[cfe] Allow mixins in enums

Part of #47453

Change-Id: I04d0a7690b6619ca61f364da756917319e6081b8
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/227541
Reviewed-by: Johnni Winther <[email protected]>
Commit-Queue: Chloe Stefantsova <[email protected]>

Author: chloestefantsova

pkg/front_end/lib/src/fasta/source/diet_listener.dart

@@ -50,6 +50,8 @@ import '../type_inference/type_inference_engine.dart'
     show InferenceDataForTesting, TypeInferenceEngine;
 import '../type_inference/type_inferrer.dart' show TypeInferrer;
 import 'diet_parser.dart';
+import 'source_constructor_builder.dart';
+import 'source_enum_builder.dart';
 import 'source_field_builder.dart';
 import 'source_function_builder.dart';
 import 'source_library_builder.dart' show SourceLibraryBuilder;
@@ -962,6 +964,19 @@ class DietListener extends StackListenerImpl {
   void endEnum(Token enumKeyword, Token leftBrace, int memberCount) {
     debugEvent("Enum");
     checkEmpty(enumKeyword.charOffset);
+
+    SourceEnumBuilder? enumBuilder = currentClass as SourceEnumBuilder?;
+    if (enumBuilder != null) {
+      DeclaredSourceConstructorBuilder? defaultConstructorBuilder =
+          enumBuilder.synthesizedDefaultConstructorBuilder;
+      if (defaultConstructorBuilder != null) {
+        BodyBuilder bodyBuilder =
+            createFunctionListener(defaultConstructorBuilder);
+        bodyBuilder.finishConstructor(
+            defaultConstructorBuilder, AsyncMarker.Sync, new EmptyStatement());
+      }
+    }
+
     currentDeclaration = null;
     memberScope = libraryBuilder.scope;
   }

pkg/front_end/lib/src/fasta/source/outline_builder.dart

@@ -2329,7 +2329,7 @@ class OutlineBuilder extends StackListenerImpl {
 
     // We pop more values than needed to reach typeVariables, offset and name.
     List<TypeBuilder>? interfaces = pop() as List<TypeBuilder>?;
-    List<TypeBuilder>? mixins = pop() as List<TypeBuilder>?;
+    Object? mixins = pop();
     List<TypeVariableBuilder>? typeVariables =
         pop() as List<TypeVariableBuilder>?;
     int charOffset = popCharOffset(); // identifier char offset.
@@ -2341,7 +2341,7 @@ class OutlineBuilder extends StackListenerImpl {
     push(name ?? NullValue.Name);
     push(charOffset);
     push(typeVariables ?? NullValue.TypeVariables);
-    push(mixins ?? NullValue.TypeBuilderList);
+    push(mixins ?? NullValue.TypeBuilder);
     push(interfaces ?? NullValue.TypeBuilderList);
 
     push(enumKeyword.charOffset); // start char offset.
@@ -2364,7 +2364,7 @@ class OutlineBuilder extends StackListenerImpl {
     int endCharOffset = popCharOffset();
     int startCharOffset = popCharOffset();
     pop() as List<TypeBuilder>?; // interfaces.
-    pop() as List<TypeBuilder>?; // mixins.
+    MixinApplicationBuilder? mixinBuilder = pop() as MixinApplicationBuilder?;
     List<TypeVariableBuilder>? typeVariables =
         pop() as List<TypeVariableBuilder>?;
     int charOffset = popCharOffset(); // identifier char offset.
@@ -2373,8 +2373,15 @@ class OutlineBuilder extends StackListenerImpl {
     checkEmpty(startCharOffset);
 
     if (name is! ParserRecovery) {
-      libraryBuilder.addEnum(metadata, name as String, typeVariables,
-          enumConstantInfos, startCharOffset, charOffset, endCharOffset);
+      libraryBuilder.addEnum(
+          metadata,
+          name as String,
+          typeVariables,
+          mixinBuilder,
+          enumConstantInfos,
+          startCharOffset,
+          charOffset,
+          endCharOffset);
     } else {
       libraryBuilder
           .endNestedDeclaration(
@@ -3199,15 +3206,23 @@ class OutlineBuilder extends StackListenerImpl {
     if (mixins is ParserRecovery) {
       push(new ParserRecovery(withKeyword.charOffset));
     } else {
-      // TODO(cstefantsova): Handle enum mixins here.
-      push(mixins);
+      NamedTypeBuilder enumType = new NamedTypeBuilder(
+          "_Enum",
+          const NullabilityBuilder.omitted(),
+          /* arguments = */ null,
+          /* fileUri = */ null,
+          /* charOffset = */ null,
+          instanceTypeVariableAccess:
+              InstanceTypeVariableAccessState.Unexpected);
+      push(libraryBuilder.addMixinApplication(
+          enumType, mixins as List<TypeBuilder>, withKeyword.charOffset));
     }
   }
 
