, index in function.params {
		actual := types.INVALID
		if index < len(actual_args) {
			actual = actual_args[index]
		}
		if !is_runtime_type(checker, specialized_param_type(param.type, actual)) {
			return false
		}
	}
	return true
}

ensure_spec :: proc(checker: ^Checker, template: ast.Function_Id, actual_args: []types.Type) -> Spec_Id {
	if existing := find_spec(checker, template, actual_args); existing != INVALID_SPEC {
		return existing
	}
	function := checker.ast_module.functions[template]
	signature: [dynamic]types.Type
	signature.allocator = checker.allocator
	for param, index in function.params {
		actual := types.INVALID
		if index < len(actual_args) {
			actual = actual_args[index]
		}
		append(&signature, specialized_param_type(param.type, actual))
	}
	result := type_from_syntax(function.result)
	if function.pkg == 0 && function.name == checker.main_symbol && function.result == types.INT {
		result = types.I32
	}
	index := spec_id(len(checker.specs))
	append(
		&checker.specs,
		Spec{template = template, args = signature[:], result = result, hir_id = hir.INVALID_FUNCTION},
	)
	return index
}

mark_spec_demanded :: proc(checker: ^Checker, id: Spec_Id, stack: ^[dynamic]Spec_Id) {
	if id == INVALID_SPEC || checker.specs[id].hir_id != hir.INVALID_FUNCTION {
		return
	}
	checker.specs[id].hir_id = hir.Function_Id(0)
	append(stack, id)
}

Infer_Frame :: struct {
	expr:      ast.Expr_Id,
	stage:     u8,
	left:      types.Type,
	arg_index: int,
	args:      []types.Type,
	template:  ast.Function_Id,
}

infer_nested_expr :: proc(
	checker: ^Checker,
	expr_id: ast.Expr_Id,
	locals: []Infer_Local,
	pkg: ast.Package_Id,
	file: ast.File_Id,
	demanded: ^[dynamic]Spec_Id,
) -> types.Type {
	outer := checker.infer_stack
	checker.infer_stack = nil
	checker.infer_stack.allocator = checker.allocator
	result := infer_expr(checker, expr_id, locals, pkg, file, demanded)
	delete(checker.infer_stack)
	checker.infer_stack = outer
	return result
}

infer_compound_expr :: proc(
	checker: ^Checker,
	expr: ast.Expr,
	locals: []Infer_Local,
	pkg: ast.Package_Id,
	file: ast.File_Id,
	demanded: ^[dynamic]Spec_Id,
) -> types.Type {
	store := &checker.module.types
	#partial switch expr.kind {
	case .String:
		return types.slice(store, types.U8, false, true, 0)
	case .Array:
		element := types.INVALID
		for arg in expr.args {
			actual := infer_nested_expr(checker, arg, locals, pkg, file, demanded)
			if !types.is_valid(element) {
				element = actual
			} else if !types.equal(element, actual) {
				element = types.widest(element, actual)
			}
		}
		if !types.is_valid(element) {
			element = types.I64
		}
		return types.array(store, element, u64(len(expr.args)), false)
	case .None:
		return types.INVALID
	case .Address:
		child := infer_nested_expr(checker, expr.left, locals, pkg, file, demanded)
		return types.pointer(store, child, false, false)
	case .Deref:
		value := infer_nested_expr(checker, expr.left, locals, pkg, file, demanded)
		return types.child_type(value, store) if types.is_pointer(value, store) else types.INVALID
	case .Index:
		value := infer_nested_expr(checker, expr.left, locals, pkg, file, demanded)
		_ = infer_nested_expr(checker, expr.right, locals, pkg, file, demanded)
		return types.child_type(value, store)
	case .Slice:
		value := infer_nested_expr(checker, expr.left, locals, pkg, file, demanded)
		item, ok := types.node(store, value)
		if !ok || (item.kind != .Array && item.kind != .Slice) {
			return types.INVALID
		}
		for bound in expr.args {
			if bound != ast.INVALID_EXPR {
				_ = infer_nested_expr(checker, bound, locals, pkg, file, demanded)
			}
		}
		preserve := item.has_sentinel && expr.args[1] == ast.INVALID_EXPR
		return types.slice(store, item.child, item.mutable, preserve, item.sentinel)
	case .Field:
		value := infer_nested_expr(checker, expr.left, locals, pkg, file, demanded)
		item, has_item := types.node(store, value)
		field_name := symbol_text(checker, expr.name)
		if has_item && (item.kind == .Array || item.kind == .Slice) {
			if field_name == "len" {
				return types.USIZE
			}
			if field_name == "ptr" {
				return types.pointer(store, item.child, item.mutable, true)
			}
		}
		if types.is_pointer(value, store) {
			value = types.child_type(value, store)
		}
		_, field, ok := find_struct_field(checker, value, expr.name)
		return field.type if ok else types.INVALID
	case .Unwrap:
		value := infer_nested_expr(checker, expr.left, locals, pkg, file, demanded)
		return types.child_type(value, store) if types.is_optional(value, store) else types.INVALID
	case .Orelse:
		value := infer_nested_expr(checker, expr.left, locals, pkg, file, demanded)
		_ = infer_nested_expr(checker, expr.right, locals, pkg, file, demanded)
		return types.child_type(value, store) if types.is_optional(value, store) else types.INVALID
	case .Struct_Literal:
		for keyed in expr.args {
			_ = infer_nested_expr(checker, checker.ast_module.exprs[keyed].left, locals, pkg, file, demanded)
		}
		target_pkg, available := expr_package(checker, expr, pkg, file)
		return types.find_named(store, u32(target_pkg), u32(expr.name)) if available else types.INVALID
	case .Keyed:
		return infer_nested_expr(checker, expr.left, locals, pkg, file, demanded)
	case:
		return types.INVALID
	}
}

infer_expr :: proc(
	checker: ^Checker,
	expr_id: ast.Expr_Id,
	locals: []Infer_Local,
	pkg := ast.Package_Id(0),
	file := ast.File_Id(0),
	demanded: ^[dynamic]Spec_Id = nil,
) -> types.Type {
	stack := checker.infer_stack
	clear_dynamic_array(&stack)
	defer {
		for frame in stack {
			delete(frame.args, checker.allocator)
		}
		clear_dynamic_array(&stack)
		checker.infer_stack = stack
	}
	append(&stack, Infer_Frame{expr=expr_id, template=ast.INVALID_FUNCTION})
	last := types.INVALID

	for len(stack) > 0 {
		frame_index := len(stack)-1
		frame := stack[frame_index]
		if frame.expr == ast.INVALID_EXPR || int(frame.expr) >= len(checker.ast_module.exprs) {
			last = types.INVALID
			_ = pop(&stack)
			continue
		}
		expr := checker.ast_module.exprs[frame.expr]
		if frame.stage == 0 {
			constant := eval_constant(checker, frame.expr)
			if constant.kind == .Overflow || (constant.kind == .Value && !fits_i64(constant.value)) {
				last = types.I64
				_ = pop(&stack)
				continue
			}
			if constant.kind == .Value {
				last = types.smallest_signed_for_literal(i64(constant.value))
				_ = pop(&stack)
				continue
			}
			switch expr.kind {
			case .Invalid:
				last = types.INVALID
				_ = pop(&stack)
			case .Integer:
				last = types.I64
				if expr.integer <= 0x7fff_ffff_ffff_ffff {
					last = types.smallest_signed_for_literal(i64(expr.integer))
				}
				_ = pop(&stack)
			case .Float:
				last = types.F64
				_ = pop(&stack)
			case .String, .Array, .None, .Address, .Deref, .Index, .Slice,
			     .Field, .Unwrap, .Orelse, .Struct_Literal, .Keyed:
				last = infer_compound_expr(checker, expr, locals, pkg, file, demanded)
				_ = pop(&stack)
			case .Name:
				last = types.INVALID
				if !symbol.is_valid(expr.qualifier) {
					last = find_infer_local(locals, expr.name)
				} else {
					base_type := find_infer_local(locals, expr.qualifier)
					item, has_item := types.node(&checker.module.types, base_type)
					field_name := symbol_text(checker, expr.name)
					if has_item && (item.kind == .Array || item.kind == .Slice) {
						if field_name == "len" {
							last = types.USIZE
						} else if field_name == "ptr" {
							last = types.pointer(&checker.module.types, item.child, item.mutable, true)
						}
					}
					if types.is_pointer(base_type, &checker.module.types) {
						base_type = types.child_type(base_type, &checker.module.types)
					}
					if !types.is_valid(last) {
						_, field, ok := find_struct_field(checker, base_type, expr.name)
						if ok {
							last = field.type
						}
					}
				}
				if !types.is_valid(last) {
					target_pkg, available := expr_package(checker, expr, pkg, file)
					if available {
						global := find_global(checker, expr.name, target_pkg)
						if global != ast.INVALID_GLOBAL {
							last = checker.global_types[global]
						}
					}
				}
				_ = pop(&stack)
			case .Negate:
				stack[frame_index].stage = 5
				append(&stack, Infer_Frame{expr=expr.left, template=ast.INVALID_FUNCTION})
			case .Add:
				stack[frame_index].stage = 1
				append(&stack, Infer_Frame{expr=expr.left, template=ast.INVALID_FUNCTION})
			case .Call:
				target_pkg, available := expr_package(checker, expr, pkg, file)
				template := ast.INVALID_FUNCTION
				if available {
					template = find_template(checker, expr.name, target_pkg)
				}
				if template == ast.INVALID_FUNCTION {
					last = types.INVALID
					_ = pop(&stack)
					continue
				}
				if checker.template_diagnostics[template] != source.INVALID_DIAGNOSTIC {
					declared := type_from_syntax(checker.ast_module.functions[template].result)
					last = declared if is_runtime_type(checker, declared) || types.is_void(declared) else types.INVALID
					_ = pop(&stack)
					continue
				}
				stack[frame_index].template = template
				stack[frame_index].args = make([]types.Type, len(expr.args), checker.allocator)
				stack[frame_index].stage = 3
				if len(expr.args) > 0 {
					append(&stack, Infer_Frame{expr=expr.args[0], template=ast.INVALID_FUNCTION})
				}
			}
			continue
		}
		if frame.stage == 5 {
			if !types.is_signed(last, checker.target) && !types.is_float(last, checker.target) {
				last = types.INVALID
			}
			_ = pop(&stack)
			continue
		}
		if frame.stage == 1 {
			stack[frame_index].left = last
			stack[frame_index].stage = 2
			append(&stack, Infer_Frame{expr=expr.right, template=ast.INVALID_FUNCTION})
			continue
		}
		if frame.stage == 2 {
			if types.is_many_pointer(frame.left, &checker.module.types) && types.is_concrete_integer(last) {
				last = frame.left
			} else {
				last = types.widest(frame.left, last)
			}
			_ = pop(&stack)
			continue
		}
		if frame.stage == 3 {
			if frame.arg_index < len(expr.args) {
				stack[frame_index].args[frame.arg_index] = last
				stack[frame_index].arg_index += 1
				if frame.arg_index+1 < len(expr.args) {
					append(&stack, Infer_Frame{expr=expr.args[frame.arg_index+1], template=ast.INVALID_FUNCTION})
					continue
				}
			}
			function := checker.ast_module.functions[frame.template]
			if can_specialize(checker, function, stack[frame_index].args) {
				spec := INVALID_SPEC
				if demanded == nil {
					spec = ensure_spec(checker, frame.template, stack[frame_index].args)
				} else if len(expr.args) == len(function.params) {
					spec = find_spec(checker, frame.template, stack[frame_index].args)
					mark_spec_demanded(checker, spec, demanded)
				}
				if spec != INVALID_SPEC {
					last = checker.specs[spec].result
				} else {
					declared := type_from_syntax(function.result)
					last = declared if is_runtime_type(checker, declared) || types.is_void(declared) else types.INVALID
				}
			} else {
				declared := type_from_syntax(function.result)
				if function.pkg == 0 && function.name == checker.main_symbol && function.result == types.INT {
					last = types.I32
				} else {
					last = declared if is_runtime_type(checker, declared) || types.is_void(declared) else types.INVALID
				}
			}
			delete(stack[frame_index].args, checker.allocator)
			stack[frame_index].args = nil
			_ = pop(&stack)
		}
	}
	return last
}

