Add support for extension types (dart-archive/code_builder#437)

Corresponds to the syntax defined in https://github.com/dart-lang/language/blob/main/accepted/future-releases/extension-types/feature-specification.md#syntax.

pkgs/code_builder/.github/workflows/test-package.yml

@@ -43,7 +43,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ubuntu-latest]
-        sdk: [2.19.0, dev]
+        sdk: [3.0.0, dev]
     steps:
       - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11
       - uses: dart-lang/setup-dart@b64355ae6ca0b5d484f0106a033dd1388965d06d

pkgs/code_builder/CHANGELOG.md

@@ -1,4 +1,4 @@
-## 4.8.0-wip
+## 4.8.0
 
 * Add `Expression.operatorSubtract`
 * Deprecate `Expression.operatorSubstract`
@@ -28,6 +28,8 @@
 * Add `Expression.bitwiseXorAssign`
 * Add `Expression.bitwiseOrAssign`
 * Allow passing an `Expression` through `literal` without an exception.
+* Add support for extension types.
+* Update SDK version constraints to `>=3.0.0`.
 
 ## 4.7.0
 

pkgs/code_builder/lib/code_builder.dart

@@ -48,6 +48,7 @@ export 'src/specs/expression.dart'
         literalString,
         literalTrue;
 export 'src/specs/extension.dart' show Extension, ExtensionBuilder;
+export 'src/specs/extension_type.dart' show ExtensionType, ExtensionTypeBuilder;
 export 'src/specs/field.dart' show Field, FieldBuilder, FieldModifier;
 export 'src/specs/library.dart' show Library, LibraryBuilder;
 export 'src/specs/method.dart'

pkgs/code_builder/lib/src/emitter.dart

@@ -11,6 +11,7 @@ import 'specs/directive.dart';
 import 'specs/enum.dart';
 import 'specs/expression.dart';
 import 'specs/extension.dart';
+import 'specs/extension_type.dart';
 import 'specs/field.dart';
 import 'specs/library.dart';
 import 'specs/method.dart';
@@ -336,6 +337,62 @@ class DartEmitter extends Object
     return out;
   }
 
+  @override
+  StringSink visitExtensionType(ExtensionType spec, [StringSink? output]) {
+    final out = output ??= StringBuffer();
+    spec.docs.forEach(out.writeln);
+    for (var a in spec.annotations) {
+      visitAnnotation(a, out);
+    }
+
+    out.write('extension type ');
+    if (spec.constant) out.write('const ');
+    out.write(spec.name);
+    visitTypeParameters(spec.types.map((r) => r.type), out);
+    if (spec.primaryConstructorName.isNotEmpty) {
+      out.write('.${spec.primaryConstructorName}');
+    }
+    out.write('(');
+    _visitRepresentationDeclaration(spec.representationDeclaration, out);
+    out.write(')');
+
+    if (spec.implements.isNotEmpty) {
+      out
+        ..write(' implements ')
+        ..writeAll(
+            spec.implements.map<StringSink>((m) => m.type.accept(this)), ',');
+    }
+
+    out.writeln(' {');
+    for (var c in spec.constructors) {
+      visitConstructor(c, spec.name, out);
+      out.writeln();
+    }
+    for (var f in spec.fields) {
+      visitField(f, out);
+      out.writeln();
+    }
+    for (var m in spec.methods) {
+      visitMethod(m, out);
+      if (_isLambdaMethod(m)) {
+        out.writeln(';');
+      }
+      out.writeln();
+    }
+    out.writeln('}');
+    return out;
+  }
+
+  void _visitRepresentationDeclaration(
+      RepresentationDeclaration spec, StringSink out) {
+    spec.docs.forEach(out.writeln);
+    for (var a in spec.annotations) {
+      visitAnnotation(a, out);
+    }
+    spec.declaredRepresentationType.accept(this, out);
+    out.write(' ${spec.name}');
+  }
+
   @override
   StringSink visitDirective(Directive spec, [StringSink? output]) {
     output ??= StringBuffer();

pkgs/code_builder/lib/src/mixins/annotations.dart

@@ -7,13 +7,13 @@ import 'package:built_collection/built_collection.dart';
 import '../specs/expression.dart';
 
 /// A type of AST node that can have metadata [annotations].
-abstract class HasAnnotations {
+abstract mixin class HasAnnotations {
   /// Annotations as metadata on the node.
   BuiltList<Expression> get annotations;
 }
 
 /// Compliment to the [HasAnnotations] mixin for metadata [annotations].
-abstract class HasAnnotationsBuilder {
+abstract mixin class HasAnnotationsBuilder {
   /// Annotations as metadata on the node.
   abstract ListBuilder<Expression> annotations;
 }

pkgs/code_builder/lib/src/mixins/dartdoc.dart

@@ -4,12 +4,12 @@
 
 import 'package:built_collection/built_collection.dart';
 
-abstract class HasDartDocs {
+abstract mixin class HasDartDocs {
   /// Dart docs.
   BuiltList<String> get docs;
 }
 
-abstract class HasDartDocsBuilder {
+abstract mixin class HasDartDocsBuilder {
   /// Dart docs.
   abstract ListBuilder<String> docs;
 }

pkgs/code_builder/lib/src/mixins/generics.dart

@@ -6,12 +6,12 @@ import 'package:built_collection/built_collection.dart';
 
 import '../specs/reference.dart';
 
-abstract class HasGenerics {
+abstract mixin class HasGenerics {
   /// Generic type parameters.
   BuiltList<Reference> get types;
 }
 