   @override
   void handleEnumNoWithClause() {
     debugEvent("EnumNoWithClause");
-    push(NullValue.TypeBuilderList);
+    push(NullValue.TypeBuilder);
   }
 
   @override

pkg/front_end/lib/src/fasta/source/source_class_builder.dart

@@ -105,6 +105,8 @@ class SourceClassBuilder extends ClassBuilderImpl
 
   SourceClassBuilder? _patchBuilder;
 
+  final bool isEnumMixin;
+
   SourceClassBuilder(
       List<MetadataBuilder>? metadata,
       int modifiers,
@@ -124,7 +126,8 @@ class SourceClassBuilder extends ClassBuilderImpl
       {Class? cls,
       this.mixedInTypeBuilder,
       this.isMixinDeclaration = false,
-      this.isMacro: false})
+      this.isMacro: false,
+      this.isEnumMixin: false})
       : actualCls = initializeClass(cls, typeVariables, name, parent,
             startCharOffset, nameOffset, charEndOffset, referencesFromIndexed),
         super(metadata, modifiers, name, typeVariables, supertype, interfaces,
@@ -195,6 +198,11 @@ class SourceClassBuilder extends ClassBuilderImpl
     if (supertypeBuilder != null) {
       supertypeBuilder = _checkSupertype(supertypeBuilder!);
     }
+    if (isEnumMixin) {
+      assert(supertypeBuilder?.name == "_Enum");
+      supertypeBuilder?.resolveIn(coreLibrary.scope,
+          supertypeBuilder?.charOffset ?? charOffset, fileUri, library);
+    }
     Supertype? supertype =
         supertypeBuilder?.buildSupertype(library, charOffset, fileUri);
     if (supertype != null) {

pkg/front_end/lib/src/fasta/source/source_enum_builder.dart

@@ -46,6 +46,7 @@ import '../builder/named_type_builder.dart';
 import '../builder/nullability_builder.dart';
 import '../builder/procedure_builder.dart';
 import '../builder/type_builder.dart';
+import '../builder/type_declaration_builder.dart';
 import '../builder/type_variable_builder.dart';
 import '../fasta_codes.dart'
     show
@@ -86,7 +87,7 @@ class SourceEnumBuilder extends SourceClassBuilder {
 
   final NamedTypeBuilder listType;
 
-  DeclaredSourceConstructorBuilder? _synthesizedDefaultConstructorBuilder;
+  DeclaredSourceConstructorBuilder? synthesizedDefaultConstructorBuilder;
 
   SourceEnumBuilder.internal(
       List<MetadataBuilder>? metadata,
@@ -99,7 +100,7 @@ class SourceEnumBuilder extends SourceClassBuilder {
       this.intType,
       this.listType,
       this.objectType,
-      TypeBuilder enumType,
+      TypeBuilder supertypeBuilder,
       this.stringType,
       SourceLibraryBuilder parent,
       int startCharOffset,
@@ -111,7 +112,7 @@ class SourceEnumBuilder extends SourceClassBuilder {
             0,
             name,
             typeVariables,
-            enumType,
+            supertypeBuilder,
             /* interfaces = */ null,
             /* onTypes = */ null,
             scope,
@@ -128,6 +129,7 @@ class SourceEnumBuilder extends SourceClassBuilder {
       List<MetadataBuilder>? metadata,
       String name,
       List<TypeVariableBuilder>? typeVariables,
+      TypeBuilder? supertypeBuilder,
       List<EnumConstantInfo?>? enumConstantInfos,
       SourceLibraryBuilder parent,
       int startCharOffset,
@@ -173,7 +175,7 @@ class SourceEnumBuilder extends SourceClassBuilder {
         /* fileUri = */ null,
         /* charOffset = */ null,
         instanceTypeVariableAccess: InstanceTypeVariableAccessState.Unexpected);
-    NamedTypeBuilder enumType = new NamedTypeBuilder(
+    supertypeBuilder ??= new NamedTypeBuilder(
         "_Enum",
         const NullabilityBuilder.omitted(),
         /* arguments = */ null,
@@ -418,14 +420,14 @@ class SourceEnumBuilder extends SourceClassBuilder {
         intType,
         listType,
         objectType,
-        enumType,
+        supertypeBuilder,
         stringType,
         parent,
         startCharOffsetComputed,
         charOffset,
         charEndOffset,
         referencesFromIndexed)
-      .._synthesizedDefaultConstructorBuilder =
+      ..synthesizedDefaultConstructorBuilder =
           synthesizedDefaultConstructorBuilder;
 
