Merge pull request #20882 from zaytsev-victor/Fixed18396

Fixed Make Method Asynchronous refactoring.

src/EditorFeatures/CSharpTest/Diagnostics/MakeMethodAsynchronous/MakeMethodAsynchronousTests.cs

@@ -684,31 +684,33 @@ async Task<int> M3Async()
         }
 
         [Theory]
-        [InlineData(0, "Task")]
-        [InlineData(1, "void", Skip = "https://github.com/dotnet/roslyn/issues/18396")]
+        [InlineData(0, "void", "Task")]
+        [InlineData(1, "void", "void")]
+        [InlineData(0, "int", "Task<int>")]
+        [InlineData(0, "Task", "Task")]
         [Trait(Traits.Feature, Traits.Features.CodeActionsMakeMethodAsynchronous)]
         [WorkItem(18307, "https://github.com/dotnet/roslyn/issues/18307")]
-        public async Task AddAsyncInLocalFunctionKeepsTrivia(int codeFixIndex, string expectedReturn)
+        public async Task AddAsyncInLocalFunctionKeepsTrivia(int codeFixIndex, string initialReturn, string expectedReturn)
         {
             await TestInRegularAndScriptAsync(
-@"using System.Threading.Tasks;
+$@"using System.Threading.Tasks;
 
 class C
-{
+{{
     public void M1()
-    {
+    {{
         // Leading trivia
-        /*1*/ void /*2*/ M2/*3*/() /*4*/
-        {
+        /*1*/ {initialReturn} /*2*/ M2/*3*/() /*4*/
+        {{
             [|await M3Async();|]
-        }
-    }
+        }}
+    }}
 
     async Task<int> M3Async()
-    {
+    {{
         return 1;
-    }
-}",
+    }}
+}}",
 $@"using System.Threading.Tasks;
 
 class C
@@ -733,7 +735,7 @@ async Task<int> M3Async()
 
         [Theory]
         [InlineData("", 0, "Task")]
-        [InlineData("", 1, "void", Skip = "https://github.com/dotnet/roslyn/issues/18396")]
+        [InlineData("", 1, "void")]
         [InlineData("public", 0, "Task")]
         [InlineData("public", 1, "void")]
         [Trait(Traits.Feature, Traits.Features.CodeActionsMakeMethodAsynchronous)]

src/Features/CSharp/Portable/MakeMethodAsynchronous/CSharpMakeMethodAsynchronousCodeFixProvider.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
-using System;
 using System.Collections.Immutable;
 using System.Composition;
 using Microsoft.CodeAnalysis.CodeFixes;
 using Microsoft.CodeAnalysis.CSharp.Extensions;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.CodeAnalysis.Formatting;
 using Microsoft.CodeAnalysis.MakeMethodAsynchronous;
 using Microsoft.CodeAnalysis.Shared.Extensions;
 
@@ -73,7 +73,7 @@ protected override bool IsAsyncSupportingFunctionSyntax(SyntaxNode node)
             bool keepVoid, IMethodSymbol methodSymbol, TypeSyntax returnType,
             INamedTypeSymbol taskType, INamedTypeSymbol taskOfTType, INamedTypeSymbol valueTaskOfTType)
         {
-            var newReturnType = returnType;
+            var newReturnType = returnType.WithAdditionalAnnotations(Formatter.Annotation);
 
             if (methodSymbol.ReturnsVoid)
             {