-abstract class HasGenericsBuilder {
+abstract mixin class HasGenericsBuilder {
   /// Generic type parameters.
   abstract ListBuilder<Reference> types;
 }

pkgs/code_builder/lib/src/specs/code.dart

@@ -87,7 +87,7 @@ abstract class CodeVisitor<T> implements SpecVisitor<T> {
 }
 
 /// Knowledge of how to write valid Dart code from [CodeVisitor].
-abstract class CodeEmitter implements CodeVisitor<StringSink> {
+abstract mixin class CodeEmitter implements CodeVisitor<StringSink> {
   @protected
   Allocator get allocator;
 

pkgs/code_builder/lib/src/specs/expression.dart

@@ -526,7 +526,8 @@ abstract class ExpressionVisitor<T> implements SpecVisitor<T> {
 /// Knowledge of how to write valid Dart code from [ExpressionVisitor].
 ///
 /// **INTERNAL ONLY**.
-abstract class ExpressionEmitter implements ExpressionVisitor<StringSink> {
+abstract mixin class ExpressionEmitter
+    implements ExpressionVisitor<StringSink> {
   @override
   StringSink visitToCodeExpression(ToCodeExpression expression,
       [StringSink? output]) {

pkgs/code_builder/lib/src/specs/extension_type.dart

@@ -0,0 +1,152 @@
+// Copyright (c) 2023, 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:built_collection/built_collection.dart';
+import 'package:built_value/built_value.dart';
+import 'package:meta/meta.dart';
+
+import '../base.dart';
+import '../mixins/annotations.dart';
+import '../mixins/dartdoc.dart';
+import '../mixins/generics.dart';
+import '../visitors.dart';
+import 'constructor.dart';
+import 'expression.dart';
+import 'field.dart';
+import 'method.dart';
+import 'reference.dart';
+
+part 'extension_type.g.dart';
+
+@immutable
+abstract class ExtensionType extends Object
+    with HasAnnotations, HasDartDocs, HasGenerics
+    implements Built<ExtensionType, ExtensionTypeBuilder>, Spec {
+  factory ExtensionType([void Function(ExtensionTypeBuilder)? updates]) =
+      _$ExtensionType;
+
+  ExtensionType._();
+
+  @override
+  BuiltList<Expression> get annotations;
+
+  @override
+  BuiltList<String> get docs;
+
+  /// Whether this extension type is declared as `const`.
+  bool get constant;
+
+  String get name;
+
+  @override
+  BuiltList<Reference> get types;
+
+  /// Name of the extension type's primary constructor. An empty string
+  /// will make it unnamed.
+  String get primaryConstructorName;
+
+  RepresentationDeclaration get representationDeclaration;
+
+  BuiltList<Reference> get implements;
+
+  BuiltList<Constructor> get constructors;
+
+  BuiltList<Field> get fields;
+
+  BuiltList<Method> get methods;
+
+  @override
+  R accept<R>(
+    SpecVisitor<R> visitor, [
+    R? context,
+  ]) =>
+      visitor.visitExtensionType(this, context);
+}
+
+abstract class ExtensionTypeBuilder extends Object
+    with HasAnnotationsBuilder, HasDartDocsBuilder, HasGenericsBuilder
+    implements Builder<ExtensionType, ExtensionTypeBuilder> {
+  factory ExtensionTypeBuilder() = _$ExtensionTypeBuilder;
+
+  ExtensionTypeBuilder._();
+
+  @override
+  void update(void Function(ExtensionTypeBuilder)? updates) {
+    updates?.call(this);
+  }
+
+  @override
+  ListBuilder<Expression> annotations = ListBuilder<Expression>();
+
+  @override
+  ListBuilder<String> docs = ListBuilder<String>();
+
+  /// Whether this extension type is declared as `const`.
+  bool constant = false;
+
+  String? name;
+
+  @override
+  ListBuilder<Reference> types = ListBuilder<Reference>();
+
+  /// Name of the extension type's primary constructor. An empty string
+  /// will make it unnamed.
+  String primaryConstructorName = '';
+
+  RepresentationDeclaration? representationDeclaration;
+
+  ListBuilder<Reference> implements = ListBuilder<Reference>();
+
+  ListBuilder<Constructor> constructors = ListBuilder<Constructor>();
+
+  ListBuilder<Field> fields = ListBuilder<Field>();
+
+  ListBuilder<Method> methods = ListBuilder<Method>();
+}
+
+abstract class RepresentationDeclaration extends Object
+    with HasAnnotations, HasDartDocs
+    implements
+        Built<RepresentationDeclaration, RepresentationDeclarationBuilder> {
+  factory RepresentationDeclaration(
+          [void Function(RepresentationDeclarationBuilder)? updates]) =
+      _$RepresentationDeclaration;
+
+  RepresentationDeclaration._();
+
+  @override
+  BuiltList<Expression> get annotations;
+
+  @override
+  BuiltList<String> get docs;
+
+  Reference get declaredRepresentationType;
+
+  String get name;
+}
+
+abstract class RepresentationDeclarationBuilder extends Object
+    with HasAnnotationsBuilder, HasDartDocsBuilder
+    implements
+        Builder<RepresentationDeclaration, RepresentationDeclarationBuilder> {
+  factory RepresentationDeclarationBuilder() =
+      _$RepresentationDeclarationBuilder;
+
+  RepresentationDeclarationBuilder._();
+
+  @override
+  void update(void Function(RepresentationDeclarationBuilder)? updates) {
+    updates?.call(this);
+  }
+
+  @override
+  ListBuilder<Expression> annotations = ListBuilder<Expression>();
+
+  @override
+  ListBuilder<String> docs = ListBuilder<String>();
+
+  Reference? declaredRepresentationType;
+
+  String? name;
+}