remove redundant @required annotations when adding required

Fixes: https://github.com/dart-lang/sdk/issues/43603

Change-Id: I21ccee4787695b72d5ac25195ade638e918d9550
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/171420
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Phil Quitslund <pquitslund@google.com>

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

@@ -4,6 +4,8 @@
 
 import 'package:analysis_server/src/services/correction/dart/abstract_producer.dart';
 import 'package:analysis_server/src/services/correction/fix.dart';
+import 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/source/source_range.dart';
 import 'package:analyzer_plugin/utilities/change_builder/change_builder_core.dart';
 import 'package:analyzer_plugin/utilities/fixes/fixes.dart';
 
@@ -14,7 +16,25 @@ class AddRequiredKeyword extends CorrectionProducer {
   @override
   Future<void> compute(ChangeBuilder builder) async {
     await builder.addDartFileEdit(file, (builder) {
-      builder.addSimpleInsertion(node.parent.offset, 'required ');
+      var insertOffset = node.parent.offset;
+
+      var parent = node.parent;
+      if (parent is FormalParameter) {
+        var metadata = parent.metadata;
+        // Check for redundant `@required` annotations.
+        if (metadata.isNotEmpty) {
+          for (var annotation in metadata) {
+            if (annotation.elementAnnotation.isRequired) {
+              var length = annotation.endToken.next.offset -
+                  annotation.beginToken.offset;
+              builder.addDeletion(SourceRange(annotation.offset, length));
+              break;
+            }
+          }
+          insertOffset = metadata.endToken.next.offset;
+        }
+      }
+      builder.addSimpleInsertion(insertOffset, 'required ');
     });
   }
 

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

@@ -45,11 +45,131 @@ class AddRequiredWithNullSafetyTest extends FixProcessorTest
   @override
   FixKind get kind => DartFixKind.ADD_REQUIRED2;
 
-  Future<void> test_withAssert() async {
+  Future<void> test_nonNullable() async {
     await resolveTestCode('''
 void function({String param}) {}
 ''');
     await assertHasFix('''
+void function({required String param}) {}
+''');
+  }
+
+  Future<void> test_withRequiredAnnotation() async {
+    writeTestPackageConfig(meta: true);
+
+    await resolveTestCode('''
+import 'package:meta/meta.dart';
+
+void function({@required String param}) {}
+''');
+    await assertHasFix('''
+import 'package:meta/meta.dart';
+
+void function({required String param}) {}
+''');
+  }
+
+  Future<void> test_withRequiredAnnotation_constructor() async {
+    writeTestPackageConfig(meta: true);
+
+    await resolveTestCode('''
+import 'package:meta/meta.dart';
+
+class A {
+  String foo;
+  A({@required this.foo});
+}
+''');
+    await assertHasFix('''
+import 'package:meta/meta.dart';
+
+class A {
+  String foo;
+  A({required this.foo});
+}
+''');
+  }
+
+  Future<void> test_withRequiredAnnotation_functionParam() async {
+    writeTestPackageConfig(meta: true);
+
+    await resolveTestCode('''
+import 'package:meta/meta.dart';
+
+void f({@required int g(String)}) { }
+''');
+    await assertHasFix('''
+import 'package:meta/meta.dart';
+
+void f({required int g(String)}) { }
+''');
+  }
+
+  Future<void> test_withRequiredAnnotationInList_first() async {
+    writeTestPackageConfig(meta: true);
+
+    await resolveTestCode('''
+import 'package:meta/meta.dart';
+
+class Foo {
+  const Foo();
+}
+
+const foo = Foo();
+
+void function({@required @foo String param}) {}
+''');
+    await assertHasFix('''
+import 'package:meta/meta.dart';
+
+class Foo {
+  const Foo();
+}
+
+const foo = Foo();
+
+void function({@foo required String param}) {}
+''');
+  }
+
+  Future<void> test_withRequiredAnnotationInList_last() async {
+    writeTestPackageConfig(meta: true);
+
+    await resolveTestCode('''
+import 'package:meta/meta.dart';
+
+class Foo {
+  const Foo();
+}
+
+const foo = Foo();
+
+void function({@foo @required String param}) {}
+''');
+    await assertHasFix('''
+import 'package:meta/meta.dart';
+
+class Foo {
+  const Foo();
+}
+
+const foo = Foo();
+
+void function({@foo required String param}) {}
+''');
+  }
+
+  Future<void> test_withRequiredAnnotationWithReason() async {
+    writeTestPackageConfig(meta: true);
+
+    await resolveTestCode('''
+import 'package:meta/meta.dart';
+
+void function({@Required('reason') String param}) {}
+''');
+    await assertHasFix('''
+import 'package:meta/meta.dart';
+
 void function({required String param}) {}
 ''');
   }