     void setParent(String name, MemberBuilder? builder) {
@@ -458,9 +460,21 @@ class SourceEnumBuilder extends SourceClassBuilder {
         coreLibrary.scope, charOffset, fileUri, libraryBuilder);
     objectType.resolveIn(
         coreLibrary.scope, charOffset, fileUri, libraryBuilder);
-    TypeBuilder supertypeBuilder = this.supertypeBuilder!;
-    supertypeBuilder.resolveIn(
-        coreLibrary.scope, charOffset, fileUri, libraryBuilder);
+    TypeBuilder? supertypeBuilder = this.supertypeBuilder;
+    NamedTypeBuilder? enumType;
+
+    while (enumType == null && supertypeBuilder is NamedTypeBuilder) {
+      TypeDeclarationBuilder? superclassBuilder = supertypeBuilder.declaration;
+      if (superclassBuilder is ClassBuilder &&
+          superclassBuilder.isMixinApplication) {
+        supertypeBuilder = superclassBuilder.supertypeBuilder;
+      } else {
+        enumType = supertypeBuilder;
+      }
+    }
+    assert(enumType is NamedTypeBuilder && enumType.name == "_Enum");
+    enumType!.resolveIn(coreLibrary.scope, charOffset, fileUri, libraryBuilder);
+
     listType.resolveIn(coreLibrary.scope, charOffset, fileUri, libraryBuilder);
 
     List<Expression> values = <Expression>[];
@@ -481,34 +495,39 @@ class SourceEnumBuilder extends SourceClassBuilder {
     valuesBuilder.build(libraryBuilder);
 
     // The super initializer for the synthesized default constructor is
-    // inserted here. Other constructors are handled in
-    // [BodyBuilder.finishConstructor], as they are processed via the pipeline
-    // for constructor parsing and building.
-    if (_synthesizedDefaultConstructorBuilder != null) {
-      Constructor constructor =
-          _synthesizedDefaultConstructorBuilder!.build(libraryBuilder);
-      ClassBuilder objectClass = objectType.declaration as ClassBuilder;
-      ClassBuilder enumClass = supertypeBuilder.declaration as ClassBuilder;
-      MemberBuilder? superConstructor = enumClass.findConstructorOrFactory(
-          "", charOffset, fileUri, libraryBuilder);
-      if (superConstructor == null || !superConstructor.isConstructor) {
-        // TODO(ahe): Ideally, we would also want to check that [Object]'s
-        // unnamed constructor requires no arguments. But that information
-        // isn't always available at this point, and it's not really a
-        // situation that can happen unless you start modifying the SDK
-        // sources. (We should add a correct message. We no longer depend on
-        // Object here.)
-        library.addProblem(
-            messageNoUnnamedConstructorInObject,
-            objectClass.charOffset,
-            objectClass.name.length,
-            objectClass.fileUri);
-      } else {
-        constructor.initializers.add(new SuperInitializer(
-            superConstructor.member as Constructor,
-            new Arguments.forwarded(
-                constructor.function, libraryBuilder.library))
-          ..parent = constructor);
+    // inserted here if the enum's supertype is _Enum to preserve the legacy
+    // behavior or having the old-style enum constants built in the outlines.
+    // Other constructors are handled in [BodyBuilder.finishConstructor] as
+    // they are processed via the pipeline for constructor parsing and
+    // building.
+    if (identical(this.supertypeBuilder, enumType)) {
+      if (synthesizedDefaultConstructorBuilder != null) {
+        Constructor constructor =
+            synthesizedDefaultConstructorBuilder!.build(libraryBuilder);
+        ClassBuilder objectClass = objectType.declaration as ClassBuilder;
+        ClassBuilder enumClass = enumType.declaration as ClassBuilder;
+        MemberBuilder? superConstructor = enumClass.findConstructorOrFactory(
+            "", charOffset, fileUri, libraryBuilder);
+        if (superConstructor == null || !superConstructor.isConstructor) {
+          // TODO(ahe): Ideally, we would also want to check that [Object]'s
+          // unnamed constructor requires no arguments. But that information
+          // isn't always available at this point, and it's not really a
+          // situation that can happen unless you start modifying the SDK
+          // sources. (We should add a correct message. We no longer depend on
+          // Object here.)
+          library.addProblem(
+              messageNoUnnamedConstructorInObject,
+              objectClass.charOffset,
+              objectClass.name.length,
+              objectClass.fileUri);
+        } else {
+          constructor.initializers.add(new SuperInitializer(
+              superConstructor.member as Constructor,
+              new Arguments.forwarded(
+                  constructor.function, libraryBuilder.library))
+            ..parent = constructor);
+        }
+        synthesizedDefaultConstructorBuilder = null;
       }
     }
 

