Add extension type support for create method fix

Bug:49741
Change-Id: I8687dbf3fe0532bd04163a42104bbdddd0d173fb
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/331742
Commit-Queue: Keerti Parthasarathy <keertip@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>

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

@@ -339,6 +339,17 @@ abstract class ResolvedCorrectionProducer
     return null;
   }
 
+  /// Return the extension type for the given [element].
+  Future<ExtensionTypeDeclaration?> getExtensionTypeDeclaration(
+      ExtensionTypeElement element) async {
+    var result = await sessionHelper.getElementDeclaration(element);
+    var node = result?.node;
+    if (node is ExtensionTypeDeclaration) {
+      return node;
+    }
+    return null;
+  }
+
   LinterContext getLinterContext(path.Context pathContext) {
     return LinterContextImpl(
       [], // unused

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

@@ -160,13 +160,16 @@ class CreateMethod extends ResolvedCorrectionProducer {
         targetNode = await getMixinDeclaration(targetClassElement);
       } else if (targetClassElement is ClassElement) {
         targetNode = await getClassDeclaration(targetClassElement);
+      } else if (targetClassElement is ExtensionTypeElement) {
+        targetNode = await getExtensionTypeDeclaration(targetClassElement);
       }
       if (targetNode == null) {
         return;
       }
       // maybe static
       if (target is Identifier) {
-        staticModifier = target.staticElement?.kind == ElementKind.CLASS;
+        staticModifier = target.staticElement?.kind == ElementKind.CLASS ||
+            target.staticElement?.kind == ElementKind.EXTENSION_TYPE;
       }
       // use different utils
       var targetPath = targetClassElement.source.fullName;

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

@@ -263,6 +263,24 @@ void f() {
 ''');
   }
 
+  Future<void> test_createQualified_fromExtensionType() async {
+    await resolveTestCode('''
+extension type A(String s) {
+}
+void f() {
+  A.myUndefinedMethod();
+}
+''');
+    await assertHasFix('''
+extension type A(String s) {
+  static void myUndefinedMethod() {}
+}
+void f() {
+  A.myUndefinedMethod();
+}
+''');
+  }
+
   Future<void> test_createQualified_fromInstance() async {
     await resolveTestCode('''
 class A {
@@ -281,6 +299,24 @@ void f(A a) {
 ''');
   }
 
+  Future<void> test_createQualified_instance_fromExtensionType() async {
+    await resolveTestCode('''
+extension type A(String s) {
+}
+void f(A a) {
+  a.myUndefinedMethod();
+}
+''');
+    await assertHasFix('''
+extension type A(String s) {
+  void myUndefinedMethod() {}
+}
+void f(A a) {
+  a.myUndefinedMethod();
+}
+''');
+  }
+
   Future<void> test_createQualified_targetIsFunctionType() async {
     await resolveTestCode('''
 typedef A();