Add a fix for HintCode.UNUSED_ELEMENT_PARAMETER.

This repurposes an existing lint CorrectionProducer to handle both
the lint and the hint.

Bug: https://github.com/dart-lang/sdk/issues/49074
Change-Id: Iacd597ca2151cdb80be9ddae0847128b4cc700a3
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/246989
Reviewed-by: Phil Quitslund <pquitslund@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Janice Collins <jcollins@google.com>

pkg/analysis_server/lib/src/services/correction/dart/remove_unused_parameter.dart

@@ -25,7 +25,15 @@ class RemoveUnusedParameter extends CorrectionProducer {
 
   @override
   Future<void> compute(ChangeBuilder builder) async {
-    var parameter = node;
+    // To work for the unused_parameter hint as well as the lint, we must
+    // allow for passing in `SimpleIdentifier`s.
+    var maybeParameter = node;
+    var maybeParameterParent = maybeParameter.parent;
+    if (maybeParameter is SimpleIdentifier && maybeParameterParent != null) {
+      maybeParameter = maybeParameterParent;
+    }
+
+    var parameter = maybeParameter;
     if (parameter is! FormalParameter) {
       return;
     }

pkg/analysis_server/lib/src/services/correction/error_fix_status.yaml

@@ -1490,7 +1490,7 @@ HintCode.UNUSED_CATCH_STACK:
 HintCode.UNUSED_ELEMENT:
   status: hasFix
 HintCode.UNUSED_ELEMENT_PARAMETER:
-  status: needsEvaluation
+  status: hasFix
 HintCode.UNUSED_FIELD:
   status: hasFix
 HintCode.UNUSED_IMPORT:

pkg/analysis_server/lib/src/services/correction/fix_internal.dart

@@ -1339,6 +1339,9 @@ class FixProcessor extends BaseProcessor {
     HintCode.UNUSED_ELEMENT: [
       RemoveUnusedElement.new,
     ],
+    HintCode.UNUSED_ELEMENT_PARAMETER: [
+      RemoveUnusedParameter.new,
+    ],
     HintCode.UNUSED_FIELD: [
       RemoveUnusedField.new,
     ],

pkg/analysis_server/test/src/services/correction/fix/remove_unused_parameter_test.dart

@@ -13,6 +13,8 @@ void main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(RemoveUnusedParameterTest);
     defineReflectiveTests(RemoveUnusedParameterBulkTest);
+    defineReflectiveTests(RemoveUnusedParameterTestHint);
+    defineReflectiveTests(RemoveUnusedParameterBulkTestHint);
   });
 }
 
@@ -37,6 +39,52 @@ class C {
   }
 }
 
+@reflectiveTest
+class RemoveUnusedParameterBulkTestHint extends BulkFixProcessorTest {
+  Future<void> test_singleFile() async {
+    await resolveTestCode('''
+class _C {
+  int? a;
+  int b;
+  int? c;
+  _C([this.a, this.b = 1, this.c]);
+}
+
+class _C2 {
+  int? a;
+  int b;
+  int? c;
+  _C2({this.a, this.b = 1, this.c});
+}
+
+void main() {
+  print(_C());
+  print(_C2());
+}
+''');
+    await assertHasFix('''
+class _C {
+  int? a;
+  int b;
+  int? c;
+  _C([this.b = 1]);
+}
+
+class _C2 {
+  int? a;
+  int b;
+  int? c;
+  _C2({this.b = 1});
+}
+
+void main() {
+  print(_C());
+  print(_C2());
+}
+''');
+  }
+}
+
 @reflectiveTest
 class RemoveUnusedParameterTest extends FixProcessorLintTest {
   @override
@@ -278,3 +326,95 @@ class C {
 ''');
   }
 }
+
+/// Situations exist where unused parameters are flagged by hints, rather
+/// than lints.   Apply the same algorithm for parameter removal as for
+/// lints.
+@reflectiveTest
+class RemoveUnusedParameterTestHint extends FixProcessorTest {
+  @override
+  FixKind get kind => DartFixKind.REMOVE_UNUSED_PARAMETER;
+
+  Future<void> test_optionalNamed() async {
+    await resolveTestCode('''
+class _C {
+  final int variable;
+  int? somethingElse;
+  _C({required this.variable, this.somethingElse});
+}
+
+void main() {
+  print(_C(variable: 123));
+}
+''');
+    await assertHasFix('''
+class _C {
+  final int variable;
+  int? somethingElse;
+  _C({required this.variable});
+}
+
+void main() {
+  print(_C(variable: 123));
+}
+''');
+  }
+
+  Future<void> test_optionalPositional() async {
+    await resolveTestCode('''
+class _C {
+  int? somethingElse;
+  int? entirely;
+  _C([this.somethingElse, this.entirely]);
+}
+
+void main() {
+  print(_C(123));
+}
+''');
+    await assertHasFix('''
+class _C {
+  int? somethingElse;
+  int? entirely;
+  _C([this.somethingElse]);
+}
+
+void main() {
+  print(_C(123));
+}
+''');
+  }
+
+  Future<void> test_optionalSuperNamed() async {
+    await resolveTestCode('''
+class B {
+  final int? key;
+  B({this.key});
+}
+
+class _C extends B {
+  final int variable;
+  _C({super.key, required this.variable});
+}
+
+void main() {
+  print(_C(variable: 123));
+}
+''');
+    await assertHasFix('''
+class B {
+  final int? key;
+  B({this.key});
+}
+
+class _C extends B {
+  final int variable;
+  _C({required this.variable});
+}
+
+void main() {
+  print(_C(variable: 123));
+}
+''');
+  }
+}