pkg/front_end/lib/src/fasta/source/source_library_builder.dart

@@ -2103,7 +2103,8 @@ class SourceLibraryBuilder extends LibraryBuilderImpl {
       List<TypeVariableBuilder>? typeVariables,
       int modifiers: 0,
       List<TypeBuilder>? interfaces,
-      required bool isMacro}) {
+      required bool isMacro,
+      bool isEnumMixin: false}) {
     if (name == null) {
       // The following parameters should only be used when building a named
       // mixin application.
@@ -2322,7 +2323,8 @@ class SourceLibraryBuilder extends LibraryBuilderImpl {
             charEndOffset,
             referencesFromIndexedClass,
             mixedInTypeBuilder: isMixinDeclaration ? null : mixin,
-            isMacro: isNamedMixinApplication && isMacro);
+            isMacro: isNamedMixinApplication && isMacro,
+            isEnumMixin: isEnumMixin && i == 0);
         // TODO(ahe, kmillikin): Should always be true?
         // pkg/analyzer/test/src/summary/resynthesize_kernel_test.dart can't
         // handle that :(
@@ -2791,6 +2793,7 @@ class SourceLibraryBuilder extends LibraryBuilderImpl {
       List<MetadataBuilder>? metadata,
       String name,
       List<TypeVariableBuilder>? typeVariables,
+      TypeBuilder? supertypeBuilder,
       List<EnumConstantInfo?>? enumConstantInfos,
       int startCharOffset,
       int charOffset,
@@ -2812,6 +2815,9 @@ class SourceLibraryBuilder extends LibraryBuilderImpl {
         metadata,
         name,
         typeVariables,
+        applyMixins(supertypeBuilder, startCharOffset, charOffset,
+            charEndOffset, name, /* isMixinDeclaration = */ false,
+            typeVariables: typeVariables, isMacro: false, isEnumMixin: true),
         enumConstantInfos,
         this,
         startCharOffset,

pkg/front_end/test/spell_checking_list_common.txt

@@ -1029,6 +1029,7 @@ entity's
 entries
 entry
 enum
+enum's
 enumerated
 enumeration
 enumerations

pkg/front_end/testcases/enhanced_enums/simple_mixins.dart

@@ -0,0 +1,51 @@
+// Copyright (c) 2022, 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.
+
+class A {
+  String get foo => "foo";
+}
+
+class B {
+  int bar() => 42;
+}
+
+mixin M {
+  void set callOnAssignment(void Function() f) {
+    f();
+  }
+}
+
+enum E1 with A { one, two }
+
+enum E2 with A, B { one, two }
+
+enum E3 with M { one, two }
+
+expectEquals(x, y) {
+  if (x != y) {
+    throw "Expected '$x' and '$y' to be equal.";
+  }
+}
+
+expectThrows(void Function() f) {
+  try {
+    f();
+    throw "Expected function to throw.";
+  } catch (e) {}
+}
+
+void throwOnCall() {
+  throw 42;
+}
+
+main() {
+  expectEquals(E1.one.foo, "foo");
+  expectEquals(E1.two.foo, "foo");
+  expectEquals(E2.one.foo, "foo");
+  expectEquals(E2.two.foo, "foo");
+  expectEquals(E2.one.bar(), "bar");
+  expectEquals(E2.two.bar(), "bar");
+  expectThrows(E3.one.callOnAssignment = throwOnCall);
+  expectThrows(E3.two.callOnAssignment = throwOnCall);
+}