brolang/compiler/checker/checker.odin

package checker

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

Spec :: struct {
	template: int,
	args:     []types.Type,
	result:   types.Type,
	hir_id:   int,
}

Infer_Local :: struct {
	name: string,
	type: types.Type,
}

Build_Local :: struct {
	name:    string,
	type:    types.Type,
	mutable: bool,
	id:      int,
}

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

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

Symbol_Index_Entry :: struct {
	scope: int,
	name:  string,
	id:    int,
}

Checker :: struct {
	ast_module:     ^ast.Module,
	diagnostics:    ^source.Diagnostics,
	module:         hir.Module,
	specs:          [dynamic]Spec,
	function_index: []Symbol_Index_Entry,
	global_index:   []Symbol_Index_Entry,
	import_index:   []Symbol_Index_Entry,
	global_types:   []types.Type,
	constants:      []Constant,
	allocator:      mem.Allocator,
}

eval_constant :: proc(checker: ^Checker, expr_id: int) -> Constant {
	if expr_id < 0 || expr_id >= len(checker.ast_module.exprs) {
		return Constant{kind = .Not_Constant}
	}
	if checker.constants[expr_id].kind != .Unknown {
		return checker.constants[expr_id]
	}
	expr := checker.ast_module.exprs[expr_id]
	result: Constant
	switch expr.kind {
	case .Integer:
		result = Constant{kind = .Value, value = i128(expr.integer)}
	case .Add:
		left := eval_constant(checker, expr.left)
		right := eval_constant(checker, expr.right)
		if left.kind == .Overflow || right.kind == .Overflow {
			result = Constant{kind = .Overflow}
		} else if left.kind != .Value || right.kind != .Value {
			result = Constant{kind = .Not_Constant}
		} else {
			value, overflow := intrinsics.overflow_add(left.value, right.value)
			if overflow {
				result = Constant{kind = .Overflow}
			} else {
				result = Constant{kind = .Value, value = value}
			}
		}
	case .Invalid, .Name, .Call:
		result = Constant{kind = .Not_Constant}
	}
	checker.constants[expr_id] = result
	return result
}

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

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

type_from_syntax :: proc(value: ast.Type_Syntax) -> types.Type {
	switch value {
	case .Int:
		return types.INT
	case .I8:
		return types.I8
	case .I16:
		return types.I16
	case .I32:
		return types.I32
	case .I64:
		return types.I64
	case .Void:
		return types.VOID
	case .Invalid:
		return types.INVALID
	}
	return types.INVALID
}

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

find_symbol :: proc(index: []Symbol_Index_Entry, scope: int, name: string) -> int {
	low := 0
	high := len(index)
	for low < high {
		middle := low + (high-low)/2
		entry := index[middle]
		if entry.scope < scope || entry.scope == scope && entry.name < name {
			low = middle + 1
		} else {
			high = middle
		}
	}
	if low < len(index) && index[low].scope == scope && index[low].name == name {
		return index[low].id
	}
	return -1
}

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

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

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

find_template :: proc(checker: ^Checker, name: string, pkg := 0) -> int {
	return find_symbol(checker.function_index, pkg, name)
}

find_global :: proc(checker: ^Checker, name: string, pkg := 0) -> int {
	return find_symbol(checker.global_index, pkg, name)
}

find_import :: proc(checker: ^Checker, file: int, alias: string, mark_used := false) -> int {
	id := find_symbol(checker.import_index, file, alias)
	if id >= 0 && mark_used {
		checker.ast_module.imports[id].used = true
	}
	return id
}

expr_package :: proc(checker: ^Checker, expr: ast.Expr, pkg, file: int, mark_used := false) -> (int, bool) {
	if expr.qualifier == "" {
		return pkg, true
	}
	import_id := find_import(checker, file, expr.qualifier, mark_used)
	if import_id < 0 {
		return -1, false
	}
	import_item := checker.ast_module.imports[import_id]
	if import_item.target < 0 || 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: int) -> int {
	if find_import(checker, file, expr.qualifier) < 0 {
		return source.addf(checker.diagnostics, expr.span, "unknown package alias '%s'", expr.qualifier)
	}
	return source.addf(checker.diagnostics, expr.span, "unavailable imported package '%s'", expr.qualifier)
}

