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// Copyright (c) 2015, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.
import 'dart:collection';
import 'package:kernel/kernel.dart';
import '../compiler/js_names.dart' as js_ast;
import '../compiler/module_containers.dart'
show ModuleItemContainer, ModuleItemData;
import '../js_ast/js_ast.dart' as js_ast;
import '../js_ast/js_ast.dart' show js;
import 'kernel_helpers.dart';
/// Returns all non-locally defined type parameters referred to by [t].
Set<TypeParameter> freeTypeParameters(DartType t) {
var result = <TypeParameter>{};
void find(DartType t) {
if (t is TypeParameterType) {
} else if (t is InterfaceType) {
} else if (t is FutureOrType) {
} else if (t is TypedefType) {
} else if (t is FunctionType) {
t.namedParameters.forEach((n) => find(n.type));
t.typeParameters.forEach((p) => find(p.bound));
return result;
/// A name for a type made of JS identifier safe characters.
/// 'L' and 'N' are appended to a type name to represent a legacy or nullable
/// flavor of a type.
String _typeString(DartType type, {bool flat = false}) {
var nullability = type.declaredNullability == Nullability.legacy
? 'L'
: type.declaredNullability == Nullability.nullable
? 'N'
: '';
if (type is InterfaceType) {
var name = '${}$nullability';
var typeArgs = type.typeArguments;
if (typeArgs.isEmpty) return name;
if (typeArgs.every((p) => p == const DynamicType())) return name;
return "${name}Of${"\$")}";
if (type is FutureOrType) {
var name = 'FutureOr$nullability';
if (type.typeArgument == const DynamicType()) return name;
return '${name}Of${_typeString(type.typeArgument)}';
if (type is TypedefType) {
var name = '${}$nullability';
var typeArgs = type.typeArguments;
if (typeArgs.isEmpty) return name;
if (typeArgs.every((p) => p == const DynamicType())) return name;
return "${name}Of${"\$")}";
if (type is FunctionType) {
if (flat) return 'Fn';
var rType = _typeString(type.returnType, flat: true);
var params = type.positionalParameters
.map((p) => _typeString(p, flat: true));
var paramList = params.join('And');
var count = type.positionalParameters.length;
if (count > 3 || type.namedParameters.isNotEmpty) {
paramList = '${paramList}__';
} else if (count == 0) {
paramList = 'Void';
return '${paramList}To$nullability$rType';
if (type is TypeParameterType) return '${}$nullability';
if (type is DynamicType) return 'dynamic';
if (type is VoidType) return 'void';
if (type is NeverType) return 'Never$nullability';
if (type is NullType) return 'Null';
return 'invalid';
class TypeTable {
/// Mapping from type parameters to the types which must have their
/// cache/generator variables discharged at the binding site for the
/// type variable since the type definition depends on the type
/// parameter.
final _scopeDependencies = <TypeParameter, List<DartType>>{};
/// Contains types with any free type parameters and maps them to a unique
/// JS identifier.
/// Used to reference types hoisted to the top of a generic class or generic
/// function (as opposed to the top of the entire module).
final _unboundTypeIds = HashMap<DartType, js_ast.Identifier>();
/// Holds JS type generators keyed by their underlying DartType.
final typeContainer = ModuleItemContainer<DartType>.asObject('T',
keyToString: (DartType t) => escapeIdentifier(_typeString(t))!);
final js_ast.Expression Function(String, [List<Object>]) _runtimeCall;
/// Returns true if [type] is already recorded in the table.
bool _isNamed(DartType type) =>
typeContainer.contains(type) || _unboundTypeIds.containsKey(type);
Set<Library> incrementalLibraries() {
var libraries = <Library>{};
for (var t in typeContainer.incrementalModuleItems) {
if (t is InterfaceType) {
return libraries;
/// Emit the initializer statements for the type container, which contains
/// all named types with fully bound type parameters.
