Issue 28261. Add support for implementing generic methods in Quick Fix.

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

Index: pkg/analysis_server/lib/src/services/correction/fix_internal.dart
diff --git a/pkg/analysis_server/lib/src/services/correction/fix_internal.dart b/pkg/analysis_server/lib/src/services/correction/fix_internal.dart
index efec5eeb46118204359679ef9dace81dfcec3234..be1083c5f4ee83418601452d33c93735b028e190 100644
--- a/pkg/analysis_server/lib/src/services/correction/fix_internal.dart
+++ b/pkg/analysis_server/lib/src/services/correction/fix_internal.dart
@@ -1365,6 +1365,7 @@ class FixProcessor {
 
   void _addFix_createMissingOverrides_single(SourceBuilder sb,
       ClassDeclaration targetClass, ExecutableElement element) {
+    utils.targetExecutableElement = element;
     // prepare environment
     String prefix = utils.getIndent(1);
     String prefix2 = utils.getIndent(2);
@@ -1400,6 +1401,17 @@ class FixProcessor {
     }
     // name
     sb.append(element.displayName);
+    // type parameters
+    {
+      List<TypeParameterElement> typeParameters = element.typeParameters;
+      if (typeParameters.isNotEmpty) {
+        sb.append('<');
+        for (TypeParameterElement typeParameter in typeParameters) {
+          _appendTypeParameter(sb, typeParameter);
+        }
+        sb.append('>');
+      }
+    }
     // parameters + body
     if (isGetter) {
       sb.append(' => null;');
@@ -1417,6 +1429,7 @@ class FixProcessor {
       sb.append('}');
     }
     sb.append(eol);
+    utils.targetExecutableElement = null;
   }
 
   void _addFix_createNoSuchMethod() {
@@ -2534,7 +2547,7 @@ class FixProcessor {
   }
 
   void _appendType(SourceBuilder sb, DartType type,
-      {String groupId, bool orVar: false}) {
+      {String groupId, bool orVar: false, bool trailingSpace: true}) {
     if (type != null && !type.isDynamic) {
       String typeSource = utils.getTypeSource(type, librariesToImport);
       if (groupId != null) {
@@ -2544,12 +2557,23 @@ class FixProcessor {
       } else {
         sb.append(typeSource);
       }
-      sb.append(' ');
+      if (trailingSpace) {
+        sb.append(' ');
+      }
     } else if (orVar) {
       sb.append('var ');
     }
   }
 
+  void _appendTypeParameter(
+      SourceBuilder sb, TypeParameterElement typeParameter) {
+    sb.append(typeParameter.name);
+    if (typeParameter.bound != null) {
+      sb.append(' extends ');
+      _appendType(sb, typeParameter.bound, trailingSpace: false);
+    }
+  }
+
   /**
    * Computes the name of the library at the given [path].
    * See https://www.dartlang.org/articles/style-guide/#names for conventions.