infer_spec_result :: proc(checker: ^Checker, id: Spec_Id, demanded: ^[dynamic]Spec_Id = nil) -> types.Type {
	spec := checker.specs[id]
	function := checker.ast_module.functions[spec.template]
	declared := type_from_syntax(function.result)
	if function.pkg == 0 && function.name == checker.main_symbol && function.result == types.INT {
		declared = types.I32
	}

	locals: [dynamic]Infer_Local
	locals.allocator = checker.allocator
	defer delete(locals)
	for param, index in function.params {
		param_type := types.INVALID
		if index < len(spec.args) {
			param_type = spec.args[index]
		}
		append(&locals, Infer_Local{name = param.name, type = param_type})
	}

	result := types.INVALID
	for statement_id in function.body {
		statement := checker.ast_module.statements[statement_id]
		#partial switch statement.kind {
		case .Declaration:
			value_type := infer_expr(checker, statement.expr, locals[:], function.pkg, function.file, demanded)
			declared_local := type_from_syntax(statement.type)
			if is_runtime_type(checker, declared_local) {
				value_type = declared_local
			}
			append(&locals, Infer_Local{name = statement.name, type = value_type})
		case .Assignment, .Expression:
			if statement.target != ast.INVALID_EXPR {
				_ = infer_expr(checker, statement.target, locals[:], function.pkg, function.file, demanded)
			}
			_ = infer_expr(checker, statement.expr, locals[:], function.pkg, function.file, demanded)
		case .Return:
			if statement.expr != ast.INVALID_EXPR {
				returned := infer_expr(checker, statement.expr, locals[:], function.pkg, function.file, demanded)
				if !types.is_valid(result) {
					result = returned
				} else {
					result = types.widest(result, returned)
				}
			}
		}
	}
	if types.is_constraint(declared) {
		return result
	}
	return declared
}

merge_inferred_type :: proc(store: ^types.Store, current: ^types.Type, inferred: types.Type) -> bool {
	if !types.is_runtime_value(inferred, store) {
		return false
	}
	if !types.is_runtime_value(current^, store) {
		current^ = inferred
		return true
	}
	if types.equal(current^, inferred) {
		return false
	}
	merged := types.widest(current^, inferred)
	if types.is_concrete_scalar(merged) && !types.equal(current^, merged) {
		current^ = merged
		return true
	}
	return false
}

infer_all :: proc(checker: ^Checker) {
	for global, index in checker.ast_module.globals {
		declared := type_from_syntax(global.type)
		if is_runtime_type(checker, declared) {
			checker.global_types[index] = declared
		}
	}

	main_template := find_template(checker, checker.main_symbol, 0)
	if main_template != ast.INVALID_FUNCTION {
		ensure_spec(checker, main_template, nil)
	}

	for {
		changed := false
		spec_count := len(checker.specs)
		for global, index in checker.ast_module.globals {
			inferred := infer_expr(checker, global.expr, nil, global.pkg, global.file)
			if is_runtime_type(checker, type_from_syntax(global.type)) {
				continue
			}
			changed = merge_inferred_type(&checker.module.types, &checker.global_types[index], inferred) || changed
		}
		for index := 0; index < len(checker.specs); index += 1 {
			id := spec_id(index)
			inferred := infer_spec_result(checker, id)
			changed = merge_inferred_type(&checker.module.types, &checker.specs[id].result, inferred) || changed
		}
		if len(checker.specs) != spec_count {
			changed = true
		}
		if !changed {
			break
		}
	}
}

prune_specs :: proc(checker: ^Checker) {
	stack: [dynamic]Spec_Id
	stack.allocator = checker.allocator
	defer delete(stack)

	main_template := find_template(checker, checker.main_symbol, 0)
	if main_template != ast.INVALID_FUNCTION {
		mark_spec_demanded(checker, find_spec(checker, main_template, nil), &stack)
	}
	for global in checker.ast_module.globals {
		_ = infer_expr(checker, global.expr, nil, global.pkg, global.file, &stack)
	}
	for len(stack) > 0 {
		id := pop(&stack)
		_ = infer_spec_result(checker, id, &stack)
	}

	retained := 0
	for spec in checker.specs {
		if spec.hir_id == hir.INVALID_FUNCTION {
			delete(spec.args, checker.allocator)
			continue
		}
		checker.specs[retained] = spec
		checker.specs[retained].hir_id = hir.function_id(retained)
		retained += 1
	}
	for len(checker.specs) > retained {
		_ = pop(&checker.specs)
	}
}

add_hir_expr :: proc(checker: ^Checker, expr: hir.Expr) -> hir.Expr_Id {
	id := hir.expr_id(len(checker.module.exprs))
	append(&checker.module.exprs, expr)
	return id
}

invalid_hir_expr :: proc(
	checker: ^Checker,
	span: source.Span,
	diagnostic: source.Diagnostic_Id,
	recovery_type := types.INVALID,
) -> hir.Expr_Id {
	return add_hir_expr(
		checker,
		hir.Expr {
			kind = .Invalid,
			span = span,
			type = recovery_type,
			target = hir.INVALID_REF,
			left = hir.INVALID_EXPR,
			right = hir.INVALID_EXPR,
			diagnostic = diagnostic,
		},
	)
}

add_unique_global :: proc(values: ^[dynamic]hir.Global_Id, value: hir.Global_Id) {
	for existing in values {
		if existing == value {
			return
		}
	}
	append(values, value)
}

add_unique_function :: proc(values: ^[dynamic]hir.Function_Id, value: hir.Function_Id) {
	for existing in values {
		if existing == value {
			return
		}
	}
	append(values, value)
}

find_build_local :: proc(locals: []Build_Local, name: symbol.Id) -> (Build_Local, bool) {
	for index := len(locals) - 1; index >= 0; index -= 1 {
		if locals[index].name == name {
			return locals[index], true
		}
	}
	return Build_Local{}, false
}

coerce_expr :: proc(
	checker: ^Checker,
	expr_id: hir.Expr_Id,
	expected: types.Type,
	span: source.Span,
) -> hir.Expr_Id {
	if expr_id == hir.INVALID_EXPR {
		return expr_id
	}
	actual := checker.module.exprs[expr_id].type
	if types.equal(actual, expected) {
		return expr_id
	}
	if types.can_weaken_pointer(actual, expected, &checker.module.types) {
		checker.module.exprs[expr_id].type = expected
		return expr_id
	}
	if types.is_optional(expected, &checker.module.types) {
		child := types.child_type(expected, &checker.module.types)
		if types.equal(actual, child) ||
		   types.can_widen(actual, child) ||
		   types.can_weaken_pointer(actual, child, &checker.module.types) {
			value := coerce_expr(checker, expr_id, child, span)
			return add_hir_expr(checker, hir.Expr{
				kind=.Optional_Some,
				span=span,
				type=expected,
				left=value,
				target=hir.INVALID_REF,
				right=hir.INVALID_EXPR,
				diagnostic=source.INVALID_DIAGNOSTIC,
			})
		}
	}
	if types.can_widen(actual, expected) {
		return add_hir_expr(
			checker,
			hir.Expr {
				kind = .Widen,
				span = span,
				type = expected,
				left = expr_id,
				target = hir.INVALID_REF,
				right = hir.INVALID_EXPR,
				diagnostic = source.INVALID_DIAGNOSTIC,
			},
		)
	}
	id := source.addf(
		checker.diagnostics,
		span,
		"cannot implicitly convert %s to %s",
		types.name(actual),
		types.name(expected),
	)
	return invalid_hir_expr(checker, span, id, expected)
}