List<js_ast.Statement> dischargeBoundTypes() {
js_ast.Expression emitValue(DartType t, ModuleItemData data) {
var access ='#.#', [, data.jsKey]);
return'() => ((# = #)())', [
_runtimeCall('constFn(#)', [data.jsValue])
var boundTypes = typeContainer.emit(emitValue: emitValue);
// Bound types should only be emitted once (even across multiple evals).
for (var t in typeContainer.keys) {
return boundTypes;
js_ast.Statement _dischargeFreeType(DartType type) {
var init = typeContainer[type]!;
var id = _unboundTypeIds[type]!;
// TODO(vsm): Change back to `let`.
// See
return js.statement('var # = () => ((# = #)());', [
_runtimeCall('constFn(#)', [init])
/// Emit a list of statements declaring the cache variables and generator
/// definitions tracked by the table so far.
/// If [formals] is present, only emit the definitions which depend on the
/// formals.
List<js_ast.Statement> dischargeFreeTypes(
[Iterable<TypeParameter>? formals]) {
var decls = <js_ast.Statement>[];
var types = formals == null
? typeContainer.keys.where((p) => freeTypeParameters(p).isNotEmpty)
: formals.expand((p) => _scopeDependencies[p] ?? <DartType>[]).toSet();
for (var t in types) {
var stmt = _dischargeFreeType(t);
return decls;
/// Emit a JS expression that evaluates to the generator for [type].
/// If [type] does not already have a generator name chosen for it,
/// assign it one, using [typeRep] as its initializer.
js_ast.Expression _nameType(DartType type, js_ast.Expression typeRep) {
if (!typeContainer.contains(type)) {
typeContainer[type] = typeRep;
return _unboundTypeIds[type] ?? typeContainer.access(type);
/// Record the dependencies of the type on its free variables.
/// Returns true if [type] is a free type parameter (but not a bound) and so
/// is not locally hoisted.
bool recordScopeDependencies(DartType type) {
if (_isNamed(type)) {
return false;
var freeVariables = freeTypeParameters(type);
// TODO(leafp): This is a hack to avoid trying to hoist out of
// generic functions and generic function types. This often degrades
// readability to little or no benefit. It would be good to do this
// when we know that we can hoist it to an outer scope, but for
// now we just disable it.
if (freeVariables.any((i) => i.parent is FunctionNode)) {
return true;
// This is only reached when [type] is itself a bound that depends on a
// free type parameter.
// TODO(markzipan): Bounds are locally hoisted to their own JS identifiers,
// but we don't do this this for other types that depend on free variables,
// resulting in some duplicated runtime code. We may get some performance
// wins if we just locally hoist everything.
if (freeVariables.isNotEmpty) {
// TODO(40273) Remove prepended text when we have a better way to hide
// these names from debug tools.
_unboundTypeIds[type] =
for (var free in freeVariables) {
// If `free` is a promoted type parameter, get the original one so we can
// find it in our map.
_scopeDependencies.putIfAbsent(free, () => []).add(type);
return false;
/// Given a type [type], and a JS expression [typeRep] which implements it,
/// add the type and its representation to the table, returning an
/// expression which implements the type (but which caches the value).
js_ast.Expression nameType(DartType type, js_ast.Expression typeRep) {
if (recordScopeDependencies(type)) {
return typeRep;
var name = _nameType(type, typeRep);
return'#()', [name]);
/// Like [nameType] but for function types.
/// The boolean parameter [lazy] indicates that the resulting expression
/// should be a function that is invoked to compute the type, rather than the
/// type itself. This allows better integration with `lazyFn`, avoiding an
/// extra level of indirection.
js_ast.Expression nameFunctionType(
FunctionType type, js_ast.Expression typeRep,
{bool lazy = false}) {
if (recordScopeDependencies(type)) {
return lazy ? js_ast.ArrowFun([], typeRep) : typeRep;
var name = _nameType(type, typeRep);
return lazy ? name :'#()', [name]);