Hide nonVirtual elements in override completions.

Fixes https://github.com/dart-lang/sdk/issues/55628

Change-Id: I70dcf5b47dae2faef30a47a4e3f811e735a1eeec
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/371742
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Keerti Parthasarathy <keertip@google.com>

pkg/analysis_server/lib/src/services/completion/dart/override_helper.dart

@@ -43,6 +43,10 @@ class OverrideHelper {
       var element = interfaceMap[name];
       // Gracefully degrade if the overridden element has not been resolved.
       if (element != null) {
+        if (_hasNonVirtualAnnotation(element)) {
+          continue;
+        }
+
         var invokeSuper = interface.isSuperImplemented(name);
         var matcherScore = math.max(
             math.max(state.matcher.score('override'),
@@ -63,6 +67,17 @@ class OverrideHelper {
     }
   }
 
+  /// Checks if the [element] has the `@nonVirtual` annotation.
+  bool _hasNonVirtualAnnotation(ExecutableElement element) {
+    if (element is PropertyAccessorElement && element.isSynthetic) {
+      var variable = element.variable2;
+      if (variable != null && variable.hasNonVirtual) {
+        return true;
+      }
+    }
+    return element.hasNonVirtual;
+  }
+
   /// Return the list of names that belong to the [interface] of a class, but
   /// are not yet declared in the class.
   List<Name> _namesToOverride(Uri libraryUri, Interface interface) {

pkg/analysis_server/test/services/completion/dart/location/class_body_test.dart

@@ -644,6 +644,7 @@ mixin OverrideTestCases on AbstractCompletionDriverTest {
   @override
   Future<void> setUp() async {
     await super.setUp();
+    writeTestPackageConfig(meta: true);
 
     printerConfiguration = printer.Configuration(
       filter: (suggestion) {
@@ -1236,6 +1237,37 @@ class A {
   void foo01() {}
 }
 
+class B extends A {
+  @override
+  foo^
+}
+''');
+
+    assertResponse(r'''
+replacement
+  left: 3
+suggestions
+  void foo01() {
+    // TODO: implement foo01
+    super.foo01();
+  }
+    kind: override
+    displayText: foo01() { … }
+    selection: 48 14
+''');
+  }
+
+  Future<void> test_class_method_fromExtends_withOverride_nonVirtual() async {
+    await computeSuggestions('''
+import 'package:meta/meta.dart';
+
+class A {
+  void foo01() {}
+
+  @nonVirtual
+  void foo02() {}
+}
+
 class B extends A {
   @override
   foo^