build_constant_expr :: proc(
	checker: ^Checker,
	expr: ast.Expr,
	constant: Constant,
	expected: types.Type,
) -> hir.Expr_Id {
	recovery_type := types.I64
	if types.is_concrete_integer(expected) {
		recovery_type = expected
	}
	if constant.kind == .Overflow ||
	   (!types.is_concrete_integer(expected) && !fits_i64(constant.value)) {
		id := source.add(
			checker.diagnostics,
			expr.span,
			"integer constant expression exceeds signed i64 range",
		)
		return invalid_hir_expr(checker, expr.span, id, recovery_type)
	}

	value := i64(constant.value)
	if constant.value >= 0 && constant.value <= i128(0xffff_ffff_ffff_ffff) {
		value = transmute(i64)u64(constant.value)
	}
	result_type := types.smallest_signed_for_literal(value)
	if types.is_concrete_integer(expected) {
		if !fits_integer_type(constant.value, expected, checker.target) {
			id := source.addf(
				checker.diagnostics,
				expr.span,
				"integer constant %d does not fit in %s",
				constant.value,
				types.name(expected),
			)
			return invalid_hir_expr(checker, expr.span, id, expected)
		}
		result_type = expected
	}
	return add_hir_expr(
		checker,
		hir.Expr {
			kind = .Integer,
			span = expr.span,
			type = result_type,
			integer = value,
			target = hir.INVALID_REF,
			left = hir.INVALID_EXPR,
			right = hir.INVALID_EXPR,
			diagnostic = source.INVALID_DIAGNOSTIC,
		},
	)
}

build_float_expr :: proc(checker: ^Checker, expr: ast.Expr, expected: types.Type) -> hir.Expr_Id {
	result_type := types.F64
	if types.is_float(expected, checker.target) {
		result_type = expected
	} else if types.is_valid(expected) {
		id := source.addf(
			checker.diagnostics,
			expr.span,
			"cannot implicitly convert f64 to %s",
			types.name(expected),
		)
		return invalid_hir_expr(checker, expr.span, id, expected)
	}
	value := transmute(f64)expr.integer
	bits := transmute(i64)value
	if types.bits(result_type, checker.target) == 32 {
		bits = i64(transmute(u32)f32(value))
	}
	return add_hir_expr(checker, hir.Expr{
		kind=.Float,
		span=expr.span,
		type=result_type,
		integer=bits,
		target=hir.INVALID_REF,
		left=hir.INVALID_EXPR,
		right=hir.INVALID_EXPR,
		diagnostic=source.INVALID_DIAGNOSTIC,
	})
}

Build_Expr_Frame :: struct {
	expr:       ast.Expr_Id,
	expected:   types.Type,
	stage:      u8,
	left:       hir.Expr_Id,
	arg_index:  int,
	built_args: []hir.Expr_Id,
	arg_types:  []types.Type,
	template:   ast.Function_Id,
}

hir_location_writable :: proc(checker: ^Checker, expr_id: hir.Expr_Id, locals: []Build_Local) -> bool {
	if expr_id == hir.INVALID_EXPR || int(expr_id) >= len(checker.module.exprs) {
		return false
	}
	expr := checker.module.exprs[expr_id]
	#partial switch expr.kind {
	case .Local:
		id := hir.as_local(expr.target)
		for local in locals {
			if local.id == id {
				return local.mutable
			}
		}
	case .Deref:
		pointer_type := checker.module.exprs[expr.left].type
		return types.is_mutable(pointer_type, &checker.module.types)
	case .Index:
		container_type := checker.module.exprs[expr.left].type
		return types.is_mutable(container_type, &checker.module.types)
	case .Field:
		base_type := checker.module.exprs[expr.left].type
		if types.is_pointer(base_type, &checker.module.types) {
			return types.is_mutable(base_type, &checker.module.types)
		}
		return hir_location_writable(checker, expr.left, locals)
	case:
	}
	return false
}

hir_is_location :: proc(checker: ^Checker, expr_id: hir.Expr_Id) -> bool {
	if expr_id == hir.INVALID_EXPR || int(expr_id) >= len(checker.module.exprs) {
		return false
	}
	#partial switch checker.module.exprs[expr_id].kind {
	case .Local, .Global, .Deref, .Index, .Field:
		return true
	}
	return false
}

find_struct_field :: proc(checker: ^Checker, struct_type: types.Type, name: symbol.Id) -> (int, types.Field, bool) {
	for field, index in types.fields_for(&checker.module.types, struct_type) {
		if field.name == u32(name) {
			return index, field, true
		}
	}
	return 0, {}, false
}

build_nested_expr :: proc(
	checker: ^Checker,
	expr_id: ast.Expr_Id,
	locals: []Build_Local,
	global_reads: ^[dynamic]hir.Global_Id,
	calls: ^[dynamic]hir.Function_Id,
	expected: types.Type,
	pkg: ast.Package_Id,
	file: ast.File_Id,
) -> hir.Expr_Id {
	outer := checker.build_stack
	checker.build_stack = nil
	checker.build_stack.allocator = checker.allocator
	result := build_expr(checker, expr_id, locals, global_reads, calls, expected, pkg, file)
	delete(checker.build_stack)
	checker.build_stack = outer
	return result
}

