Update SA1015 to require trailing space after an explicit generic return type in a lambda expression

#3624

Author: bjornhellander

StyleCop.Analyzers/StyleCop.Analyzers.Test.CSharp10/SpacingRules/SA1015CSharp10UnitTests.cs

@@ -3,9 +3,42 @@
 
 namespace StyleCop.Analyzers.Test.CSharp10.SpacingRules
 {
+    using System.Threading;
+    using System.Threading.Tasks;
+    using Microsoft.CodeAnalysis.Testing;
     using StyleCop.Analyzers.Test.CSharp9.SpacingRules;
+    using Xunit;
+    using static StyleCop.Analyzers.Test.Verifiers.StyleCopCodeFixVerifier<
+        StyleCop.Analyzers.SpacingRules.SA1015ClosingGenericBracketsMustBeSpacedCorrectly,
+        StyleCop.Analyzers.SpacingRules.TokenSpacingCodeFixProvider>;
 
     public class SA1015CSharp10UnitTests : SA1015CSharp9UnitTests
     {
+        [Fact]
+        [WorkItem(3624, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3624")]
+        public async Task TestLambdaWithExplicitGenericReturnTypeAsync()
+        {
+            const string testCode = @"using System.Threading.Tasks;
+
+public class TestClass
+{
+    public void TestMethod()
+    {
+        var _ = Task<int[|>|](int x) => Task.FromResult(x);
+    }
+}";
+
+            const string fixedCode = @"using System.Threading.Tasks;
+
+public class TestClass
+{
+    public void TestMethod()
+    {
+        var _ = Task<int> (int x) => Task.FromResult(x);
+    }
+}";
+
+            await VerifyCSharpFixAsync(testCode, DiagnosticResult.EmptyDiagnosticResults, fixedCode, CancellationToken.None).ConfigureAwait(false);
+        }
     }
 }

StyleCop.Analyzers/StyleCop.Analyzers/SpacingRules/SA1015ClosingGenericBracketsMustBeSpacedCorrectly.cs

@@ -108,7 +108,6 @@ private static void HandleGreaterThanToken(SyntaxTreeAnalysisContext context, Sy
                 SyntaxToken nextToken = token.GetNextToken();
                 switch (nextToken.Kind())
                 {
-                case SyntaxKind.OpenParenToken:
                 // DotToken isn't listed above, but it's required for reasonable member access formatting
                 case SyntaxKind.DotToken:
                 // CommaToken isn't listed above, but it's required for reasonable nested generic type arguments formatting
@@ -122,6 +121,10 @@ private static void HandleGreaterThanToken(SyntaxTreeAnalysisContext context, Sy
                     allowTrailingSpace = false;
                     break;
 
+                case SyntaxKind.OpenParenToken:
+                    AnalyzeWithTrailingOpenParen(nextToken, out allowTrailingNoSpace, out allowTrailingSpace);
+                    break;
+
                 case SyntaxKind.CloseParenToken:
                 case SyntaxKind.GreaterThanToken:
                     allowTrailingNoSpace = true;
@@ -187,5 +190,33 @@ private static void HandleGreaterThanToken(SyntaxTreeAnalysisContext context, Sy
                 }
             }
         }
+
+        private static void AnalyzeWithTrailingOpenParen(
+            SyntaxToken nextToken,
+            out bool allowTrailingNoSpace,
+            out bool allowTrailingSpace)
+        {
+            switch (nextToken.Parent.Kind())
+            {
+            // List<int> (int x) => new List<int> { x }
+            //         ^ ^
+            case SyntaxKind.ParameterList when nextToken.Parent.Parent.IsKind(SyntaxKind.ParenthesizedLambdaExpression):
+                allowTrailingNoSpace = false;
+                allowTrailingSpace = true;
+                break;
+
+            // NOTE: Intentionally keeping redundant cases here as documentation of what is known to occur
+            // M<int>()
+            //      ^^
+            case SyntaxKind.ArgumentList:
+            // void M<T>(T x) { }
+            //         ^^
+            case SyntaxKind.ParameterList when nextToken.Parent.Parent.IsKind(SyntaxKind.MethodDeclaration):
+            default:
+                allowTrailingNoSpace = true;
+                allowTrailingSpace = false;
+                break;
+            }
+        }
     }
 }