Additional tests and fixes for creating getters

Change-Id: Ia162cc49987d48c71052cba85c2d5da159c2c8f1
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/115722
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>

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

@@ -1989,7 +1989,8 @@ class FixProcessor extends BaseProcessor {
         }
       }
     } else {
-      targetElement = getEnclosingClassElement(node);
+      targetElement =
+          getEnclosingClassElement(node) ?? getEnclosingExtensionElement(node);
       if (targetElement == null) {
         return;
       }

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

@@ -232,18 +232,10 @@ String getElementQualifiedName(Element element) {
   }
 }
 
-/**
- * If the given [AstNode] is in a [ClassOrMixinDeclaration], returns the
- * [ClassElement]. Otherwise returns `null`.
- */
-ClassElement getEnclosingClassElement(AstNode node) {
-  ClassOrMixinDeclaration enclosingClassNode =
-      node.thisOrAncestorOfType<ClassOrMixinDeclaration>();
-  if (enclosingClassNode != null) {
-    return enclosingClassNode.declaredElement;
-  }
-  return null;
-}
+/// If the given [node] is in a class, enum or mixin declaration, return the
+/// declared [ClassElement]. Otherwise return `null`.
+ClassElement getEnclosingClassElement(AstNode node) =>
+    node.thisOrAncestorOfType<ClassOrMixinDeclaration>()?.declaredElement;
 
 /**
  * Returns a class or an unit member enclosing the given [node].
@@ -301,6 +293,11 @@ AstNode getEnclosingExecutableNode(AstNode node) {
   return null;
 }
 
+/// If the given [node] is in an extension, return the declared
+/// [ExtensionElement]. Otherwise return `null`.
+ExtensionElement getEnclosingExtensionElement(AstNode node) =>
+    node.thisOrAncestorOfType<ExtensionDeclaration>()?.declaredElement;
+
 /**
  * Returns [getExpressionPrecedence] for the parent of [node], or
  * ASSIGNMENT_PRECEDENCE if the parent node is a [ParenthesizedExpression].

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

@@ -373,6 +373,36 @@ class CreateGetterWithExtensionMethodsTest extends FixProcessorTest {
     super.setUp();
   }
 
+  test_internal_instance() async {
+    await resolveTestUnit('''
+extension E on String {
+  int m()  => g;
+}
+''');
+    await assertHasFix('''
+extension E on String {
+  get g => null;
+
+  int m()  => g;
+}
+''');
+  }
+
+  test_internal_static() async {
+    await resolveTestUnit('''
+extension E on String {
+  static int m()  => g;
+}
+''');
+    await assertHasFix('''
+extension E on String {
+  static get g => null;
+
+  static int m()  => g;
+}
+''');
+  }
+
   test_override() async {
     await resolveTestUnit('''
 extension E on String {