build_compound_expr :: proc(
	checker: ^Checker,
	expr: ast.Expr,
	locals: []Build_Local,
	global_reads: ^[dynamic]hir.Global_Id,
	calls: ^[dynamic]hir.Function_Id,
	expected: types.Type,
	pkg: ast.Package_Id,
	file: ast.File_Id,
) -> hir.Expr_Id {
	store := &checker.module.types
	#partial switch expr.kind {
	case .String:
		string_type := types.slice(store, types.U8, false, true, 0)
		return add_hir_expr(checker, hir.Expr{
			kind=.String, span=expr.span, type=string_type, integer=i64(expr.integer),
			target=hir.INVALID_REF, left=hir.INVALID_EXPR, right=hir.INVALID_EXPR,
			diagnostic=source.INVALID_DIAGNOSTIC,
		})
	case .Array:
		element_type := types.INVALID
		result_type := expected
		expected_node, has_expected := types.node(store, expected)
		if !has_expected || expected_node.kind != .Array {
			has_expected = false
			result_type = types.INVALID
		} else {
			element_type = expected_node.child
			if !expected_node.inferred_count && expected_node.count != u64(len(expr.args)) {
				id := source.addf(
					checker.diagnostics, expr.span,
					"array literal expects %d elements, got %d",
					expected_node.count, len(expr.args),
				)
				return invalid_hir_expr(checker, expr.span, id, expected)
			}
			if expected_node.inferred_count {
				result_type = types.with_array_count(store, expected, u64(len(expr.args)))
			}
		}
		if !has_expected {
			infer_locals := make([]Infer_Local, len(locals), checker.allocator)
			defer delete(infer_locals, checker.allocator)
			for local, index in locals {
				infer_locals[index] = Infer_Local{name=local.name, type=local.type}
			}
			for arg in expr.args {
				actual := infer_nested_expr(checker, arg, infer_locals, pkg, file, nil)
				if !types.is_valid(element_type) {
					element_type = actual
				} else {
					element_type = types.widest(element_type, actual)
				}
			}
			if !types.is_valid(element_type) {
				element_type = types.I64
			}
			result_type = types.array(store, element_type, u64(len(expr.args)), false)
		}
		args := make([]hir.Expr_Id, len(expr.args), checker.allocator)
		for arg, index in expr.args {
			args[index] = build_nested_expr(
				checker, arg, locals, global_reads, calls, element_type, pkg, file,
			)
			args[index] = coerce_expr(checker, args[index], element_type, checker.module.exprs[args[index]].span)
		}
		return add_hir_expr(checker, hir.Expr{
			kind=.Array, span=expr.span, type=result_type, args=args,
			target=hir.INVALID_REF, left=hir.INVALID_EXPR, right=hir.INVALID_EXPR,
			diagnostic=source.INVALID_DIAGNOSTIC,
		})
	case .None:
		if !types.is_optional(expected, store) {
			id := source.add(checker.diagnostics, expr.span, "'none' requires an optional context")
			return invalid_hir_expr(checker, expr.span, id, expected)
		}
		return add_hir_expr(checker, hir.Expr{
			kind=.None, span=expr.span, type=expected, target=hir.INVALID_REF,
			left=hir.INVALID_EXPR, right=hir.INVALID_EXPR, diagnostic=source.INVALID_DIAGNOSTIC,
		})
	case .Address:
		value := build_nested_expr(checker, expr.left, locals, global_reads, calls, types.INVALID, pkg, file)
		if !hir_is_location(checker, value) {
			id := source.add(checker.diagnostics, expr.span, "'&' requires an addressable location")
			return invalid_hir_expr(checker, expr.span, id)
		}
		value_type := checker.module.exprs[value].type
		writable := hir_location_writable(checker, value, locals)
		result_type := types.pointer(store, value_type, writable, false)
		if types.is_pointer(expected, store) &&
		   types.equal(types.child_type(expected, store), value_type) &&
		   (!types.is_mutable(expected, store) || writable) {
			result_type = expected
		}
		return add_hir_expr(checker, hir.Expr{
			kind=.Address, span=expr.span, type=result_type, left=value,
			target=hir.INVALID_REF, right=hir.INVALID_EXPR, diagnostic=source.INVALID_DIAGNOSTIC,
		})
	case .Deref:
		pointer := build_nested_expr(checker, expr.left, locals, global_reads, calls, types.INVALID, pkg, file)
		pointer_type := checker.module.exprs[pointer].type
		if !types.is_pointer(pointer_type, store) {
			id := source.add(checker.diagnostics, expr.span, "postfix '^' requires a pointer")
			return invalid_hir_expr(checker, expr.span, id)
		}
		return add_hir_expr(checker, hir.Expr{
			kind=.Deref, span=expr.span, type=types.child_type(pointer_type, store), left=pointer,
			target=hir.INVALID_REF, right=hir.INVALID_EXPR, diagnostic=source.INVALID_DIAGNOSTIC,
		})
	case .Index:
		container := build_nested_expr(checker, expr.left, locals, global_reads, calls, types.INVALID, pkg, file)
		index := build_nested_expr(checker, expr.right, locals, global_reads, calls, types.USIZE, pkg, file)
		container_type := checker.module.exprs[container].type
		item, ok := types.node(store, container_type)
		if !ok || (item.kind != .Array && item.kind != .Slice && !(item.kind == .Pointer && item.many)) {
			id := source.add(checker.diagnostics, expr.span, "indexing requires an array, slice, or many-item pointer")
			return invalid_hir_expr(checker, expr.span, id)
		}
		return add_hir_expr(checker, hir.Expr{
			kind=.Index, span=expr.span, type=item.child, left=container, right=index,
			target=hir.INVALID_REF, diagnostic=source.INVALID_DIAGNOSTIC,
		})
	case .Slice:
		container := build_nested_expr(checker, expr.left, locals, global_reads, calls, types.INVALID, pkg, file)
		container_type := checker.module.exprs[container].type
		item, ok := types.node(store, container_type)
		if !ok || (item.kind != .Array && item.kind != .Slice) {
			id := source.add(checker.diagnostics, expr.span, "slicing requires an array or slice")
			return invalid_hir_expr(checker, expr.span, id)
		}
		bounds := make([]hir.Expr_Id, 2, checker.allocator)
		bounds[0] = hir.INVALID_EXPR
		bounds[1] = hir.INVALID_EXPR
		for bound, index in expr.args {
			if bound != ast.INVALID_EXPR {
				bounds[index] = build_nested_expr(checker, bound, locals, global_reads, calls, types.USIZE, pkg, file)
			}
		}
		preserve_sentinel := item.has_sentinel && expr.args[1] == ast.INVALID_EXPR
		result_type := types.slice(store, item.child, item.mutable, preserve_sentinel, item.sentinel)
		return add_hir_expr(checker, hir.Expr{
			kind=.Slice, span=expr.span, type=result_type, args=bounds, left=container,
			target=hir.INVALID_REF, right=hir.INVALID_EXPR, diagnostic=source.INVALID_DIAGNOSTIC,
		})
	case .Field:
		base := build_nested_expr(checker, expr.left, locals, global_reads, calls, types.INVALID, pkg, file)
		base_type := checker.module.exprs[base].type
		item, has_item := types.node(store, base_type)
		field_name := symbol_text(checker, expr.name)
		if has_item && (item.kind == .Array || item.kind == .Slice) {
			if field_name == "len" {
				return add_hir_expr(checker, hir.Expr{
					kind=.Length, span=expr.span, type=types.USIZE, left=base,
					target=hir.INVALID_REF, right=hir.INVALID_EXPR, diagnostic=source.INVALID_DIAGNOSTIC,
				})
			}
			if field_name == "ptr" {
				return add_hir_expr(checker, hir.Expr{
					kind=.Slice_Ptr, span=expr.span,
					type=types.pointer(store, item.child, item.mutable, true), left=base,
					target=hir.INVALID_REF, right=hir.INVALID_EXPR, diagnostic=source.INVALID_DIAGNOSTIC,
				})
			}
		}
		if types.is_pointer(base_type, store) {
			base_type = types.child_type(base_type, store)
		}
		index, field, ok := find_struct_field(checker, base_type, expr.name)
		if !ok {
			id := source.addf(checker.diagnostics, expr.span, "unknown struct field '%s'", symbol_text(checker, expr.name))
			return invalid_hir_expr(checker, expr.span, id)
		}
		return add_hir_expr(checker, hir.Expr{
			kind=.Field, span=expr.span, type=field.type, integer=i64(index), left=base,
			target=hir.INVALID_REF, right=hir.INVALID_EXPR, diagnostic=source.INVALID_DIAGNOSTIC,
		})
	case .Unwrap:
		optional := build_nested_expr(checker, expr.left, locals, global_reads, calls, types.INVALID, pkg, file)
		optional_type := checker.module.exprs[optional].type
		if !types.is_optional(optional_type, store) {
			id := source.add(checker.diagnostics, expr.span, "postfix '?' requires an optional")
			return invalid_hir_expr(checker, expr.span, id)
		}
		return add_hir_expr(checker, hir.Expr{
			kind=.Unwrap, span=expr.span, type=types.child_type(optional_type, store), left=optional,
			target=hir.INVALID_REF, right=hir.INVALID_EXPR, diagnostic=source.INVALID_DIAGNOSTIC,
		})
	case .Orelse:
		optional := build_nested_expr(checker, expr.left, locals, global_reads, calls, types.INVALID, pkg, file)
		optional_type := checker.module.exprs[optional].type
		if !types.is_optional(optional_type, store) {
			id := source.add(checker.diagnostics, expr.span, "'orelse' requires an optional left operand")
			return invalid_hir_expr(checker, expr.span, id)
		}
		child := types.child_type(optional_type, store)
		fallback := build_nested_expr(checker, expr.right, locals, global_reads, calls, child, pkg, file)
		fallback = coerce_expr(checker, fallback, child, checker.module.exprs[fallback].span)
		return add_hir_expr(checker, hir.Expr{
			kind=.Orelse, span=expr.span, type=child, left=optional, right=fallback,
			target=hir.INVALID_REF, diagnostic=source.INVALID_DIAGNOSTIC,
		})
	case .Struct_Literal:
		target_pkg, available := expr_package(checker, expr, pkg, file, true)
		struct_type := types.find_named(store, u32(target_pkg), u32(expr.name)) if available else types.INVALID
		if !types.is_struct(struct_type, store) || types.is_opaque_struct(struct_type, store) {
			id := source.addf(checker.diagnostics, expr.span, "unknown or opaque struct type '%s'", symbol_text(checker, expr.name))
			return invalid_hir_expr(checker, expr.span, id)
		}
		if types.is_c_struct(struct_type, store) {
			id := source.add(checker.diagnostics, expr.span, "c_struct values cannot be constructed by value")
			return invalid_hir_expr(checker, expr.span, id)
		}
		fields := types.fields_for(store, struct_type)
		values := make([]hir.Expr_Id, len(fields), checker.allocator)
		initialized := make([]bool, len(fields), checker.allocator)
		defer delete(initialized, checker.allocator)
		for &value in values {
			value = hir.INVALID_EXPR
		}
		for keyed in expr.args {
			keyed_expr := checker.ast_module.exprs[keyed]
			index, field, ok := find_struct_field(checker, struct_type, keyed_expr.name)
			if !ok {
				source.addf(checker.diagnostics, keyed_expr.span, "unknown struct field '%s'", symbol_text(checker, keyed_expr.name))
				continue
			}
			if initialized[index] {
				source.addf(checker.diagnostics, keyed_expr.span, "duplicate initializer for struct field '%s'", symbol_text(checker, keyed_expr.name))
				continue
			}
			initialized[index] = true
			values[index] = build_nested_expr(checker, keyed_expr.left, locals, global_reads, calls, field.type, pkg, file)
			values[index] = coerce_expr(checker, values[index], field.type, keyed_expr.span)
		}
		for field, index in fields {
			if values[index] == hir.INVALID_EXPR {
				id := source.addf(checker.diagnostics, expr.span, "missing initializer for struct field '%s'", symbol_text(checker, symbol.Id(field.name)))
				delete(values, checker.allocator)
				return invalid_hir_expr(checker, expr.span, id, struct_type)
			}
		}
		return add_hir_expr(checker, hir.Expr{
			kind=.Struct, span=expr.span, type=struct_type, args=values,
			target=hir.INVALID_REF, left=hir.INVALID_EXPR, right=hir.INVALID_EXPR,
			diagnostic=source.INVALID_DIAGNOSTIC,
		})
	case .Keyed:
		id := source.add(checker.diagnostics, expr.span, "keyed initializer is only valid inside a struct literal")
		return invalid_hir_expr(checker, expr.span, id)
	case:
		return invalid_hir_expr(checker, expr.span, expr.diagnostic)
	}
}

build_expr :: proc(
	checker: ^Checker,
	expr_id: ast.Expr_Id,
	locals: []Build_Local,
	global_reads: ^[dynamic]hir.Global_Id,
	calls: ^[dynamic]hir.Function_Id,
	expected := types.INVALID,
	pkg := ast.Package_Id(0),
	file := ast.File_Id(0),
) -> hir.Expr_Id {
	stack := checker.build_stack
	clear_dynamic_array(&stack)
	defer {
		for frame in stack {
			delete(frame.built_args, checker.allocator)
			delete(frame.arg_types, checker.allocator)
		}
		clear_dynamic_array(&stack)
		checker.build_stack = stack
	}
	append(&stack, Build_Expr_Frame{expr=expr_id, expected=expected, template=ast.INVALID_FUNCTION})
	last := hir.INVALID_EXPR