add_name_resolution_diagnostic :: proc(checker: ^Checker, expr: ast.Expr, target_pkg: int) -> int {
	if find_template(checker, expr.text, target_pkg) >= 0 {
		return source.addf(checker.diagnostics, expr.span, "'%s' is a function, not a global value", expr.text)
	}
	if expr.qualifier != "" {
		return source.addf(
			checker.diagnostics,
			expr.span,
			"package '%s' has no member '%s'",
			expr.qualifier,
			expr.text,
		)
	}
	return source.addf(checker.diagnostics, expr.span, "unresolved global '%s'", expr.text)
}

add_call_resolution_diagnostic :: proc(checker: ^Checker, expr: ast.Expr, target_pkg: int) -> int {
	if find_global(checker, expr.text, target_pkg) >= 0 {
		return source.addf(checker.diagnostics, expr.span, "'%s' is a global, not a function", expr.text)
	}
	if expr.qualifier != "" {
		return source.addf(
			checker.diagnostics,
			expr.span,
			"package '%s' has no member '%s'",
			expr.qualifier,
			expr.text,
		)
	}
	return source.addf(checker.diagnostics, expr.span, "unresolved function '%s'", expr.text)
}

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

mark_expr_imports_used :: proc(checker: ^Checker, expr_id, file: int) {
	if expr_id < 0 || expr_id >= len(checker.ast_module.exprs) {
		return
	}
	expr := checker.ast_module.exprs[expr_id]
	switch expr.kind {
	case .Name:
		if expr.qualifier != "" {
			_ = find_import(checker, file, expr.qualifier, true)
		}
	case .Call:
		if expr.qualifier != "" {
			_ = find_import(checker, file, expr.qualifier, true)
		}
		for arg in expr.args {
			mark_expr_imports_used(checker, arg, file)
		}
	case .Add:
		mark_expr_imports_used(checker, expr.left, file)
		mark_expr_imports_used(checker, expr.right, file)
	case .Invalid, .Integer:
	}
}

validate_declarations :: proc(checker: ^Checker) {
	for function in checker.ast_module.functions {
		locals: [dynamic]string
		locals.allocator = checker.allocator
		for param in function.params {
			if param.type == .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'",
					param.name,
				)
			}
			append(&locals, param.name)
		}
		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)
			case .Invalid:
			}
		}
		delete(locals)
	}
}

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

spec_signature_equal :: proc(spec: Spec, template: int, args: []types.Type) -> bool {
	if spec.template != template || len(spec.args) != len(args) {
		return false
	}
	for arg, index in args {
		if !types.equal(spec.args[index], arg) {
			return false
		}
	}
	return true
}

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

can_specialize :: proc(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 !types.is_concrete_integer(specialized_param_type(param.type, actual)) {
			return false
		}
	}
	return true
}

ensure_spec :: proc(checker: ^Checker, template: int, actual_args: []types.Type) -> int {
	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))
	}
	for spec, index in checker.specs {
		if spec_signature_equal(spec, template, signature[:]) {
			delete(signature)
			return index
		}
	}
	result := type_from_syntax(function.result)
	if function.pkg == 0 && function.name == "main" && function.result == .Int {
		result = types.I32
	}
	index := len(checker.specs)
	append(
		&checker.specs,
		Spec{template = template, args = signature[:], result = result, hir_id = -1},
	)
	return index
}

