Fix #1878 (SA1133CodeFixProvider crash with System.InvalidCastException)

Author: NikolayIT

StyleCop.Analyzers/StyleCop.Analyzers.CodeFixes/ReadabilityRules/SA1133CodeFixProvider.cs

@@ -51,8 +51,18 @@ 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 violatingAttribute = (AttributeSyntax)syntaxRoot.FindNode(diagnostic.Location.SourceSpan).Parent;
-            var attributeList = (AttributeListSyntax)violatingAttribute.Parent;
+            var nodeInSourceSpan = syntaxRoot.FindNode(diagnostic.Location.SourceSpan);
+            AttributeListSyntax attributeList;
+            if (nodeInSourceSpan.Parent is AttributeListSyntax)
+            {
+                attributeList = (AttributeListSyntax)nodeInSourceSpan.Parent;
+            }
+            else
+            {
+                var violatingAttribute = (AttributeSyntax)nodeInSourceSpan.Parent;
+                attributeList = (AttributeListSyntax)violatingAttribute.Parent;
+            }
+
             var newAttributeLists = new List<AttributeListSyntax>();
 
             var indentationOptions = IndentationOptions.FromDocument(document);

StyleCop.Analyzers/StyleCop.Analyzers.Test/ReadabilityRules/SA1133UnitTests.cs

@@ -166,11 +166,12 @@ public void TestMethod()
         }
 
         /// <summary>
-        /// Repro test for https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/1878.
+        /// Regression test for issue 1878 (SA1133CodeFixProvider crash), https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/1878
+        /// Fixing exception "Unable to cast object of type 'Microsoft.CodeAnalysis.CSharp.Syntax.AttributeListSyntax' to type 'Microsoft.CodeAnalysis.CSharp.Syntax.AttributeSyntax'."
         /// </summary>
         /// <returns>A <see cref="Task"/> representing the asynchronous unit test.</returns>
         [Fact]
-        public async Task ReproFor1878Async()
+        public async Task TestRegressionIssue1878Async()
         {
             var testCode = @"namespace Stylecop_rc1_bug_repro
 {