	for len(stack) > 0 {
		frame_index := len(stack)-1
		frame := stack[frame_index]
		if frame.expr == ast.INVALID_EXPR || int(frame.expr) >= len(checker.ast_module.exprs) {
			id := source.add(checker.diagnostics, source.Span{}, "missing expression")
			last = invalid_hir_expr(checker, source.Span{}, id)
			_ = pop(&stack)
			continue
		}
		expr := checker.ast_module.exprs[frame.expr]
		if frame.stage == 0 {
			constant := eval_constant(checker, frame.expr)
			if constant.kind == .Value || constant.kind == .Overflow {
				last = build_constant_expr(checker, expr, constant, frame.expected)
				_ = pop(&stack)
				continue
			}
			switch expr.kind {
			case .String, .Array, .None, .Address, .Deref, .Index, .Slice,
			     .Field, .Unwrap, .Orelse, .Struct_Literal, .Keyed:
				last = build_compound_expr(
					checker, expr, locals, global_reads, calls, frame.expected, pkg, file,
				)
				_ = pop(&stack)
			case .Invalid, .Integer:
				last = invalid_hir_expr(checker, expr.span, expr.diagnostic)
				_ = pop(&stack)
			case .Float:
				last = build_float_expr(checker, expr, frame.expected)
				_ = pop(&stack)
			case .Name:
				last = hir.INVALID_EXPR
				if !symbol.is_valid(expr.qualifier) {
					if local, ok := find_build_local(locals, expr.name); ok {
						last = add_hir_expr(checker, hir.Expr{
							kind=.Local, span=expr.span, type=local.type, target=hir.local_ref(local.id),
							left = hir.INVALID_EXPR, right = hir.INVALID_EXPR, diagnostic = source.INVALID_DIAGNOSTIC,
						})
					}
				} else if local, ok := find_build_local(locals, expr.qualifier); ok {
					base := add_hir_expr(checker, hir.Expr{
						kind=.Local, span=expr.span, type=local.type, target=hir.local_ref(local.id),
						left=hir.INVALID_EXPR, right=hir.INVALID_EXPR, diagnostic=source.INVALID_DIAGNOSTIC,
					})
					base_type := local.type
					item, has_item := types.node(&checker.module.types, base_type)
					field_name := symbol_text(checker, expr.name)
					if has_item && (item.kind == .Array || item.kind == .Slice) {
						if field_name == "len" {
							last = add_hir_expr(checker, hir.Expr{
								kind=.Length, span=expr.span, type=types.USIZE, left=base,
								target=hir.INVALID_REF, right=hir.INVALID_EXPR, diagnostic=source.INVALID_DIAGNOSTIC,
							})
						} else if field_name == "ptr" {
							last = add_hir_expr(checker, hir.Expr{
								kind=.Slice_Ptr, span=expr.span,
								type=types.pointer(&checker.module.types, item.child, item.mutable, true), left=base,
								target=hir.INVALID_REF, right=hir.INVALID_EXPR, diagnostic=source.INVALID_DIAGNOSTIC,
							})
						}
					}
					if types.is_pointer(base_type, &checker.module.types) {
						base_type = types.child_type(base_type, &checker.module.types)
					}
					index, field, found := find_struct_field(checker, base_type, expr.name)
					if last == hir.INVALID_EXPR && found {
						last = add_hir_expr(checker, hir.Expr{
							kind=.Field, span=expr.span, type=field.type, integer=i64(index), left=base,
							target=hir.INVALID_REF, right=hir.INVALID_EXPR, diagnostic=source.INVALID_DIAGNOSTIC,
						})
					}
				}
				if last == hir.INVALID_EXPR {
					target_pkg, available := expr_package(checker, expr, pkg, file, true)
					if !available {
						id := add_package_resolution_diagnostic(checker, expr, file)
						last = invalid_hir_expr(checker, expr.span, id)
					} else if global := find_global(checker, expr.name, target_pkg); global != ast.INVALID_GLOBAL {
						hir_global := hir.Global_Id(global)
						add_unique_global(global_reads, hir_global)
						last = add_hir_expr(checker, hir.Expr{
							kind=.Global, span=expr.span, type=checker.global_types[global],
							target=hir.global_ref(hir_global), left = hir.INVALID_EXPR, right = hir.INVALID_EXPR, diagnostic = source.INVALID_DIAGNOSTIC,
						})
					} else {
						id := add_name_resolution_diagnostic(checker, expr, target_pkg)
						last = invalid_hir_expr(checker, expr.span, id)
					}
				}
				_ = pop(&stack)
			case .Negate:
				stack[frame_index].stage = 5
				append(&stack, Build_Expr_Frame{expr=expr.left, expected=types.INVALID, template=ast.INVALID_FUNCTION})
			case .Add:
				stack[frame_index].stage = 1
				append(&stack, Build_Expr_Frame{expr=expr.left, expected=types.INVALID, template=ast.INVALID_FUNCTION})
			case .Call:
				target_pkg, available := expr_package(checker, expr, pkg, file, true)
				if !available {
					id := add_package_resolution_diagnostic(checker, expr, file)
					last = invalid_hir_expr(checker, expr.span, id)
					_ = pop(&stack)
					continue
				}
				template := find_template(checker, expr.name, target_pkg)
				if template == ast.INVALID_FUNCTION {
					id := add_call_resolution_diagnostic(checker, expr, target_pkg)
					last = invalid_hir_expr(checker, expr.span, id)
					_ = pop(&stack)
					continue
				}
				if checker.template_diagnostics[template] != source.INVALID_DIAGNOSTIC {
					last = invalid_hir_expr(checker, expr.span, checker.template_diagnostics[template])
					_ = pop(&stack)
					continue
				}
				if len(expr.args) != len(checker.ast_module.functions[template].params) {
					id := source.addf(
						checker.diagnostics,
						expr.span,
						"function '%s' expects %d arguments, got %d",
						symbol_text(checker, expr.name),
						len(checker.ast_module.functions[template].params),
						len(expr.args),
					)
					last = invalid_hir_expr(checker, expr.span, id)
					_ = pop(&stack)
					continue
				}
				stack[frame_index].template = template
				stack[frame_index].built_args = make([]hir.Expr_Id, len(expr.args), checker.allocator)
				stack[frame_index].arg_types = make([]types.Type, len(expr.args), checker.allocator)
				stack[frame_index].stage = 3
				if len(expr.args) > 0 {
					arg_expected := type_from_syntax(checker.ast_module.functions[template].params[0].type)
					if !is_runtime_type(checker, arg_expected) {
						arg_expected = types.INVALID
					}
					append(&stack, Build_Expr_Frame{expr=expr.args[0], expected=arg_expected, template=ast.INVALID_FUNCTION})
				}
			}
			continue
		}
		if frame.stage == 5 {
			operand := last
			operand_type := checker.module.exprs[operand].type
			if !types.is_signed(operand_type, checker.target) && !types.is_float(operand_type, checker.target) {
				id := source.add(checker.diagnostics, expr.span, "negation requires a signed integer or float")
				last = invalid_hir_expr(checker, expr.span, id)
			} else {
				last = add_hir_expr(checker, hir.Expr{
					kind=.Negate, span=expr.span, type=operand_type, left=operand,
					target=hir.INVALID_REF, right=hir.INVALID_EXPR, diagnostic=source.INVALID_DIAGNOSTIC,
				})
				if types.is_signed(frame.expected, checker.target) || types.is_float(frame.expected, checker.target) {
					last = coerce_expr(checker, last, frame.expected, expr.span)
				}
			}
			_ = pop(&stack)
			continue
		}
		if frame.stage == 1 {
			stack[frame_index].left = last
			stack[frame_index].stage = 2
			right_expected := types.INVALID
			if types.is_many_pointer(checker.module.exprs[last].type, &checker.module.types) {
				right_expected = types.USIZE
			}
			append(&stack, Build_Expr_Frame{expr=expr.right, expected=right_expected, template=ast.INVALID_FUNCTION})
			continue
		}
		if frame.stage == 2 {
			left := frame.left
			right := last
			if types.is_many_pointer(checker.module.exprs[left].type, &checker.module.types) &&
			   types.equal(checker.module.exprs[right].type, types.USIZE) {
				last = add_hir_expr(checker, hir.Expr{
					kind=.Pointer_Add, span=expr.span, type=checker.module.exprs[left].type,
					left=left, right=right, target=hir.INVALID_REF, diagnostic=source.INVALID_DIAGNOSTIC,
				})
				_ = pop(&stack)
				continue
			}
			result := types.widest(checker.module.exprs[left].type, checker.module.exprs[right].type)
			if !types.is_concrete_scalar(result) {
				id := source.add(checker.diagnostics, expr.span, "addition requires compatible numeric operands")
				last = invalid_hir_expr(checker, expr.span, id)
			} else {
				left = coerce_expr(checker, left, result, checker.module.exprs[left].span)
				right = coerce_expr(checker, right, result, checker.module.exprs[right].span)
				last = add_hir_expr(checker, hir.Expr{
					kind=.Add, span=expr.span, type=result, left=left, right=right,
					target = hir.INVALID_REF, diagnostic = source.INVALID_DIAGNOSTIC,
				})
			}
			_ = pop(&stack)
			continue
		}
		if frame.stage == 3 {
			if frame.arg_index < len(expr.args) {
				stack[frame_index].built_args[frame.arg_index] = last
				stack[frame_index].arg_types[frame.arg_index] = checker.module.exprs[last].type
				stack[frame_index].arg_index += 1
				if frame.arg_index+1 < len(expr.args) {
					next := frame.arg_index+1
					arg_expected := type_from_syntax(checker.ast_module.functions[frame.template].params[next].type)
					if !is_runtime_type(checker, arg_expected) {
						arg_expected = types.INVALID
					}
					append(&stack, Build_Expr_Frame{expr=expr.args[next], expected=arg_expected, template=ast.INVALID_FUNCTION})
					continue
				}
			}
			spec := find_spec(checker, frame.template, stack[frame_index].arg_types)
			delete(stack[frame_index].arg_types, checker.allocator)
			stack[frame_index].arg_types = nil
			if spec == INVALID_SPEC {
				id := source.addf(
					checker.diagnostics,
					expr.span,
					"could not resolve specialization of '%s'",
					symbol_text(checker, expr.name),
				)
				delete(stack[frame_index].built_args, checker.allocator)
				stack[frame_index].built_args = nil
				last = invalid_hir_expr(checker, expr.span, id)
				_ = pop(&stack)
				continue
			}
			for _, index in stack[frame_index].built_args {
				stack[frame_index].built_args[index] = coerce_expr(
					checker,
					stack[frame_index].built_args[index],
					checker.specs[spec].args[index],
					checker.module.exprs[stack[frame_index].built_args[index]].span,
				)
			}
			function_id := checker.specs[spec].hir_id
			assert(function_id != hir.INVALID_FUNCTION)
			add_unique_function(calls, function_id)
			result := checker.specs[spec].result
			if !types.is_valid(result) {
				id := source.addf(
					checker.diagnostics,
					expr.span,
					"could not resolve result type for specialization of '%s'",
					symbol_text(checker, expr.name),
				)
				delete(stack[frame_index].built_args, checker.allocator)
				stack[frame_index].built_args = nil
				last = invalid_hir_expr(checker, expr.span, id)
			} else {
				last = add_hir_expr(checker, hir.Expr{
					kind=.Call, span=expr.span, type=result, target=hir.function_ref(function_id),
					left = hir.INVALID_EXPR, right = hir.INVALID_EXPR, args=stack[frame_index].built_args, diagnostic = source.INVALID_DIAGNOSTIC,
				})
				stack[frame_index].built_args = nil
			}
			_ = pop(&stack)
		}
	}
	return last
}