infer_expr :: proc(checker: ^Checker, expr_id: int, locals: []Infer_Local, pkg := 0, file := 0) -> types.Type {
	if expr_id < 0 || expr_id >= len(checker.ast_module.exprs) {
		return types.INVALID
	}
	constant := eval_constant(checker, expr_id)
	if constant.kind == .Overflow || (constant.kind == .Value && !fits_i64(constant.value)) {
		return types.I64
	}
	if constant.kind == .Value {
		return types.smallest_signed_for_literal(i64(constant.value))
	}
	expr := checker.ast_module.exprs[expr_id]
	switch expr.kind {
	case .Invalid:
		return types.INVALID
	case .Integer:
		return types.smallest_signed_for_literal(expr.integer)
	case .Name:
		if expr.qualifier == "" {
			local_type := find_infer_local(locals, expr.text)
			if types.is_valid(local_type) {
				return local_type
			}
		}
		target_pkg, available := expr_package(checker, expr, pkg, file)
		if !available {
			return types.INVALID
		}
		global := find_global(checker, expr.text, target_pkg)
		if global >= 0 {
			return checker.global_types[global]
		}
		return types.INVALID
	case .Add:
		left := infer_expr(checker, expr.left, locals, pkg, file)
		right := infer_expr(checker, expr.right, locals, pkg, file)
		return types.widest(left, right)
	case .Call:
		target_pkg, available := expr_package(checker, expr, pkg, file)
		if !available {
			return types.INVALID
		}
		template := find_template(checker, expr.text, target_pkg)
		if template < 0 {
			return types.INVALID
		}
		args := make([]types.Type, len(expr.args), checker.allocator)
		for arg, index in expr.args {
			args[index] = infer_expr(checker, arg, locals, pkg, file)
		}
		function := checker.ast_module.functions[template]
		if !can_specialize(function, args) {
			delete(args, checker.allocator)
			declared := type_from_syntax(function.result)
			if function.pkg == 0 && function.name == "main" && function.result == .Int {
				return types.I32
			}
			if declared.kind == .Concrete || declared.kind == .Void {
				return declared
			}
			return types.INVALID
		}
		spec := ensure_spec(checker, template, args)
		delete(args, checker.allocator)
		return checker.specs[spec].result
	}
	return types.INVALID
}

infer_spec_result :: proc(checker: ^Checker, spec_id: int) -> types.Type {
	spec := checker.specs[spec_id]
	function := checker.ast_module.functions[spec.template]
	declared := type_from_syntax(function.result)
	if function.pkg == 0 && function.name == "main" && function.result == .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)
			declared_local := type_from_syntax(statement.type)
			if declared_local.kind == .Concrete {
				value_type = declared_local
			}
			append(&locals, Infer_Local{name = statement.name, type = value_type})
		case .Assignment, .Expression:
			_ = infer_expr(checker, statement.expr, locals[:], function.pkg, function.file)
		case .Return:
			if statement.expr >= 0 {
				returned := infer_expr(checker, statement.expr, locals[:], function.pkg, function.file)
				if !types.is_valid(result) {
					result = returned
				} else {
					result = types.widest(result, returned)
				}
			}
		}
	}
	if declared.kind == .Int_Constraint {
		return result
	}
	return declared
}

merge_inferred_type :: proc(current: ^types.Type, inferred: types.Type) -> bool {
	if !types.is_concrete_integer(inferred) {
		return false
	}
	if !types.is_concrete_integer(current^) {
		current^ = inferred
		return true
	}
	merged := types.widest(current^, inferred)
	if types.is_concrete_integer(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 declared.kind == .Concrete {
			checker.global_types[index] = declared
		}
	}

	main_template := find_template(checker, "main", 0)
	if main_template >= 0 {
		ensure_spec(checker, main_template, nil)
	}

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

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

invalid_hir_expr :: proc(
	checker: ^Checker,
	span: source.Span,
	diagnostic: int,
	recovery_type := types.INVALID,
) -> int {
	return add_hir_expr(
		checker,
		hir.Expr {
			kind = .Invalid,
			span = span,
			type = recovery_type,
			target = -1,
			left = -1,
			right = -1,
			diagnostic = diagnostic,
		},
	)
}

add_unique :: proc(values: ^[dynamic]int, value: int) {
	for existing in values {
		if existing == value {
			return
		}
	}
	append(values, value)
}

find_build_local :: proc(locals: []Build_Local, name: string) -> (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: int,
	expected: types.Type,
	span: source.Span,
) -> int {
	if expr_id < 0 {
		return expr_id
	}
	actual := checker.module.exprs[expr_id].type
	if types.equal(actual, expected) {
		return expr_id
	}
	if types.can_widen(actual, expected) {
		return add_hir_expr(
			checker,
			hir.Expr {
				kind = .Widen,
				span = span,
				type = expected,
				left = expr_id,
				target = -1,
				right = -1,
				diagnostic = -1,
			},
		)
	}
	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,
) -> int {
	recovery_type := types.I64
	if types.is_signed(expected) {
		recovery_type = expected
	}
	if constant.kind == .Overflow || !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)
	result_type := types.smallest_signed_for_literal(value)
	if types.is_signed(expected) {
		if !fits_signed_type(constant.value, expected) {
			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 = -1,
			left = -1,
			right = -1,
			diagnostic = -1,
		},
	)
}

