Added new test case for SA1205 to verify that nested partial types without access modifiers are changed to 'private' by the code fix. Updated code fix accordingly.

Author: bjornhellander

StyleCop.Analyzers/StyleCop.Analyzers.CodeFixes/OrderingRules/SA1205CodeFixProvider.cs

@@ -3,6 +3,7 @@
 
 namespace StyleCop.Analyzers.OrderingRules
 {
+    using System;
     using System.Collections.Immutable;
     using System.Composition;
     using System.Threading;
@@ -59,7 +60,7 @@ private static async Task<Document> GetTransformedDocumentAsync(Document documen
             }
 
             var symbol = semanticModel.GetDeclaredSymbol(typeDeclarationNode);
-            var accessModifierKind = (symbol.DeclaredAccessibility == Accessibility.Public) ? SyntaxKind.PublicKeyword : SyntaxKind.InternalKeyword;
+            var accessModifierKind = GetMissingAccessModifier(symbol.DeclaredAccessibility);
 
             var keywordToken = typeDeclarationNode.Keyword;
 
@@ -70,6 +71,21 @@ private static async Task<Document> GetTransformedDocumentAsync(Document documen
             return document.WithSyntaxRoot(newSyntaxRoot);
         }
 
+        private static SyntaxKind GetMissingAccessModifier(Accessibility accessibility)
+        {
+            switch (accessibility)
+            {
+                case Accessibility.Public:
+                    return SyntaxKind.PublicKeyword;
+                case Accessibility.Internal:
+                    return SyntaxKind.InternalKeyword;
+                case Accessibility.Private:
+                    return SyntaxKind.PrivateKeyword;
+                default:
+                    throw new InvalidOperationException("Unexpected accessibility " + accessibility);
+            }
+        }
+
         // This code was copied from the Roslyn code base (and slightly modified). It can be removed if
         // TypeDeclarationSyntaxExtensions.WithModifiers is made public (Roslyn issue #2186)
         private static TypeDeclarationSyntax ReplaceModifiers(TypeDeclarationSyntax node, SyntaxTokenList modifiers)

StyleCop.Analyzers/StyleCop.Analyzers.Test/OrderingRules/SA1205UnitTests.cs

@@ -200,6 +200,38 @@ internal static partial class TestPartial
             await this.VerifyCSharpDiagnosticAsync(testCode, EmptyDiagnosticResults, CancellationToken.None).ConfigureAwait(false);
         }
 
+        /// <summary>
+        /// Verifies that a nested type without access modifiers will produce a diagnostic and can be fixed correctly.
+        /// </summary>
+        /// <param name="declaration">The declaration to verify.</param>
+        /// <returns>A <see cref="Task"/> representing the asynchronous unit test.</returns>
+        [Theory]
+        [MemberData(nameof(InvalidDeclarations))]
+        public async Task TestNestedTypeWithoutAccessModifierAsync(string declaration)
+        {
+            var testCode = $@"
+public class Foo
+{{
+    {declaration} Bar
+    {{
+    }}
+}}
+";
+
+            var fixedTestCode = $@"
+public class Foo
+{{
+    private {declaration} Bar
+    {{
+    }}
+}}
+";
+
+            await this.VerifyCSharpDiagnosticAsync(testCode, this.CSharpDiagnostic().WithLocation(4, 6 + declaration.Length), CancellationToken.None).ConfigureAwait(false);
+            await this.VerifyCSharpDiagnosticAsync(fixedTestCode, EmptyDiagnosticResults, CancellationToken.None).ConfigureAwait(false);
+            await this.VerifyCSharpFixAsync(testCode, fixedTestCode).ConfigureAwait(false);
+        }
+
         /// <inheritdoc/>
         protected override IEnumerable<DiagnosticAnalyzer> GetCSharpDiagnosticAnalyzers()
         {