Extension type. Mark private representation fields promotable.

Change-Id: I502f82ed272856bdbd6642c06f0e54ddef4d5b01
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/330990
Reviewed-by: Brian Wilkerson <[email protected]>
Commit-Queue: Konstantin Shcheglov <[email protected]>

Author: scheglov

pkg/analyzer/lib/src/summary2/library_builder.dart

@@ -1220,6 +1220,14 @@ class _FieldPromotability extends FieldPromotability<InterfaceElement,
       for (var mixin_ in unitElement.mixins) {
         _handleMembers(addClass(mixin_, isAbstract: true), mixin_);
       }
+      // Private representation fields of extension types are always promotable.
+      // They also don't affect promotability of any other fields.
+      for (final extensionType in unitElement.extensionTypes) {
+        final representation = extensionType.representation;
+        if (representation.name.startsWith('_')) {
+          representation.isPromotable = true;
+        }
+      }
     }
 
     // Compute the set of field names that are not promotable.

pkg/analyzer/test/src/dart/resolution/field_promotion_test.dart

@@ -712,6 +712,33 @@ PrefixedIdentifier
 ''');
   }
 
+  test_extensionType_field_representation() async {
+    await assertNoErrorsInCode('''
+extension type A(int? _it) {}
+
+void f(A a) {
+  if (a._it != null) {
+    a._it;
+  }
+}
+''');
+    final node = findNode.prefixed('a._it;');
+    assertResolvedNodeText(node, r'''
+PrefixedIdentifier
+  prefix: SimpleIdentifier
+    token: a
+    staticElement: self::@function::f::@parameter::a
+    staticType: A
+  period: .
+  identifier: SimpleIdentifier
+    token: _it
+    staticElement: self::@extensionType::A::@getter::_it
+    staticType: int
+  staticElement: self::@extensionType::A::@getter::_it
+  staticType: int
+''');
+  }
+
   test_external_field() async {
     // External final fields should not be promotable.
     await assertNoErrorsInCode('''

pkg/analyzer/test/src/summary/elements_test.dart

@@ -49290,6 +49290,44 @@ library
 ''');
   }
 
+  test_isPromotable_representationField_private() async {
+    var library = await buildLibrary(r'''
+extension type A(int? _it) {}
+
+class B {
+  int _it = 0;
+}
+
+class C {
+  int get _it => 0;
+}
+''');
+
+    configuration
+      ..forPromotableFields(extensionTypeNames: {'A'})
+      ..withConstructors = false;
+    checkElementText(library, r'''
+library
+  definingUnit
+    extensionTypes
+      A @15
+        representation: self::@extensionType::A::@field::_it
+        primaryConstructor: self::@extensionType::A::@constructor::new
+        typeErasure: int?
+        interfaces
+          Object?
+        fields
+          final promotable _it @22
+            type: int?
+  fieldNameNonPromotabilityInfo
+    _it
+      conflictingFields
+        self::@class::B::@field::_it
+      conflictingGetters
+        self::@class::C::@getter::_it
+''');
+  }
+
   test_metadata() async {
     newFile('$testPackageLibPath/a.dart', r'''
 const foo = 0;
@@ -52179,6 +52217,7 @@ extension on ElementTextConfiguration {
   void forPromotableFields({
     Set<String> classNames = const {},
     Set<String> enumNames = const {},
+    Set<String> extensionTypeNames = const {},
     Set<String> mixinNames = const {},
     Set<String> fieldNames = const {},
   }) {
@@ -52189,6 +52228,8 @@ extension on ElementTextConfiguration {
         return false;
       } else if (e is EnumElement) {
         return enumNames.contains(e.name);
+      } else if (e is ExtensionTypeElement) {
+        return extensionTypeNames.contains(e.name);
       } else if (e is FieldElement) {
         return fieldNames.isEmpty || fieldNames.contains(e.name);
       } else if (e is MixinElement) {