build_expr :: proc(
	checker: ^Checker,
	expr_id: int,
	locals: []Build_Local,
	global_reads: ^[dynamic]int,
	calls: ^[dynamic]int,
	expected := types.INVALID,
	pkg := 0,
	file := 0,
) -> int {
	if expr_id < 0 || expr_id >= len(checker.ast_module.exprs) {
		id := source.add(checker.diagnostics, source.Span{}, "missing expression")
		return invalid_hir_expr(checker, source.Span{}, id)
	}
	expr := checker.ast_module.exprs[expr_id]
	constant := eval_constant(checker, expr_id)
	if constant.kind == .Value || constant.kind == .Overflow {
		return build_constant_expr(checker, expr, constant, expected)
	}
	switch expr.kind {
	case .Invalid:
		return invalid_hir_expr(checker, expr.span, expr.diagnostic)
	case .Integer:
		unreachable()
	case .Name:
		if expr.qualifier == "" {
			if local, ok := find_build_local(locals, expr.text); ok {
				return add_hir_expr(
					checker,
					hir.Expr {
						kind = .Local,
						span = expr.span,
						type = local.type,
						target = local.id,
						left = -1,
						right = -1,
						diagnostic = -1,
					},
				)
			}
		}
		target_pkg, available := expr_package(checker, expr, pkg, file, true)
		if !available {
			id := add_package_resolution_diagnostic(checker, expr, file)
			return invalid_hir_expr(checker, expr.span, id)
		}
		global := find_global(checker, expr.text, target_pkg)
		if global >= 0 {
			add_unique(global_reads, global)
			return add_hir_expr(
				checker,
				hir.Expr {
					kind = .Global,
					span = expr.span,
					type = checker.global_types[global],
					target = global,
					left = -1,
					right = -1,
					diagnostic = -1,
				},
			)
		}
		id := add_name_resolution_diagnostic(checker, expr, target_pkg)
		return invalid_hir_expr(checker, expr.span, id)
	case .Add:
		left := build_expr(checker, expr.left, locals, global_reads, calls, types.INVALID, pkg, file)
		right := build_expr(checker, expr.right, locals, global_reads, calls, types.INVALID, pkg, file)
		left_type := checker.module.exprs[left].type
		right_type := checker.module.exprs[right].type
		result := types.widest(left_type, right_type)
		if !types.is_signed(result) {
			id := source.add(
				checker.diagnostics,
				expr.span,
				"addition requires compatible signed integers",
			)
			return invalid_hir_expr(checker, expr.span, id)
		}
		left = coerce_expr(checker, left, result, checker.module.exprs[left].span)
		right = coerce_expr(checker, right, result, checker.module.exprs[right].span)
		return add_hir_expr(
			checker,
			hir.Expr {
				kind = .Add,
				span = expr.span,
				type = result,
				left = left,
				right = right,
				target = -1,
				diagnostic = -1,
			},
		)
	case .Call:
		target_pkg, available := expr_package(checker, expr, pkg, file, true)
		if !available {
			id := add_package_resolution_diagnostic(checker, expr, file)
			return invalid_hir_expr(checker, expr.span, id)
		}
		template := find_template(checker, expr.text, target_pkg)
		if template < 0 {
			id := add_call_resolution_diagnostic(checker, expr, target_pkg)
			return invalid_hir_expr(checker, expr.span, id)
		}
		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",
				expr.text,
				len(checker.ast_module.functions[template].params),
				len(expr.args),
			)
			return invalid_hir_expr(checker, expr.span, id)
		}
		built_args := make([]int, len(expr.args), checker.allocator)
		arg_types := make([]types.Type, len(expr.args), checker.allocator)
		for arg, index in expr.args {
			arg_expected := type_from_syntax(checker.ast_module.functions[template].params[index].type)
			if arg_expected.kind != .Concrete {
				arg_expected = types.INVALID
			}
			built_args[index] = build_expr(
				checker,
				arg,
				locals,
				global_reads,
				calls,
				arg_expected,
				pkg,
				file,
			)
			arg_types[index] = checker.module.exprs[built_args[index]].type
		}
		spec := ensure_spec(checker, template, arg_types)
		delete(arg_types, checker.allocator)
		for _, index in built_args {
			built_args[index] = coerce_expr(
				checker,
				built_args[index],
				checker.specs[spec].args[index],
				checker.module.exprs[built_args[index]].span,
			)
		}
		add_unique(calls, spec)
		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'",
				expr.text,
			)
			delete(built_args, checker.allocator)
			return invalid_hir_expr(checker, expr.span, id)
		}
		return add_hir_expr(
			checker,
			hir.Expr {
				kind = .Call,
				span = expr.span,
				type = result,
				target = spec,
				left = -1,
				right = -1,
				args = built_args,
				diagnostic = -1,
			},
		)
	}
	return invalid_hir_expr(
		checker,
		expr.span,
		source.add(checker.diagnostics, expr.span, "invalid expression"),
	)
}