make_link_name :: proc(checker: ^Checker, id: Spec_Id) -> string {
	spec := checker.specs[id]
	function := checker.ast_module.functions[spec.template]
	if function.pkg == 0 && function.name == checker.main_symbol {
		return fmt.aprintf("main", allocator = checker.allocator)
	}
	if !function.has_body && function.c_abi {
		return fmt.aprintf("%s", symbol_text(checker, function.name), allocator = checker.allocator)
	}
	builder := strings.builder_make(checker.allocator)
	defer strings.builder_destroy(&builder)
	strings.write_string(&builder, "bro_c__" if function.c_abi else "bro__")
	fmt.sbprintf(&builder, "p%d__", function.pkg)
	strings.write_string(&builder, symbol_text(checker, function.name))
	for arg in spec.args {
		strings.write_string(&builder, "__")
		if arg >= types.DYNAMIC_START {
			fmt.sbprintf(&builder, "t%d", arg)
		} else {
			strings.write_string(&builder, types.name(arg))
		}
	}
	return fmt.aprintf("%s", strings.to_string(builder), allocator = checker.allocator)
}

build_function :: proc(checker: ^Checker, id: Spec_Id) {
	spec := checker.specs[id]
	function := checker.ast_module.functions[spec.template]
	signature_diagnostic := source.INVALID_DIAGNOSTIC
	if !types.is_void(spec.result) && !is_runtime_type(checker, spec.result) {
		checker.specs[id].result = types.I64
		spec.result = types.I64
		signature_diagnostic = source.addf(
			checker.diagnostics,
			function.span,
			"could not resolve a concrete result type for '%s'",
			symbol_text(checker, function.name),
		)
	}
	for arg in spec.args {
		if !is_runtime_type(checker, arg) {
			signature_diagnostic = source.addf(
				checker.diagnostics,
				function.span,
				"could not resolve a concrete parameter type for '%s'",
				symbol_text(checker, function.name),
			)
			break
		}
	}
	assert(spec.hir_id == hir.function_id(len(checker.module.functions)))

	locals: [dynamic]Build_Local
	locals.allocator = checker.allocator
	hir_locals: [dynamic]hir.Local
	hir_locals.allocator = checker.allocator
	params: [dynamic]hir.Local_Id
	params.allocator = checker.allocator
	body: [dynamic]hir.Stmt_Id
	body.allocator = checker.allocator
	global_reads: [dynamic]hir.Global_Id
	global_reads.allocator = checker.allocator
	calls: [dynamic]hir.Function_Id
	calls.allocator = checker.allocator

	for param, index in function.params {
		local_id := hir.local_id(len(hir_locals))
		param_type := types.INVALID
		if index < len(spec.args) {
			param_type = spec.args[index]
		}
		append(&hir_locals, hir.Local{name = param.name, type = param_type, parameter = true})
		append(&locals, Build_Local{name = param.name, type = param_type, id = local_id})
		append(&params, local_id)
	}

	problematic := signature_diagnostic != source.INVALID_DIAGNOSTIC ||
	               checker.template_diagnostics[spec.template] != source.INVALID_DIAGNOSTIC
	if !function.has_body {
		assert(spec.hir_id == hir.function_id(len(checker.module.functions)))
		append(
			&checker.module.functions,
			hir.Function {
				name = function.name,
				link_name = make_link_name(checker, id),
				calling_convention = .C if function.c_abi else .Brolang,
				implementation = .Declaration,
				linkage = .External if function.c_abi else .Internal,
				is_main = function.pkg == 0 && function.name == checker.main_symbol,
				params = params[:],
				result = spec.result,
				locals = hir_locals[:],
				body = body[:],
				direct_global_reads = global_reads,
				calls = calls[:],
				problematic = problematic,
				diagnostic = checker.template_diagnostics[spec.template],
			},
		)
		delete(locals)
		return
	}

