Extract helper method RenameHelper.IsValidNewMemberName

This helper is a combination of work on #436 and #437, and offers a more
flexible solution for avoiding conflicts during rename operations.

Author: sharwell

StyleCop.Analyzers/StyleCop.Analyzers.CodeFixes/Helpers/RenameHelper.cs

@@ -28,5 +28,43 @@ public static async Task<Solution> RenameSymbolAsync(Document document, SyntaxNo
             // TODO: return annotatedSolution instead of newSolution if newSolution contains any new errors (for any project)
             return newSolution;
         }
+
+        public static bool IsValidNewMemberName(SemanticModel semanticModel, ISymbol symbol, string name)
+        {
+            var members = (symbol as INamedTypeSymbol)?.GetMembers(name);
+            if (members.HasValue && !members.Value.IsDefaultOrEmpty)
+            {
+                return false;
+            }
+
+            var containingSymbol = symbol.ContainingSymbol as INamespaceOrTypeSymbol;
+            if (containingSymbol == null)
+            {
+                return true;
+            }
+
+            if (containingSymbol.Kind == SymbolKind.Namespace)
+            {
+                // Make sure to use the compilation namespace so interfaces in referenced assemblies are considered
+                containingSymbol = semanticModel.Compilation.GetCompilationNamespace((INamespaceSymbol)containingSymbol);
+            }
+            else if (containingSymbol.Kind == SymbolKind.NamedType)
+            {
+                // The name can't be the same as the name of the containing type
+                if (containingSymbol.Name == name)
+                {
+                    return false;
+                }
+            }
+
+            // The name can't be the same as the name of an other member of the same type
+            members = containingSymbol.GetMembers(name);
+            if (!members.Value.IsDefaultOrEmpty)
+            {
+                return false;
+            }
+
+            return true;
+        }
     }
 }

StyleCop.Analyzers/StyleCop.Analyzers.CodeFixes/NamingRules/SA1302CodeFixProvider.cs

@@ -54,25 +54,10 @@ private static async Task<Solution> CreateChangedSolutionAsync(Document document
 
             var semanticModel = await document.GetSemanticModelAsync(cancellationToken).ConfigureAwait(false);
             var declaredSymbol = semanticModel.GetDeclaredSymbol(token.Parent, cancellationToken);
-            INamedTypeSymbol interfaceType = declaredSymbol as INamedTypeSymbol;
-            if (interfaceType != null)
+            while (!RenameHelper.IsValidNewMemberName(semanticModel, declaredSymbol, newName))
             {
-                var containingSymbol = interfaceType.ContainingSymbol as INamespaceOrTypeSymbol;
-                var containingNamespace = containingSymbol as INamespaceSymbol;
-                if (containingNamespace != null)
-                {
-                    // Make sure to use the compilation namespace so interfaces in referenced assemblies are considered
-                    containingSymbol = semanticModel.Compilation.GetCompilationNamespace(containingNamespace);
-                }
-
-                if (containingSymbol != null)
-                {
-                    while (containingSymbol.GetMembers(newName).Any())
-                    {
-                        index++;
-                        newName = baseName + index;
-                    }
-                }
+                index++;
+                newName = baseName + index;
             }
 
             return await RenameHelper.RenameSymbolAsync(document, root, token, newName, cancellationToken).ConfigureAwait(false);