make_link_name :: proc(checker: ^Checker, spec_id: int) -> string {
	spec := checker.specs[spec_id]
	function := checker.ast_module.functions[spec.template]
	if function.pkg == 0 && function.name == "main" {
		return fmt.aprintf("main", 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, function.name)
	for arg in spec.args {
		strings.write_string(&builder, "__")
		strings.write_string(&builder, types.name(arg))
	}
	return fmt.aprintf("%s", strings.to_string(builder), allocator = checker.allocator)
}

build_function :: proc(checker: ^Checker, spec_id: int) {
	if checker.specs[spec_id].hir_id >= 0 {
		return
	}
	spec := checker.specs[spec_id]
	function := checker.ast_module.functions[spec.template]
	signature_diagnostic := -1
	if spec.result.kind != .Void && !types.is_concrete_integer(spec.result) {
		checker.specs[spec_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'",
			function.name,
		)
	}
	for arg in spec.args {
		if !types.is_concrete_integer(arg) {
			signature_diagnostic = source.addf(
				checker.diagnostics,
				function.span,
				"could not resolve a concrete parameter type for '%s'",
				function.name,
			)
			break
		}
	}
	hir_id := len(checker.module.functions)
	checker.specs[spec_id].hir_id = hir_id

	locals: [dynamic]Build_Local
	locals.allocator = checker.allocator
	hir_locals: [dynamic]hir.Local
	hir_locals.allocator = checker.allocator
	params: [dynamic]int
	params.allocator = checker.allocator
	body: [dynamic]int
	body.allocator = checker.allocator
	global_reads: [dynamic]int
	global_reads.allocator = checker.allocator
	calls: [dynamic]int
	calls.allocator = checker.allocator