	has_return := false
	if signature_diagnostic != source.INVALID_DIAGNOSTIC {
		append(&body, hir.stmt_id(len(checker.module.statements)))
		append(
			&checker.module.statements,
			hir.Stmt {
				kind = .Trap,
				span = function.span,
				expr = hir.INVALID_EXPR,
				local = hir.INVALID_LOCAL,
				diagnostic = signature_diagnostic,
			},
		)
	}
	for statement_id in function.body {
		statement := checker.ast_module.statements[statement_id]
		switch statement.kind {
		case .Declaration:
			declared := resolve_inferred_array(checker, type_from_syntax(statement.type), statement.expr)
			expected := types.INVALID
			if is_runtime_type(checker, declared) {
				expected = declared
			}
			value := build_expr(
				checker,
				statement.expr,
				locals[:],
				&global_reads,
				&calls,
				expected,
				function.pkg,
				function.file,
			)
			value_type := checker.module.exprs[value].type
			if is_runtime_type(checker, declared) {
				value = coerce_expr(checker, value, declared, statement.span)
				value_type = checker.module.exprs[value].type
			} else if types.is_void(declared) {
				id := source.add(
					checker.diagnostics,
					statement.span,
					"locals cannot have type void",
				)
				value = invalid_hir_expr(checker, statement.span, id)
				value_type = types.INVALID
			}
			if _, found := find_build_local(locals[:], statement.name); found {
				id := source.addf(
					checker.diagnostics,
					statement.span,
					"duplicate local '%s'",
					symbol_text(checker, statement.name),
				)
				append(&body, hir.stmt_id(len(checker.module.statements)))
				append(
					&checker.module.statements,
					hir.Stmt {
						kind = .Trap,
						span = statement.span,
						expr = hir.INVALID_EXPR,
						local = hir.INVALID_LOCAL,
						diagnostic = id,
					},
				)
				problematic = true
				continue
			}
			local_id := hir.local_id(len(hir_locals))
			append(
				&hir_locals,
				hir.Local {
					name = statement.name,
					type = value_type,
					mutable = !statement.immutable,
				},
			)
			append(
				&locals,
				Build_Local {
					name = statement.name,
					type = value_type,
					mutable = !statement.immutable,
					id = local_id,
				},
			)
			append(&body, hir.stmt_id(len(checker.module.statements)))
			append(
				&checker.module.statements,
				hir.Stmt {
					kind = .Declaration,
					span = statement.span,
					local = local_id,
					expr = value,
					diagnostic = source.INVALID_DIAGNOSTIC,
				},
			)
			problematic = problematic || checker.module.exprs[value].kind == .Invalid
		case .Assignment:
			if statement.target != ast.INVALID_EXPR {
				target_expr := build_expr(
					checker, statement.target, locals[:], &global_reads, &calls,
					types.INVALID, function.pkg, function.file,
				)
				target_type := checker.module.exprs[target_expr].type
				if !hir_location_writable(checker, target_expr, locals[:]) {
					id := source.add(checker.diagnostics, statement.span, "assignment target is not writable")
					append(&body, hir.stmt_id(len(checker.module.statements)))
					append(&checker.module.statements, hir.Stmt{
						kind=.Trap, span=statement.span, local=hir.INVALID_LOCAL,
						target=hir.INVALID_EXPR, expr=hir.INVALID_EXPR, diagnostic=id,
					})
					problematic = true
					continue
				}
				value := build_expr(
					checker, statement.expr, locals[:], &global_reads, &calls,
					target_type, function.pkg, function.file,
				)
				value = coerce_expr(checker, value, target_type, statement.span)
				append(&body, hir.stmt_id(len(checker.module.statements)))
				append(&checker.module.statements, hir.Stmt{
					kind=.Assignment, span=statement.span, local=hir.INVALID_LOCAL,
					target=target_expr, expr=value, diagnostic=source.INVALID_DIAGNOSTIC,
				})
				problematic = problematic || checker.module.exprs[value].kind == .Invalid
				continue
			}
			if statement.name == checker.sink_symbol {
				value := build_expr(checker, statement.expr, locals[:], &global_reads, &calls, types.INVALID, function.pkg, function.file)
				if types.is_void(checker.module.exprs[value].type) {
					id := source.add(
						checker.diagnostics,
						statement.span,
						"cannot assign a void expression to '_'",
					)
					append(&body, hir.stmt_id(len(checker.module.statements)))
					append(
						&checker.module.statements,
						hir.Stmt {
							kind = .Trap,
							span = statement.span,
							expr = hir.INVALID_EXPR,
							local = hir.INVALID_LOCAL,
							diagnostic = id,
						},
					)
					problematic = true
				} else {
					append(&body, hir.stmt_id(len(checker.module.statements)))
					append(
						&checker.module.statements,
						hir.Stmt {
							kind = .Sink,
							span = statement.span,
							expr = value,
							local = hir.INVALID_LOCAL,
							diagnostic = source.INVALID_DIAGNOSTIC,
						},
					)
				}
				continue
			}
			local, found := find_build_local(locals[:], statement.name)
			if !found {
				id := source.addf(
					checker.diagnostics,
					statement.span,
					"cannot assign unresolved local '%s'",
					symbol_text(checker, statement.name),
				)
				append(&body, hir.stmt_id(len(checker.module.statements)))
				append(
					&checker.module.statements,
					hir.Stmt {
						kind = .Trap,
						span = statement.span,
						expr = hir.INVALID_EXPR,
						local = hir.INVALID_LOCAL,
						diagnostic = id,
					},
				)
				problematic = true
				continue
			}
			if !local.mutable {
				id := source.addf(
					checker.diagnostics,
					statement.span,
					"cannot assign immutable local '%s'",
					symbol_text(checker, statement.name),
				)
				append(&body, hir.stmt_id(len(checker.module.statements)))
				append(
					&checker.module.statements,
					hir.Stmt {
						kind = .Trap,
						span = statement.span,
						expr = hir.INVALID_EXPR,
						local = hir.INVALID_LOCAL,
						diagnostic = id,
					},
				)
				problematic = true
				continue
			}
			value := build_expr(
				checker,
				statement.expr,
				locals[:],
				&global_reads,
				&calls,
				local.type,
				function.pkg,
				function.file,
			)
			value = coerce_expr(checker, value, local.type, statement.span)
			append(&body, hir.stmt_id(len(checker.module.statements)))
			append(
				&checker.module.statements,
				hir.Stmt {
					kind = .Assignment,
					span = statement.span,
					expr = value,
					local = local.id,
					target = hir.INVALID_EXPR,
					diagnostic = source.INVALID_DIAGNOSTIC,
				},
			)
			problematic = problematic || checker.module.exprs[value].kind == .Invalid
		case .Return:
			has_return = true
			if statement.expr == ast.INVALID_EXPR {
				if !types.is_void(spec.result) {
					id := source.add(
						checker.diagnostics,
						statement.span,
						"'return _' is only valid in a void function",
					)
					append(&body, hir.stmt_id(len(checker.module.statements)))
					append(
						&checker.module.statements,
						hir.Stmt {
							kind = .Trap,
							span = statement.span,
							expr = hir.INVALID_EXPR,
							local = hir.INVALID_LOCAL,
							diagnostic = id,
						},
					)
					problematic = true
				} else {
					append(&body, hir.stmt_id(len(checker.module.statements)))
					append(
						&checker.module.statements,
						hir.Stmt {
							kind = .Return,
							span = statement.span,
							expr = hir.INVALID_EXPR,
							local = hir.INVALID_LOCAL,
							diagnostic = source.INVALID_DIAGNOSTIC,
						},
					)
				}
				continue
			}
			if types.is_void(spec.result) {
				id := source.add(
					checker.diagnostics,
					statement.span,
					"void function cannot return a value",
				)
				append(&body, hir.stmt_id(len(checker.module.statements)))
				append(
					&checker.module.statements,
					hir.Stmt {
						kind = .Trap,
						span = statement.span,
						expr = hir.INVALID_EXPR,
						local = hir.INVALID_LOCAL,
						diagnostic = id,
					},
				)
				problematic = true
				continue
			}
			value := build_expr(
				checker,
				statement.expr,
				locals[:],
				&global_reads,
				&calls,
				spec.result,
				function.pkg,
				function.file,
			)
			value = coerce_expr(checker, value, spec.result, statement.span)
			append(&body, hir.stmt_id(len(checker.module.statements)))
			append(
				&checker.module.statements,
				hir.Stmt {
					kind = .Return,
					span = statement.span,
					expr = value,
					local = hir.INVALID_LOCAL,
					diagnostic = source.INVALID_DIAGNOSTIC,
				},
			)
			problematic = problematic || checker.module.exprs[value].kind == .Invalid
		case .Expression:
			value := build_expr(checker, statement.expr, locals[:], &global_reads, &calls, types.INVALID, function.pkg, function.file)
			if !types.is_void(checker.module.exprs[value].type) {
				id := source.add(
					checker.diagnostics,
					statement.span,
					"non-void expression result must be consumed or assigned to '_'",
				)
				append(&body, hir.stmt_id(len(checker.module.statements)))
				append(
					&checker.module.statements,
					hir.Stmt {
						kind = .Trap,
						span = statement.span,
						expr = hir.INVALID_EXPR,
						local = hir.INVALID_LOCAL,
						diagnostic = id,
					},
				)
				problematic = true
			} else {
				append(&body, hir.stmt_id(len(checker.module.statements)))
				append(
					&checker.module.statements,
					hir.Stmt {
						kind = .Expression,
						span = statement.span,
						expr = value,
						local = hir.INVALID_LOCAL,
						diagnostic = source.INVALID_DIAGNOSTIC,
					},
				)
			}
		case .Invalid:
			append(&body, hir.stmt_id(len(checker.module.statements)))
			append(
				&checker.module.statements,
				hir.Stmt {
					kind = .Trap,
					span = statement.span,
					expr = hir.INVALID_EXPR,
					local = hir.INVALID_LOCAL,
					diagnostic = statement.diagnostic,
				},
			)
			problematic = true
		}
	}

	if !types.is_void(spec.result) && !has_return {
		id := source.addf(
			checker.diagnostics,
			function.span,
			"function '%s' does not return a value",
			symbol_text(checker, function.name),
		)
		append(&body, hir.stmt_id(len(checker.module.statements)))
		append(
			&checker.module.statements,
			hir.Stmt{kind = .Trap, span = function.span, expr = hir.INVALID_EXPR, local = hir.INVALID_LOCAL, diagnostic = id},
		)
		problematic = true
	}

	assert(spec.hir_id == hir.function_id(len(checker.module.functions)))
	append(
		&checker.module.functions,
		hir.Function {
			name = function.name,
			link_name = make_link_name(checker, id),
			calling_convention = .C if function.c_abi || (function.pkg == 0 && function.name == checker.main_symbol) else .Brolang,
			implementation = .Definition,
			linkage = .External if function.c_abi || (function.pkg == 0 && function.name == checker.main_symbol) else .Internal,
			is_main = function.pkg == 0 && function.name == checker.main_symbol,
			params = params[:],
			result = spec.result,
			locals = hir_locals[:],
			body = body[:],
			direct_global_reads = global_reads,
			calls = calls[:],
			problematic = problematic,
			diagnostic = source.INVALID_DIAGNOSTIC,
		},
	)
	delete(locals)
}

expr_problematic :: proc(checker: ^Checker, expr_id: hir.Expr_Id) -> bool {
	module := &checker.module
	stack := checker.hir_expr_stack
	clear_dynamic_array(&stack)
	defer {
		clear_dynamic_array(&stack)
		checker.hir_expr_stack = stack
	}
	append(&stack, expr_id)
	for len(stack) > 0 {
		id := pop(&stack)
		if id == hir.INVALID_EXPR || int(id) >= len(module.exprs) {
			return true
		}
		expr := module.exprs[id]
		if expr.kind == .Invalid {
			return true
		}
		if expr.left != hir.INVALID_EXPR {
			append(&stack, expr.left)
		}
		if expr.right != hir.INVALID_EXPR {
			append(&stack, expr.right)
		}
		append(&stack, ..expr.args)
	}
	return false
}

build_globals :: proc(checker: ^Checker) {
	for global, global_index in checker.ast_module.globals {
		dependencies: [dynamic]hir.Global_Id
		dependencies.allocator = checker.allocator
		calls: [dynamic]hir.Function_Id
		calls.allocator = checker.allocator
		declared := resolve_inferred_array(checker, type_from_syntax(global.type), global.expr)
		expected := types.INVALID
		if is_runtime_type(checker, declared) {
			expected = declared
		}
		expr := build_expr(checker, global.expr, nil, &dependencies, &calls, expected, global.pkg, global.file)
		global_type := checker.global_types[global_index]
		if is_runtime_type(checker, declared) {
			expr = coerce_expr(checker, expr, declared, global.span)
			global_type = checker.module.exprs[expr].type
		} else if is_runtime_type(checker, checker.module.exprs[expr].type) {
			global_type = checker.module.exprs[expr].type
		}
		diagnostic := source.INVALID_DIAGNOSTIC
		if !is_runtime_type(checker, global_type) {
			diagnostic = source.addf(
				checker.diagnostics,
				global.span,
				"could not resolve a concrete type for global '%s'",
				symbol_text(checker, global.name),
			)
			global_type = types.I64
			expr = invalid_hir_expr(checker, global.span, diagnostic, global_type)
		}
		if global.type == types.VOID {
			diagnostic = source.add(
				checker.diagnostics,
				global.span,
				"void is only valid as a function result type",
			)
			expr = invalid_hir_expr(checker, global.span, diagnostic)
		}
		if !global.immutable {
			diagnostic = source.add(
				checker.diagnostics,
				global.span,
				"mutable declarations are only valid inside functions",
			)
			expr = invalid_hir_expr(checker, global.span, diagnostic)
		}
		is_static := checker.module.exprs[expr].kind == .Integer && diagnostic == source.INVALID_DIAGNOSTIC
		static_value: i64
		if is_static {
			static_value = checker.module.exprs[expr].integer
		}
		_ = hir.global_id(len(checker.module.globals))
		append(
			&checker.module.globals,
			hir.Global {
				name = global.name,
				type = global_type,
				expr = expr,
				static_value = static_value,
				is_static = is_static,
				dependencies = dependencies,
				calls = calls[:],
				direct_problem = expr_problematic(checker, expr),
				problematic = expr_problematic(checker, expr),
				diagnostic = diagnostic,
			},
		)
	}
}

