Fixed spacing issue for SA1139 code fix

Author: vweijsters

StyleCop.Analyzers/StyleCop.Analyzers.CodeFixes/ReadabilityRules/SA1139CodeFixProvider.cs

@@ -47,7 +47,6 @@ public override Task RegisterCodeFixesAsync(CodeFixContext context)
         private static async Task<Document> GetTransformedDocumentAsync(Document document, Diagnostic diagnostic, CancellationToken cancellationToken)
         {
             var syntaxRoot = await document.GetSyntaxRootAsync(cancellationToken).ConfigureAwait(false);
-            var oldSemanticModel = await document.GetSemanticModelAsync(cancellationToken).ConfigureAwait(false);
 
             if (!(syntaxRoot.FindNode(diagnostic.Location.SourceSpan, getInnermostNodeForTie: true) is CastExpressionSyntax node))
             {
@@ -68,9 +67,18 @@ private static SyntaxNode GenerateReplacementNode(CastExpressionSyntax node)
                 (LiteralExpressionSyntax)plusMinusSyntax.Operand.WalkDownParentheses();
             var typeToken = node.Type.GetFirstToken();
             var replacementLiteral = literalExpressionSyntax.WithLiteralSuffix(typeToken.Kind());
+
+            var newLeadingTrivia = SyntaxFactory.TriviaList(node.GetLeadingTrivia().Concat(node.CloseParenToken.TrailingTrivia).Concat(node.Expression.GetLeadingTrivia()))
+                .WithoutLeadingWhitespace()
+                .WithoutTrailingWhitespace();
+
+            if (newLeadingTrivia.Count != 0)
+            {
+                newLeadingTrivia = newLeadingTrivia.Add(SyntaxFactory.Space);
+            }
+
             var replacementNode = node.Expression.ReplaceNode(literalExpressionSyntax, replacementLiteral)
-                .WithLeadingTrivia(node.GetLeadingTrivia().Concat(node.CloseParenToken.TrailingTrivia).Concat(node.Expression.GetLeadingTrivia()))
-                .WithTrailingTrivia(node.Expression.GetTrailingTrivia().Concat(node.GetTrailingTrivia()));
+                .WithLeadingTrivia(newLeadingTrivia);
 
             return replacementNode;
         }

StyleCop.Analyzers/StyleCop.Analyzers.Test/ReadabilityRules/SA1139UnitTests.cs

@@ -266,5 +266,47 @@ public void Method()
 
             await VerifyCSharpDiagnosticAsync(testCode, DiagnosticResult.EmptyDiagnosticResults, CancellationToken.None).ConfigureAwait(false);
         }
+
+        /// <summary>
+        /// Verifies that the codefix will not insert extraneous spaces.
+        /// </summary>
+        /// <returns>A <see cref="Task"/> representing the asynchronous unit test.</returns>
+        [Fact]
+        [WorkItem(2901, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/2901")]
+        public async Task TestCodeFixDoesNotAddExtraneousSpacesAsync()
+        {
+            var testCode = @"
+public class TestClass
+{
+    public void TestMethod()
+    {
+        var x = (long)64 * 1024;
+        var y = (double)64 /* test */ * 1024;
+        var z = (long) /* test */ 64 * 1024;
+    }
+}
+";
+
+            var fixedCode = @"
+public class TestClass
+{
+    public void TestMethod()
+    {
+        var x = 64L * 1024;
+        var y = 64D /* test */ * 1024;
+        var z = /* test */ 64L * 1024;
+    }
+}
+";
+
+            DiagnosticResult[] expectedDiagnosticResult =
+            {
+                Diagnostic().WithLocation(6, 17),
+                Diagnostic().WithLocation(7, 17),
+                Diagnostic().WithLocation(8, 17),
+            };
+
+            await VerifyCSharpFixAsync(testCode, expectedDiagnosticResult, fixedCode, CancellationToken.None).ConfigureAwait(false);
+        }
     }
 }