Add basic extension types support

This includes allowing extension types as both methods' arguments
and return types.

Trying to mock an extension type currently silently produces a mock
of its representation, which is likely undesired, but currently
I don't see a way to detect this. It looks like constant evaluation
always produces erased types.

PiperOrigin-RevId: 610676339

Author: Ilya Yanok

CHANGELOG.md

@@ -3,6 +3,9 @@
 * Ignore "must_be_immutable" warning in generated files. Mocks cannot be made
   immutable anyway, but this way users aren't prevented from using generated
   mocks altogether.
+* Require Dart >= 3.3.0.
+* Require analyzer 6.4.1.
+* Add support for extension types.
 
 ## 5.4.4
 

lib/src/builder.dart

@@ -1631,32 +1631,33 @@ class _MockClassInfo {
   }
 
   Expression _dummyValueImplementing(
-      analyzer.InterfaceType dartType, Expression invocation) {
-    final elementToFake = dartType.element;
-    if (elementToFake is EnumElement) {
-      return _typeReference(dartType).property(
-          elementToFake.fields.firstWhere((f) => f.isEnumConstant).name);
-    } else if (elementToFake is ClassElement) {
-      if (elementToFake.isBase ||
-          elementToFake.isFinal ||
-          elementToFake.isSealed) {
-        // This class can't be faked, so try to call `dummyValue` to get
-        // a dummy value at run time.
-        // TODO(yanok): Consider checking subtypes, maybe some of them are
-        // implementable.
-        return _dummyValueFallbackToRuntime(dartType, invocation);
-      }
-      return _dummyFakedValue(dartType, invocation);
-    } else if (elementToFake is MixinElement) {
-      // This is a mixin and not a class. This should not happen in Dart 3,
-      // since it is not possible to have a value of mixin type. But we
-      // have to support this for reverse comptatibility.
-      return _dummyFakedValue(dartType, invocation);
-    } else {
-      throw StateError("Interface type '$dartType' which is nether an enum, "
-          'nor a class, nor a mixin. This case is unknown, please report a bug.');
-    }
-  }
+          analyzer.InterfaceType dartType, Expression invocation) =>
+      switch (dartType.element) {
+        EnumElement(:final fields) => _typeReference(dartType)
+            .property(fields.firstWhere((f) => f.isEnumConstant).name),
+        ClassElement() && final element
+            when element.isBase || element.isFinal || element.isSealed =>
+          // This class can't be faked, so try to call `dummyValue` to get
+          // a dummy value at run time.
+          // TODO(yanok): Consider checking subtypes, maybe some of them are
+          // implementable.
+          _dummyValueFallbackToRuntime(dartType, invocation),
+        ClassElement() => _dummyFakedValue(dartType, invocation),
+        MixinElement() =>
+          // This is a mixin and not a class. This should not happen in Dart 3,
+          // since it is not possible to have a value of mixin type. But we
+          // have to support this for reverse comptatibility.
+          _dummyFakedValue(dartType, invocation),
+        ExtensionTypeElement(:final typeErasure)
+            when !typeErasure.containsPrivateName =>
+          _dummyValue(typeErasure, invocation),
+        ExtensionTypeElement() =>
+          _dummyValueFallbackToRuntime(dartType, invocation),
+        _ => throw StateError(
+            "Interface type '$dartType' which is neither an enum, "
+            'nor a class, nor a mixin, nor an extension type. This case is '
+            'unknown, please report a bug.')
+      };
 
   /// Adds a `Fake` implementation of [elementToFake], named [fakeName].
   void _addFakeClass(String fakeName, InterfaceElement elementToFake) {

pubspec.yaml

@@ -6,10 +6,10 @@ description: >-
 repository: https://github.com/dart-lang/mockito
 
 environment:
-  sdk: ^3.1.0
+  sdk: ^3.3.0
 
 dependencies:
-  analyzer: '>=5.12.0 <7.0.0'
+  analyzer: '>=6.4.1 <7.0.0'
   build: ^2.0.0
   code_builder: ^4.5.0
   collection: ^1.15.0

test/builder/auto_mocks_test.dart

@@ -86,7 +86,7 @@ void main() {
     final packageConfig = PackageConfig([
       Package('foo', Uri.file('/foo/'),
           packageUriRoot: Uri.file('/foo/lib/'),
-          languageVersion: LanguageVersion(3, 0))
+          languageVersion: LanguageVersion(3, 3))
     ]);
     await testBuilder(buildMocks(BuilderOptions(config)), sourceAssets,
         writer: writer, outputs: outputs, packageConfig: packageConfig);
@@ -98,7 +98,7 @@ void main() {
     final packageConfig = PackageConfig([
       Package('foo', Uri.file('/foo/'),
           packageUriRoot: Uri.file('/foo/lib/'),
-          languageVersion: LanguageVersion(3, 0))
+          languageVersion: LanguageVersion(3, 3))
     ]);
 
     await testBuilder(buildMocks(BuilderOptions({})), sourceAssets,
@@ -3589,6 +3589,28 @@ void main() {
     });
   });
 
