Fix behavior of SA1506 when a blank line follows a line comment

Fixes #1456

Author: sharwell

StyleCop.Analyzers/StyleCop.Analyzers.Test/LayoutRules/SA1506UnitTests.cs

@@ -572,9 +572,14 @@ public class TestClass
     public void TestMethod1() { }
 
     /// <summary>more documentation.</summary>
-    
+
     /* another comment */
     public void TestMethod2() { }
+
+    /// <summary>more documentation.</summary>
+    // another comment (a specific regression test for https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/1456)
+
+    public void TestMethod3() { }
 }
 ";
 
@@ -592,6 +597,10 @@ public void TestMethod1() { }
     /// <summary>more documentation.</summary>
     /* another comment */
     public void TestMethod2() { }
+
+    /// <summary>more documentation.</summary>
+    // another comment (a specific regression test for https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/1456)
+    public void TestMethod3() { }
 }
 ";
 
@@ -600,6 +609,7 @@ public void TestMethod2() { }
                 this.CSharpDiagnostic().WithLocation(3, 1),
                 this.CSharpDiagnostic().WithLocation(10, 1),
                 this.CSharpDiagnostic().WithLocation(15, 1),
+                this.CSharpDiagnostic().WithLocation(20, 1),
             };
 
             await this.VerifyCSharpDiagnosticAsync(testCode, expected, CancellationToken.None).ConfigureAwait(false);

StyleCop.Analyzers/StyleCop.Analyzers/LayoutRules/SA1506CodeFixProvider.cs

@@ -52,32 +52,50 @@ private static async Task<Document> GetTransformedDocumentAsync(Document documen
             var triviaList = token.LeadingTrivia;
 
             var index = triviaList.IndexOf(SyntaxKind.SingleLineDocumentationCommentTrivia);
-            for (; index < triviaList.Count - 1; index++)
+
+            int currentLineStart = index + 1;
+            bool onBlankLine = true;
+            for (int currentIndex = currentLineStart; currentIndex < triviaList.Count; currentIndex++)
             {
-                if (triviaList[index].IsKind(SyntaxKind.SingleLineCommentTrivia)
-                    || triviaList[index].IsKind(SyntaxKind.MultiLineCommentTrivia))
+                switch (triviaList[currentIndex].Kind())
                 {
-                    break;
-                }
-            }
+                case SyntaxKind.EndOfLineTrivia:
+                    if (onBlankLine)
+                    {
+                        for (int i = 0; i < currentIndex - currentLineStart + 1; i++)
+                        {
+                            triviaList = triviaList.RemoveAt(currentLineStart);
+                            currentIndex = currentLineStart - 1;
+                        }
 
-            while (!triviaList[index].IsKind(SyntaxKind.EndOfLineTrivia))
-            {
-                index--;
-            }
+                        continue;
+                    }
+                    else
+                    {
+                        currentLineStart = currentIndex + 1;
+                        onBlankLine = true;
+                        break;
+                    }
 
-            var lastEndOfLine = index;
+                case SyntaxKind.WhitespaceTrivia:
+                    break;
 
-            while (!triviaList[index].IsKind(SyntaxKind.SingleLineDocumentationCommentTrivia))
-            {
-                index--;
+                default:
+                    if (triviaList[currentIndex].HasBuiltinEndLine())
+                    {
+                        currentLineStart = currentIndex + 1;
+                        onBlankLine = true;
+                        break;
+                    }
+                    else
+                    {
+                        onBlankLine = false;
+                        break;
+                    }
+                }
             }
 
-            var lastDocumentation = index;
-
-            var newLeadingTrivia = triviaList.Take(lastDocumentation + 1).Concat(triviaList.Skip(lastEndOfLine + 1));
-            var newSyntaxRoot = syntaxRoot.ReplaceToken(token, token.WithLeadingTrivia(newLeadingTrivia));
-
+            var newSyntaxRoot = syntaxRoot.ReplaceToken(token, token.WithLeadingTrivia(triviaList));
             return document.WithSyntaxRoot(newSyntaxRoot);
         }
     }