propagate_problems :: proc(checker: ^Checker) {
	changed := true
	for changed {
		changed = false
		for &function in checker.module.functions {
			if function.problematic {
				continue
			}
			for call in function.calls {
				if call != hir.INVALID_FUNCTION && int(call) < len(checker.module.functions) &&
				   checker.module.functions[call].problematic {
					function.problematic = true
					changed = true
					break
				}
			}
		}
		for &global in checker.module.globals {
			if global.problematic {
				continue
			}
			for dependency in global.dependencies {
				if dependency != hir.INVALID_GLOBAL &&
				   int(dependency) < len(checker.module.globals) &&
				   checker.module.globals[dependency].problematic {
					global.problematic = true
					changed = true
					break
				}
			}
			if global.problematic {
				continue
			}
			for call in global.calls {
				if call != hir.INVALID_FUNCTION && int(call) < len(checker.module.functions) &&
				   checker.module.functions[call].problematic {
					global.problematic = true
					changed = true
					break
				}
			}
		}
	}
}

append_unique_global :: proc(values: ^[dynamic]hir.Global_Id, value: hir.Global_Id) -> bool {
	for existing in values^ {
		if existing == value {
			return false
		}
	}
	append(values, value)
	return true
}

propagate_global_reads :: proc(checker: ^Checker) {
	changed := true
	for changed {
		changed = false
		for &function in checker.module.functions {
			for call in function.calls {
				if call == hir.INVALID_FUNCTION || int(call) >= len(checker.module.functions) {
					continue
				}
				for global_id in checker.module.functions[call].direct_global_reads {
					if append_unique_global(&function.direct_global_reads, global_id) {
						changed = true
					}
				}
			}
		}
	}
	for &global in checker.module.globals {
		for call in global.calls {
			if call == hir.INVALID_FUNCTION || int(call) >= len(checker.module.functions) {
				continue
			}
			for dependency in checker.module.functions[call].direct_global_reads {
				_ = append_unique_global(&global.dependencies, dependency)
			}
		}
	}
}

Cycle_Frame :: struct {
	global:          hir.Global_Id,
	next_dependency: int,
}

detect_global_cycles_visit :: proc(checker: ^Checker, global_id: hir.Global_Id, states: []u8) {
	if states[global_id] == 2 {
		return
	}
	stack := checker.cycle_stack
	clear_dynamic_array(&stack)
	defer {
		clear_dynamic_array(&stack)
		checker.cycle_stack = stack
	}
	append(&stack, Cycle_Frame{global=global_id})
	for len(stack) > 0 {
		frame_index := len(stack)-1
		frame := &stack[frame_index]
		if states[frame.global] == 0 {
			states[frame.global] = 1
		}
		dependencies := checker.module.globals[frame.global].dependencies
		if frame.next_dependency >= len(dependencies) {
			states[frame.global] = 2
			if checker.module.globals[frame.global].problematic && frame_index > 0 {
				checker.module.globals[stack[frame_index-1].global].problematic = true
			}
			_ = pop(&stack)
			continue
		}
		dependency := dependencies[frame.next_dependency]
		frame.next_dependency += 1
		if dependency == hir.INVALID_GLOBAL || int(dependency) >= len(states) {
			continue
		}
		if states[dependency] == 1 {
			id := source.addf(
				checker.diagnostics,
				checker.ast_module.globals[dependency].span,
				"global initialization cycle involving '%s'",
				symbol_text(checker, checker.module.globals[dependency].name),
			)
			checker.module.globals[dependency].diagnostic = id
			checker.module.globals[dependency].problematic = true
			checker.module.globals[frame.global].problematic = true
			continue
		}
		if states[dependency] == 2 {
			if checker.module.globals[dependency].problematic {
				checker.module.globals[frame.global].problematic = true
			}
			continue
		}
		append(&stack, Cycle_Frame{global=dependency})
	}
}

synthesize_trap_main :: proc(checker: ^Checker) {
	id := source.add(checker.diagnostics, source.Span{}, "missing or unusable main function")
	statement_id := hir.stmt_id(len(checker.module.statements))
	_ = hir.function_id(len(checker.module.functions))
	append(
		&checker.module.statements,
		hir.Stmt{kind = .Trap, span = source.Span{}, expr = hir.INVALID_EXPR, local = hir.INVALID_LOCAL, diagnostic = id},
	)
	body := make([]hir.Stmt_Id, 1, checker.allocator)
	body[0] = statement_id
	append(
		&checker.module.functions,
		hir.Function {
			name = checker.main_symbol,
			link_name = fmt.aprintf("main", allocator = checker.allocator),
			calling_convention = .C,
			implementation = .Definition,
			linkage = .External,
			is_main = true,
			result = types.VOID,
			body = body,
			problematic = true,
			diagnostic = id,
		},
	)
}

replace_main_with_trap :: proc(checker: ^Checker, diagnostic: source.Diagnostic_Id) {
	for &function in checker.module.functions {
		if !function.is_main {
			continue
		}
		delete(function.params, checker.allocator)
		delete(function.body, checker.allocator)
		function.params = nil
		function.result = types.VOID
		function.calling_convention = .C
		function.implementation = .Definition
		function.linkage = .External
		function.problematic = true
		function.diagnostic = diagnostic
		statement_id := hir.stmt_id(len(checker.module.statements))
		append(
			&checker.module.statements,
			hir.Stmt {
				kind = .Trap,
				span = source.Span{},
				expr = hir.INVALID_EXPR,
				local = hir.INVALID_LOCAL,
				diagnostic = diagnostic,
			},
		)
		function.body = make([]hir.Stmt_Id, 1, checker.allocator)
		function.body[0] = statement_id
		return
	}
	synthesize_trap_main(checker)
}

check :: proc(
	ast_module: ^ast.Module,
	diagnostics: ^source.Diagnostics,
	symbols: ^symbol.Table,
	selected := target.DEFAULT,
	allocator := context.allocator,
) -> hir.Module {
	checker := Checker {
		ast_module  = ast_module,
		diagnostics = diagnostics,
		symbols     = symbols,
		module      = hir.init_module(selected, allocator),
		main_symbol = symbol.intern(symbols, "main"),
		sink_symbol = symbol.intern(symbols, "_"),
		target      = selected,
		allocator   = allocator,
	}
	checker.specs.allocator = allocator
	types.destroy_store(&checker.module.types)
	checker.module.types = types.clone_store(&ast_module.type_store, allocator)
	checker.module.types.selected = selected
	for value in ast_module.strings {
		append(&checker.module.strings, strings.clone(value, allocator))
	}
	checker.constant_stack.allocator = allocator
	checker.ast_expr_stack.allocator = allocator
	checker.hir_expr_stack.allocator = allocator
	checker.infer_stack.allocator = allocator
	checker.build_stack.allocator = allocator
	checker.cycle_stack.allocator = allocator
	build_symbol_indexes(&checker)
	checker.global_types = make([]types.Type, len(ast_module.globals), allocator)
	checker.constants = make([]Constant, len(ast_module.exprs), allocator)
	checker.template_diagnostics = make([]source.Diagnostic_Id, len(ast_module.functions), allocator)
	for &diagnostic in checker.template_diagnostics {
		diagnostic = source.INVALID_DIAGNOSTIC
	}
	defer {
		for spec in checker.specs {
			delete(spec.args, allocator)
		}
		delete(checker.specs)
		delete(checker.function_index, allocator)
		delete(checker.global_index, allocator)
		delete(checker.import_index, allocator)
		delete(checker.global_types, allocator)
		delete(checker.constants, allocator)
		delete(checker.template_diagnostics, allocator)
		delete(checker.constant_stack)
		delete(checker.ast_expr_stack)
		delete(checker.hir_expr_stack)
		delete(checker.infer_stack)
		delete(checker.build_stack)
		delete(checker.cycle_stack)
	}

	for function, index in ast_module.functions {
		for previous in ast_module.functions[:index] {
			if previous.pkg == function.pkg && previous.name == function.name {
				source.addf(diagnostics, function.span, "duplicate function '%s'", symbol_text(&checker, function.name))
			}
		}
		for global in ast_module.globals {
			if global.pkg == function.pkg && global.name == function.name {
				source.addf(diagnostics, function.span, "package declaration '%s' conflicts with a global", symbol_text(&checker, function.name))
			}
		}
	}
	for global, index in ast_module.globals {
		for previous in ast_module.globals[:index] {
			if previous.pkg == global.pkg && previous.name == global.name {
				source.addf(diagnostics, global.span, "duplicate global '%s'", symbol_text(&checker, global.name))
			}
		}
	}

	validate_type_nodes(&checker)
	validate_declarations(&checker)
	infer_all(&checker)
	prune_specs(&checker)
	build_globals(&checker)
	for index := 0; index < len(checker.specs); index += 1 {
		build_function(&checker, spec_id(index))
	}
	propagate_global_reads(&checker)

	main_template := find_template(&checker, checker.main_symbol, 0)
	main_declarations := 0
	for function in ast_module.functions {
		if function.pkg == 0 && function.name == checker.main_symbol {
			main_declarations += 1
		}
	}
	if main_declarations == 0 {
		synthesize_trap_main(&checker)
	} else {
		template := ast_module.functions[main_template]
		if main_declarations != 1 ||
		   !template.has_body ||
		   len(template.params) != 0 ||
		   !(template.result == types.VOID || template.result == types.I32 || template.result == types.INT) {
			id := checker.template_diagnostics[main_template]
			if id == source.INVALID_DIAGNOSTIC {
				id = source.add(
					diagnostics,
					template.span,
					"main must be unique, have a body, take no parameters, and return void, i32, or int",
				)
			}
			replace_main_with_trap(&checker, id)
		}
	}

	propagate_problems(&checker)
	states := make([]u8, len(checker.module.globals), allocator)
	for index in 0 ..< len(checker.module.globals) {
		detect_global_cycles_visit(&checker, hir.global_id(index), states)
	}
	delete(states, allocator)
	propagate_problems(&checker)
	for import_item in ast_module.imports {
		if import_item.valid && !import_item.used {
			source.addf(diagnostics, import_item.span, "unused import '%s'", symbol_text(&checker, import_item.alias))
		}
	}
	return checker.module
}