[interop] Add Support for Function Declarations

web_generator/lib/src/ast/base.dart

@@ -0,0 +1,75 @@
+// Copyright (c) 2025, 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 'package:code_builder/code_builder.dart';
+
+import '../interop_gen/namer.dart';
+import 'types.dart';
+
+class GlobalOptions {
+  static int variardicArgsCount = 4;
+  static bool shouldEmitJsTypes = false;
+}
+
+class Options {}
+
+class DeclarationOptions extends Options {
+  DeclarationOptions();
+
+  TypeOptions toTypeOptions({bool nullable = false}) =>
+      TypeOptions(nullable: nullable);
+}
+
+class TypeOptions extends Options {
+  bool nullable;
+
+  TypeOptions({this.nullable = false});
+}
+
+class ASTOptions {
+  bool parameter;
+  bool emitJSTypes;
+  int variardicArgsCount;
+
+  ASTOptions(
+      {this.parameter = false,
+      this.variardicArgsCount = 4,
+      this.emitJSTypes = false});
+}
+
+sealed class Node {
+  abstract final String? name;
+  abstract final ID id;
+  String? get dartName;
+
+  Spec emit([Options? options]);
+
+  Node();
+}
+
+abstract class Declaration extends Node {
+  @override
+  abstract final String name;
+
+  @override
+  Spec emit([covariant DeclarationOptions? options]);
+}
+
+abstract class NamedDeclaration extends Declaration {
+  ReferredType asReferredType([List<Type>? typeArgs]) =>
+      ReferredType(name: name, declaration: this, typeParams: typeArgs ?? []);
+}
+
+abstract interface class ExportableDeclaration extends Declaration {
+  /// Whether this declaration is exported.
+  bool get exported;
+}
+
+abstract class Type extends Node {
+  @override
+  String? dartName;
+
+  @override
+  Reference emit([covariant TypeOptions? options]);
+}

web_generator/lib/src/ast/builtin.dart

@@ -0,0 +1,123 @@
+// Copyright (c) 2025, 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.
+
+// ignore_for_file: non_constant_identifier_names
+
+import 'package:code_builder/code_builder.dart';
+
+import '../interop_gen/namer.dart';
+import 'base.dart';
+
+/// A built in type supported by `dart:js_interop` or by this library
+/// (with generated declarations)
+class BuiltinType extends Type {
+  @override
+  final String name;
+
+  final List<Type> typeParams;
+
+  /// Whether the given type is present in "dart:js_interop"
+  final bool fromDartJSInterop;
+
+  // TODO(nikeokoronkwo): Types in general should have an `isNullable`
+  //  property on them to indicate nullability for Dart generated code.
+  final bool? isNullable;
+
+  BuiltinType(
+      {required this.name,
+      this.typeParams = const [],
+      this.fromDartJSInterop = false,
+      this.isNullable});
+
+  @override
+  ID get id => ID(type: 'type', name: name);
+
+  @override
+  String? get dartName => null;
+
+  @override
+  Reference emit([TypeOptions? options]) {
+    options ??= TypeOptions();
+
+    return TypeReference((t) => t
+      ..symbol = name
+      ..types.addAll(typeParams
+          // if there is only one type param, and it is void, ignore
+          .where((p) => typeParams.length != 1 || p != $voidType)
+          .map((p) => p.emit(TypeOptions())))
+      ..url = fromDartJSInterop ? 'dart:js_interop' : null
+      ..isNullable = isNullable ?? options!.nullable);
+  }
+
+  static final BuiltinType $voidType = BuiltinType(name: 'void');
+  static final BuiltinType anyType =
+      BuiltinType(name: 'JSAny', fromDartJSInterop: true, isNullable: true);
+
+  static BuiltinType primitiveType(PrimitiveType typeIdentifier,
+      {bool? shouldEmitJsType,
+      bool? isNullable,
+      List<Type> typeParams = const []}) {
+    shouldEmitJsType ??= GlobalOptions.shouldEmitJsTypes;
+    return switch (typeIdentifier) {
+      PrimitiveType.int => shouldEmitJsType
+          ? BuiltinType(
+              name: 'JSNumber', fromDartJSInterop: true, isNullable: isNullable)
+          : BuiltinType(name: 'int', isNullable: isNullable),
+      PrimitiveType.num => shouldEmitJsType
+          ? BuiltinType(
+              name: 'JSNumber', fromDartJSInterop: true, isNullable: isNullable)
+          : BuiltinType(name: 'num', isNullable: isNullable),
+      PrimitiveType.double => shouldEmitJsType
+          ? BuiltinType(
+              name: 'JSNumber', fromDartJSInterop: true, isNullable: isNullable)
+          : BuiltinType(name: 'double', isNullable: isNullable),
+      PrimitiveType.boolean => shouldEmitJsType
+          ? BuiltinType(
+              name: 'JSBoolean',
+              fromDartJSInterop: true,
+              isNullable: isNullable)
+          : BuiltinType(name: 'bool', isNullable: isNullable),
+      PrimitiveType.string => shouldEmitJsType
+          ? BuiltinType(
+              name: 'JSString', fromDartJSInterop: true, isNullable: isNullable)
+          : BuiltinType(name: 'String', isNullable: isNullable),
+      PrimitiveType.$void => $voidType,
+      PrimitiveType.any => anyType,
+      PrimitiveType.object => BuiltinType(
+          name: 'JSObject', fromDartJSInterop: true, isNullable: isNullable),
+      PrimitiveType.unknown =>
+        BuiltinType(name: 'JSAny', fromDartJSInterop: true, isNullable: true),
+      PrimitiveType.undefined =>
+        BuiltinType(name: 'JSAny', fromDartJSInterop: true, isNullable: true),
+      PrimitiveType.array => BuiltinType(
+          name: 'JSArray',
+          typeParams: [typeParams.single],
+          fromDartJSInterop: true,
+          isNullable: isNullable),
+      PrimitiveType.promise => BuiltinType(
+          name: 'JSPromise',
+          typeParams: [typeParams.single],
+          fromDartJSInterop: true,
+          isNullable: isNullable),
+      PrimitiveType.function => BuiltinType(
+          name: 'JSFunction', fromDartJSInterop: true, isNullable: isNullable),
+    };
+  }
+}
+
+enum PrimitiveType {
+  int,
+  num,
+  double,
+  boolean,
+  string,
+  $void,
+  any,
+  object,
+  unknown,
+  undefined,
+  array,
+  promise,
+  function
+}