[wildcards] quick fix to convert UNUSED_LOCAL to wildcard

Fixes: https://github.com/dart-lang/sdk/issues/55965

Change-Id: I3585ce3823e0b7f7d2232611b27bb086b8b30d14
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/370505
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Phil Quitslund <pquitslund@google.com>

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

@@ -0,0 +1,37 @@
+// Copyright (c) 2024, 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.
+
+import 'package:analysis_server/src/services/correction/fix.dart';
+import 'package:analysis_server_plugin/edit/dart/correction_producer.dart';
+import 'package:analyzer/dart/analysis/features.dart';
+import 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer_plugin/utilities/change_builder/change_builder_core.dart';
+import 'package:analyzer_plugin/utilities/fixes/fixes.dart';
+import 'package:analyzer_plugin/utilities/range_factory.dart';
+
+class ConvertToWildcardVariable extends ResolvedCorrectionProducer {
+  ConvertToWildcardVariable({required super.context});
+
+  @override
+  CorrectionApplicability get applicability =>
+      CorrectionApplicability.singleLocation;
+
+  @override
+  FixKind get fixKind => DartFixKind.CONVERT_TO_WILDCARD_VARIABLE;
+
+  bool get wildcardVariablesEnabled =>
+      libraryElement.featureSet.isEnabled(Feature.wildcard_variables);
+
+  @override
+  Future<void> compute(ChangeBuilder builder) async {
+    if (!wildcardVariablesEnabled) return;
+
+    var node = this.node;
+    if (node is! VariableDeclaration) return;
+
+    await builder.addDartFileEdit(file, (builder) {
+      builder.addSimpleReplacement(range.token(node.name), '_');
+    });
+  }
+}

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

@@ -656,6 +656,11 @@ class DartFixKind {
     DartFixKindPriority.DEFAULT,
     'Convert to wildcard pattern',
   );
+  static const CONVERT_TO_WILDCARD_VARIABLE = FixKind(
+    'dart.fix.convert.toWildcardVariable',
+    DartFixKindPriority.DEFAULT,
+    'Convert to wildcard variable',
+  );
   static const CREATE_CLASS = FixKind(
     'dart.fix.create.class',
     DartFixKindPriority.DEFAULT,

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

@@ -77,6 +77,7 @@ import 'package:analysis_server/src/services/correction/dart/convert_to_set_lite
 import 'package:analysis_server/src/services/correction/dart/convert_to_super_parameters.dart';
 import 'package:analysis_server/src/services/correction/dart/convert_to_where_type.dart';
 import 'package:analysis_server/src/services/correction/dart/convert_to_wildcard_pattern.dart';
+import 'package:analysis_server/src/services/correction/dart/convert_to_wildcard_variable.dart';
 import 'package:analysis_server/src/services/correction/dart/create_class.dart';
 import 'package:analysis_server/src/services/correction/dart/create_constructor.dart';
 import 'package:analysis_server/src/services/correction/dart/create_constructor_for_final_fields.dart';
@@ -1696,6 +1697,7 @@ final _builtInNonLintProducers = <ErrorCode, List<ProducerGenerator>>{
   ],
   WarningCode.UNUSED_LOCAL_VARIABLE: [
     RemoveUnusedLocalVariable.new,
+    ConvertToWildcardVariable.new,
   ],
   WarningCode.UNUSED_SHOWN_NAME: [
     RemoveNameFromCombinator.new,

pkg/analysis_server/test/abstract_context.dart

@@ -66,6 +66,7 @@ class AbstractContextTest
   /// class, an empty list if there are no experiments that should be enabled.
   List<String> get experiments => [
         Feature.macros.enableString,
+        Feature.wildcard_variables.enableString,
       ];
 
   /// The path that is not in [workspaceRootPath], contains external packages.

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

@@ -0,0 +1,61 @@
+// Copyright (c) 2024, 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.
+
+import 'package:analysis_server/src/services/correction/fix.dart';
+import 'package:analyzer_plugin/utilities/fixes/fixes.dart';
+import 'package:test_reflective_loader/test_reflective_loader.dart';
+
+import 'fix_processor.dart';
+
+void main() {
+  defineReflectiveSuite(() {
+    defineReflectiveTests(ConvertToWildcardVariableTest);
+  });
+}
+
+@reflectiveTest
+class ConvertToWildcardVariableTest extends FixProcessorTest {
+  @override
+  FixKind get kind => DartFixKind.CONVERT_TO_WILDCARD_VARIABLE;
+
+  Future<void> test_convertUnusedLocalVariable() async {
+    await resolveTestCode('''
+void f() {
+  var x = '';
+}
+''');
+    await assertHasFix('''
+void f() {
+  var _ = '';
+}
+''');
+  }
+
+  Future<void> test_convertUnusedLocalVariable_list() async {
+    await resolveTestCode('''
+void f() {
+  int? x, y;
+  y;
+}
+''');
+    await assertHasFix('''
+void f() {
+  int? _, y;
+  y;
+}
+''');
+  }
+
+  Future<void> test_convertUnusedLocalVariable_preWildcards() async {
+    await resolveTestCode('''
+// @dart = 3.4
+// (pre wildcard-variables)
+
+void f() {
+  var x = '';
+}
+''');
+    await assertNoFix();
+  }
+}

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

@@ -104,6 +104,7 @@ import 'convert_to_spread_test.dart' as convert_to_spread;
 import 'convert_to_super_parameters_test.dart' as convert_to_super_parameters;
 import 'convert_to_where_type_test.dart' as convert_to_where_type;
 import 'convert_to_wildcard_pattern_test.dart' as convert_to_wildcard_pattern;
+import 'convert_to_wildcard_variable_test.dart' as convert_to_wildcard_variable;
 import 'create_class_test.dart' as create_class;
 import 'create_constructor_for_final_fields_test.dart'
     as create_constructor_for_final_field;
@@ -376,6 +377,7 @@ void main() {
     convert_to_super_parameters.main();
     convert_to_where_type.main();
     convert_to_wildcard_pattern.main();
+    convert_to_wildcard_variable.main();
     create_class.main();
     create_constructor_for_final_field.main();
     create_constructor_super.main();