Fix unused elements when setter used

Fixes #35677

Change-Id: I2daf8b4e2cc8e1a11ed0dde730d4126154b60910
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/125620
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Samuel Rawlins <srawlins@google.com>

pkg/analyzer/lib/src/generated/resolver.dart

@@ -2089,6 +2089,7 @@ class GatherUsedLocalElementsVisitor extends RecursiveAstVisitor {
           if (element is PropertyAccessorElement && element.isSetter) {
             element = (element as PropertyAccessorElement).correspondingGetter;
           }
+          usedElements.members.add(element);
           usedElements.readMembers.add(element);
         }
       }

pkg/analyzer/test/src/diagnostics/unused_element_test.dart

@@ -402,6 +402,43 @@ main() {
 ''');
   }
 
+  test_getter_isUsed_invocation_subclass_plusPlus() async {
+    await assertNoErrorsInCode(r'''
+class A {
+  int __a = 0;
+  int get _a => __a;
+  void set _a(int val) {
+    __a = val;
+  }
+  int b() => _a++;
+}
+class B extends A {
+  @override
+  int get _a => 3;
+}
+''');
+  }
+
+  test_getter_notUsed_invocation_subclass() async {
+    await assertErrorsInCode(r'''
+class A {
+  int __a = 0;
+  int get _a => __a;
+  void set _a(int val) {
+    __a = val;
+  }
+  int b() => _a = 7;
+}
+class B extends A {
+  @override
+  int get _a => 3;
+}
+''', [
+      error(HintCode.UNUSED_ELEMENT, 35, 2),
+      error(HintCode.UNUSED_ELEMENT, 155, 2),
+    ]);
+  }
+
   test_getter_notUsed_noReference() async {
     await assertErrorsInCode(r'''
 class A {

pkg/compiler/lib/src/js_backend/field_naming_mixin.dart

@@ -106,8 +106,6 @@ class _FieldNamingScope {
   /// The number of locally used fields. Depending on the naming source
   /// (e.g. inheritance based or globally unique for mixixns) this
   /// might be different from [inheritanceBasedFieldNameCounter].
-  // TODO(35677): remove
-  // ignore: unused_element
   int get _localFieldNameCounter => _fieldNameCounter;
   void set _localFieldNameCounter(int val) {
     _fieldNameCounter = val;
@@ -192,8 +190,6 @@ class _FieldNamingScope {
 /// in generated names themselves.
 class _MixinFieldNamingScope extends _FieldNamingScope {
   @override
-  // TODO(35677): remove
-  // ignore: unused_element
   int get _localFieldNameCounter => registry.globalCount;
   @override
   void set _localFieldNameCounter(int val) {