	for param, index in function.params {
		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 >= 0
	has_return := false
	if signature_diagnostic >= 0 {
		append(&body, len(checker.module.statements))
		append(
			&checker.module.statements,
			hir.Stmt {
				kind = .Trap,
				span = function.span,
				expr = -1,
				local = -1,
				diagnostic = signature_diagnostic,
			},
		)
	}
	for statement_id in function.body {
		statement := checker.ast_module.statements[statement_id]
		switch statement.kind {
		case .Declaration:
			declared := type_from_syntax(statement.type)
			expected := types.INVALID
			if declared.kind == .Concrete {
				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 declared.kind == .Concrete {
				value = coerce_expr(checker, value, declared, statement.span)
				value_type = checker.module.exprs[value].type
			} else if declared.kind == .Void {
				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'",
					statement.name,
				)
				append(&body, len(checker.module.statements))
				append(
					&checker.module.statements,
					hir.Stmt {
						kind = .Trap,
						span = statement.span,
						expr = -1,
						local = -1,
						diagnostic = id,
					},
				)
				problematic = true
				continue
			}
			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, len(checker.module.statements))
			append(
				&checker.module.statements,
				hir.Stmt {
					kind = .Declaration,
					span = statement.span,
					local = local_id,
					expr = value,
					diagnostic = -1,
				},
			)
			problematic = problematic || checker.module.exprs[value].kind == .Invalid
		case .Assignment:
			if statement.name == "_" {
				value := build_expr(checker, statement.expr, locals[:], &global_reads, &calls, types.INVALID, function.pkg, function.file)
				if checker.module.exprs[value].type.kind == .Void {
					id := source.add(
						checker.diagnostics,
						statement.span,
						"cannot assign a void expression to '_'",
					)
					append(&body, len(checker.module.statements))
					append(
						&checker.module.statements,
						hir.Stmt {
							kind = .Trap,
							span = statement.span,
							expr = -1,
							local = -1,
							diagnostic = id,
						},
					)
					problematic = true
				} else {
					append(&body, len(checker.module.statements))
					append(
						&checker.module.statements,
						hir.Stmt {
							kind = .Sink,
							span = statement.span,
							expr = value,
							local = -1,
							diagnostic = -1,
						},
					)
				}
				continue
			}
			local, found := find_build_local(locals[:], statement.name)
			if !found {
				id := source.addf(
					checker.diagnostics,
					statement.span,
					"cannot assign unresolved local '%s'",
					statement.name,
				)
				append(&body, len(checker.module.statements))
				append(
					&checker.module.statements,
					hir.Stmt {
						kind = .Trap,
						span = statement.span,
						expr = -1,
						local = -1,
						diagnostic = id,
					},
				)
				problematic = true
				continue
			}
			if !local.mutable {
				id := source.addf(
					checker.diagnostics,
					statement.span,
					"cannot assign immutable local '%s'",
					statement.name,
				)
				append(&body, len(checker.module.statements))
				append(
					&checker.module.statements,
					hir.Stmt {
						kind = .Trap,
						span = statement.span,
						expr = -1,
						local = -1,
						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, len(checker.module.statements))
			append(
				&checker.module.statements,
				hir.Stmt {
					kind = .Assignment,
					span = statement.span,
					expr = value,
					local = local.id,
					diagnostic = -1,
				},
			)
			problematic = problematic || checker.module.exprs[value].kind == .Invalid
		case .Return:
			has_return = true
			if statement.expr < 0 {
				if spec.result.kind != .Void {
					id := source.add(
						checker.diagnostics,
						statement.span,
						"'return _' is only valid in a void function",
					)
					append(&body, len(checker.module.statements))
					append(
						&checker.module.statements,
						hir.Stmt {
							kind = .Trap,
							span = statement.span,
							expr = -1,
							local = -1,
							diagnostic = id,
						},
					)
					problematic = true
				} else {
					append(&body, len(checker.module.statements))
					append(
						&checker.module.statements,
						hir.Stmt {
							kind = .Return,
							span = statement.span,
							expr = -1,
							local = -1,
							diagnostic = -1,
						},
					)
				}
				continue
			}
			if spec.result.kind == .Void {
				id := source.add(
					checker.diagnostics,
					statement.span,
					"void function cannot return a value",
				)
				append(&body, len(checker.module.statements))
				append(
					&checker.module.statements,
					hir.Stmt {
						kind = .Trap,
						span = statement.span,
						expr = -1,
						local = -1,
						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, len(checker.module.statements))
			append(
				&checker.module.statements,
				hir.Stmt {
					kind = .Return,
					span = statement.span,
					expr = value,
					local = -1,
					diagnostic = -1,
				},
			)
			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 checker.module.exprs[value].type.kind != .Void {
				id := source.add(
					checker.diagnostics,
					statement.span,
					"non-void expression result must be consumed or assigned to '_'",
				)
				append(&body, len(checker.module.statements))
				append(
					&checker.module.statements,
					hir.Stmt {
						kind = .Trap,
						span = statement.span,
						expr = -1,
						local = -1,
						diagnostic = id,
					},
				)
				problematic = true
			} else {
				append(&body, len(checker.module.statements))
				append(
					&checker.module.statements,
					hir.Stmt {
						kind = .Expression,
						span = statement.span,
						expr = value,
						local = -1,
						diagnostic = -1,
					},
				)
			}
		case .Invalid:
			append(&body, len(checker.module.statements))
			append(
				&checker.module.statements,
				hir.Stmt {
					kind = .Trap,
					span = statement.span,
					expr = -1,
					local = -1,
					diagnostic = statement.diagnostic,
				},
			)
			problematic = true
		}
	}

