Update SA1135 to support file-scoped namespaces

Fixes #3415

Author: sharwell

StyleCop.Analyzers/StyleCop.Analyzers.Test.CSharp10/ReadabilityRules/SA1135CSharp10UnitTests.cs

@@ -3,9 +3,53 @@
 
 namespace StyleCop.Analyzers.Test.CSharp10.ReadabilityRules
 {
+    using System.Threading;
+    using System.Threading.Tasks;
+    using Microsoft.CodeAnalysis.Testing;
     using StyleCop.Analyzers.Test.CSharp9.ReadabilityRules;
+    using Xunit;
+    using static StyleCop.Analyzers.Test.Verifiers.StyleCopCodeFixVerifier<
+        StyleCop.Analyzers.ReadabilityRules.SA1135UsingDirectivesMustBeQualified,
+        StyleCop.Analyzers.ReadabilityRules.SA1135CodeFixProvider>;
 
     public class SA1135CSharp10UnitTests : SA1135CSharp9UnitTests
     {
+        [Fact]
+        [WorkItem(3415, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3415")]
+        public async Task TestFileScopedNamespaceAsync()
+        {
+            var testCode = @"
+namespace TestNamespace
+{
+    using KeyValue = System.Collections.Generic.KeyValuePair<string, object?>;
+}
+";
+            await VerifyCSharpDiagnosticAsync(testCode, DiagnosticResult.EmptyDiagnosticResults, CancellationToken.None).ConfigureAwait(false);
+            await new CSharpTest
+            {
+                TestState =
+                {
+                    Sources =
+                    {
+                        @"namespace A.B.C { }",
+                        @"namespace A.B.D;
+
+[|using C;|]
+",
+                    },
+                },
+                FixedState =
+                {
+                    Sources =
+                    {
+                        @"namespace A.B.C { }",
+                        @"namespace A.B.D;
+
+using A.B.C;
+",
+                    },
+                },
+            }.RunAsync(CancellationToken.None).ConfigureAwait(false);
+        }
     }
 }

StyleCop.Analyzers/StyleCop.Analyzers/ReadabilityRules/SA1135UsingDirectivesMustBeQualified.cs

@@ -67,7 +67,8 @@ private static void HandleUsingDeclaration(SyntaxNodeAnalysisContext context)
 
         private static void CheckUsingDeclaration(SyntaxNodeAnalysisContext context, UsingDirectiveSyntax usingDirective)
         {
-            if (!usingDirective.Parent.IsKind(SyntaxKind.NamespaceDeclaration))
+            if (!usingDirective.Parent.IsKind(SyntaxKind.NamespaceDeclaration)
+                && !usingDirective.Parent.IsKind(SyntaxKindEx.FileScopedNamespaceDeclaration))
             {
                 // Usings outside of a namespace are always qualified.
                 return;
@@ -104,7 +105,7 @@ private static void CheckUsingDeclaration(SyntaxNodeAnalysisContext context, Usi
                     break;
 
                 case SymbolKind.NamedType:
-                    var containingNamespace = ((NamespaceDeclarationSyntax)usingDirective.Parent).Name.ToString();
+                    var containingNamespace = ((BaseNamespaceDeclarationSyntaxWrapper)usingDirective.Parent).Name.ToString();
                     if (containingNamespace != symbol.ContainingNamespace.ToString())
                     {
                         context.ReportDiagnostic(Diagnostic.Create(DescriptorType, usingDirective.GetLocation(), symbolString));