+  group('Extension types', () {
+    test('are supported as arguments', () async {
+      await expectSingleNonNullableOutput(dedent('''
+        extension type E(int v) {}
+        class Foo {
+          int m(E e);
+        }
+        '''), _containsAllOf('int m(_i2.E? e)'));
+    });
+
+    test('are supported as return types', () async {
+      await expectSingleNonNullableOutput(
+          dedent('''
+        extension type E(int v) {}
+        class Foo {
+          E get v;
+        }
+        '''),
+          decodedMatches(
+              allOf(contains('E get v'), contains('returnValue: 0'))));
+    });
+  });
   group('build_extensions support', () {
     test('should export mocks to different directory', () async {
       await testWithNonNullable({

test/builder/custom_mocks_test.dart

@@ -95,7 +95,7 @@ void main() {
     final packageConfig = PackageConfig([
       Package('foo', Uri.file('/foo/'),
           packageUriRoot: Uri.file('/foo/lib/'),
-          languageVersion: LanguageVersion(3, 0))
+          languageVersion: LanguageVersion(3, 3))
     ]);
     await testBuilder(buildMocks(BuilderOptions({})), sourceAssets,
         writer: writer, packageConfig: packageConfig);

test/end2end/foo.dart

@@ -64,3 +64,14 @@ mixin HasPrivateMixin implements HasPrivate {
   @override
   Object? _p;
 }
+
+extension type Ext(int x) {}
+
+extension type ExtOfPrivate(_Private private) {}
+
+class UsesExtTypes {
+  bool extTypeArg(Ext _) => true;
+  Ext extTypeReturn(int _) => Ext(42);
+  bool privateExtTypeArg(ExtOfPrivate _) => true;
+  ExtOfPrivate privateExtTypeReturn(int _) => ExtOfPrivate(private);
+}

test/end2end/generated_mocks_test.dart

@@ -27,8 +27,11 @@ import 'generated_mocks_test.mocks.dart';
   // ignore: deprecated_member_use_from_same_package
   MockSpec<HasPrivate>(mixingIn: [HasPrivateMixin]),
 ])
-@GenerateNiceMocks(
-    [MockSpec<Foo>(as: #MockFooNice), MockSpec<Bar>(as: #MockBarNice)])
+@GenerateNiceMocks([
+  MockSpec<Foo>(as: #MockFooNice),
+  MockSpec<Bar>(as: #MockBarNice),
+  MockSpec<UsesExtTypes>()
+])
 void main() {
   group('for a generated mock,', () {
     late MockFoo<Object> foo;
@@ -334,6 +337,35 @@ void main() {
         expect(await foo.returnsFuture(MockBar()), bar);
       });
     });
+
+    group('for a class using extension types', () {
+      late MockUsesExtTypes usesExtTypes;
+
+      setUp(() {
+        usesExtTypes = MockUsesExtTypes();
+      });
+
+      test(
+          'a method using extension type as an argument can be stubbed with any',
+          () {
+        when(usesExtTypes.extTypeArg(any)).thenReturn(true);
+        expect(usesExtTypes.extTypeArg(Ext(42)), isTrue);
+      });
+
+      test(
+          'a method using extension type as an argument can be stubbed with a '
+          'specific value', () {
+        when(usesExtTypes.extTypeArg(Ext(42))).thenReturn(true);
+        expect(usesExtTypes.extTypeArg(Ext(0)), isFalse);
+        expect(usesExtTypes.extTypeArg(Ext(42)), isTrue);
+      });
+
+      test('a method using extension type as a return type can be stubbed', () {
+        when(usesExtTypes.extTypeReturn(2)).thenReturn(Ext(42));
+        expect(usesExtTypes.extTypeReturn(2), equals(Ext(42)));
+        expect(usesExtTypes.extTypeReturn(42), equals(Ext(0)));
+      });
+    });
   });
 
   test('a generated mock can be used as a stub argument', () {