	if spec.result.kind != .Void && !has_return {
		id := source.addf(
			checker.diagnostics,
			function.span,
			"function '%s' does not return a value",
			function.name,
		)
		append(&body, len(checker.module.statements))
		append(
			&checker.module.statements,
			hir.Stmt{kind = .Trap, span = function.span, expr = -1, local = -1, diagnostic = id},
		)
		problematic = true
	}

	append(
		&checker.module.functions,
		hir.Function {
			name = function.name,
			link_name = make_link_name(checker, spec_id),
			c_abi = function.c_abi || (function.pkg == 0 && function.name == "main"),
			is_main = function.pkg == 0 && function.name == "main",
			params = params[:],
			result = spec.result,
			locals = hir_locals[:],
			body = body[:],
			direct_global_reads = global_reads[:],
			calls = calls[:],
			problematic = problematic,
			diagnostic = -1,
		},
	)
	delete(locals)
}

expr_problematic :: proc(module: ^hir.Module, expr_id: int) -> bool {
	if expr_id < 0 || expr_id >= len(module.exprs) {
		return true
	}
	expr := module.exprs[expr_id]
	if expr.kind == .Invalid {
		return true
	}
	if expr.left >= 0 && expr_problematic(module, expr.left) {
		return true
	}
	if expr.right >= 0 && expr_problematic(module, expr.right) {
		return true
	}
	for arg in expr.args {
		if expr_problematic(module, arg) {
			return true
		}
	}
	return false
}

build_globals :: proc(checker: ^Checker) {
	for global, global_id in checker.ast_module.globals {
		dependencies: [dynamic]int
		dependencies.allocator = checker.allocator
		calls: [dynamic]int
		calls.allocator = checker.allocator
		declared := type_from_syntax(global.type)
		expected := types.INVALID
		if declared.kind == .Concrete {
			expected = declared
		}
		expr := build_expr(checker, global.expr, nil, &dependencies, &calls, expected, global.pkg, global.file)
		global_type := checker.global_types[global_id]
		if declared.kind == .Concrete {
			expr = coerce_expr(checker, expr, declared, global.span)
			global_type = checker.module.exprs[expr].type
		} else if types.is_concrete_integer(checker.module.exprs[expr].type) {
			global_type = checker.module.exprs[expr].type
		}
		diagnostic := -1
		if !types.is_concrete_integer(global_type) {
			diagnostic = source.addf(
				checker.diagnostics,
				global.span,
				"could not resolve a concrete type for global '%s'",
				global.name,
			)
			global_type = types.I64
			expr = invalid_hir_expr(checker, global.span, diagnostic, global_type)
		}
		if global.type == .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 < 0
		static_value: i64
		if is_static {
			static_value = checker.module.exprs[expr].integer
		}
		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.module, expr),
				problematic = expr_problematic(&checker.module, 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 >= 0 && call < len(checker.specs) {
					hir_id := checker.specs[call].hir_id
					if hir_id >= 0 && checker.module.functions[hir_id].problematic {
						function.problematic = true
						changed = true
						break
					}
				}
			}
		}
		for &global in checker.module.globals {
			if global.problematic {
				continue
			}
			for dependency in global.dependencies {
				if dependency >= 0 &&
				   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 >= 0 && call < len(checker.specs) {
					hir_id := checker.specs[call].hir_id
					if hir_id >= 0 && checker.module.functions[hir_id].problematic {
						global.problematic = true
						changed = true
						break
					}
				}
			}
		}
	}
}

resolve_call_targets :: proc(checker: ^Checker) {
	for &expr in checker.module.exprs {
		if expr.kind == .Call && expr.target >= 0 && expr.target < len(checker.specs) {
			expr.target = checker.specs[expr.target].hir_id
		}
	}
}

append_unique_slice :: proc(values: ^[]int, value: int, allocator: mem.Allocator) -> bool {
	for existing in values^ {
		if existing == value {
			return false
		}
	}
	replacement := make([]int, len(values^) + 1, allocator)
	copy(replacement, values^)
	replacement[len(values^)] = value
	delete(values^, allocator)
	values^ = replacement
	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 < 0 || call >= len(checker.specs) {
					continue
				}
				callee := checker.specs[call].hir_id
				if callee < 0 || callee >= len(checker.module.functions) {
					continue
				}
				for global_id in checker.module.functions[callee].direct_global_reads {
					if append_unique_slice(
						&function.direct_global_reads,
						global_id,
						checker.allocator,
					) {
						changed = true
					}
				}
			}
		}
	}
	for &global in checker.module.globals {
		for call in global.calls {
			if call < 0 || call >= len(checker.specs) {
				continue
			}
			function_id := checker.specs[call].hir_id
			if function_id < 0 || function_id >= len(checker.module.functions) {
				continue
			}
			for dependency in checker.module.functions[function_id].direct_global_reads {
				_ = append_unique_slice(&global.dependencies, dependency, checker.allocator)
			}
		}
	}
}

detect_global_cycles_visit :: proc(checker: ^Checker, global_id: int, states: []u8) {
	if states[global_id] == 2 {
		return
	}
	if states[global_id] == 1 {
		id := source.addf(
			checker.diagnostics,
			checker.ast_module.globals[global_id].span,
			"global initialization cycle involving '%s'",
			checker.module.globals[global_id].name,
		)
		checker.module.globals[global_id].diagnostic = id
		checker.module.globals[global_id].problematic = true
		return
	}
	states[global_id] = 1
	for dependency in checker.module.globals[global_id].dependencies {
		if dependency >= 0 && dependency < len(states) {
			detect_global_cycles_visit(checker, dependency, states)
			if checker.module.globals[dependency].problematic {
				checker.module.globals[global_id].problematic = true
			}
		}
	}
	states[global_id] = 2
}

synthesize_trap_main :: proc(checker: ^Checker) {
	id := source.add(checker.diagnostics, source.Span{}, "missing or unusable main function")
	statement_id := len(checker.module.statements)
	append(
		&checker.module.statements,
		hir.Stmt{kind = .Trap, span = source.Span{}, expr = -1, local = -1, diagnostic = id},
	)
	body := make([]int, 1, checker.allocator)
	body[0] = statement_id
	append(
		&checker.module.functions,
		hir.Function {
			name = "main",
			link_name = fmt.aprintf("main", allocator = checker.allocator),
			c_abi = true,
			is_main = true,
			result = types.VOID,
			body = body,
			problematic = true,
			diagnostic = id,
		},
	)
}

replace_main_with_trap :: proc(checker: ^Checker, diagnostic: int) {
	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.problematic = true
		function.diagnostic = diagnostic
		statement_id := len(checker.module.statements)
		append(
			&checker.module.statements,
			hir.Stmt {
				kind = .Trap,
				span = source.Span{},
				expr = -1,
				local = -1,
				diagnostic = diagnostic,
			},
		)
		function.body = make([]int, 1, checker.allocator)
		function.body[0] = statement_id
		return
	}
	synthesize_trap_main(checker)
}

check :: proc(
	ast_module: ^ast.Module,
	diagnostics: ^source.Diagnostics,
	allocator := context.allocator,
) -> hir.Module {
	checker := Checker {
		ast_module  = ast_module,
		diagnostics = diagnostics,
		module      = hir.init_module(allocator),
		allocator   = allocator,
	}
	checker.specs.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)
	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)
	}

	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'", 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", 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'", global.name)
			}
		}
	}

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

	main_template := find_template(&checker, "main", 0)
	main_declarations := 0
	for function in ast_module.functions {
		if function.pkg == 0 && function.name == "main" {
			main_declarations += 1
		}
	}
	if main_declarations == 0 {
		synthesize_trap_main(&checker)
	} else {
		template := ast_module.functions[main_template]
		if main_declarations != 1 ||
		   len(template.params) != 0 ||
		   !(template.result == .Void || template.result == .I32 || template.result == .Int) {
			id := source.add(
				diagnostics,
				template.span,
				"main must be unique, 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 global_id in 0 ..< len(checker.module.globals) {
		detect_global_cycles_visit(&checker, global_id, 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'", import_item.alias)
		}
	}
	return checker.module
}