Update SA1209 to support file-scoped namespaces

Fixes #3439

Author: sharwell

StyleCop.Analyzers/StyleCop.Analyzers.Test.CSharp10/OrderingRules/SA1209CSharp10UnitTests.cs

@@ -3,9 +3,46 @@
 
 namespace StyleCop.Analyzers.Test.CSharp10.OrderingRules
 {
+    using System.Threading;
+    using System.Threading.Tasks;
+    using Microsoft.CodeAnalysis.Testing;
     using StyleCop.Analyzers.Test.CSharp9.OrderingRules;
+    using Xunit;
+    using static StyleCop.Analyzers.Test.Verifiers.StyleCopCodeFixVerifier<
+        StyleCop.Analyzers.OrderingRules.SA1209UsingAliasDirectivesMustBePlacedAfterOtherUsingDirectives,
+        StyleCop.Analyzers.OrderingRules.UsingCodeFixProvider>;
 
     public class SA1209CSharp10UnitTests : SA1209CSharp9UnitTests
     {
+        [Fact]
+        [WorkItem(3439, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3439")]
+        public async Task TestWhenUsingAliasDirectivesAreNotPlacedCorrectlyInFileScopedNamespaceAsync()
+        {
+            var testCodeNamespace = @"namespace Test;
+
+using System.Net;
+using System.Threading;
+[|using L = System.Linq;|]
+using System.IO;
+using P = System.Threading.Tasks;
+
+class A
+{
+}
+";
+            var fixedTestCodeNamespace = @"namespace Test;
+using System.IO;
+using System.Net;
+using System.Threading;
+using L = System.Linq;
+using P = System.Threading.Tasks;
+
+class A
+{
+}
+";
+
+            await VerifyCSharpFixAsync(testCodeNamespace, DiagnosticResult.EmptyDiagnosticResults, fixedTestCodeNamespace, CancellationToken.None).ConfigureAwait(false);
+        }
     }
 }

StyleCop.Analyzers/StyleCop.Analyzers/OrderingRules/SA1209UsingAliasDirectivesMustBePlacedAfterOtherUsingDirectives.cs

@@ -10,6 +10,7 @@ namespace StyleCop.Analyzers.OrderingRules
     using Microsoft.CodeAnalysis.CSharp.Syntax;
     using Microsoft.CodeAnalysis.Diagnostics;
     using StyleCop.Analyzers.Helpers;
+    using StyleCop.Analyzers.Lightup;
 
     /// <summary>
     /// A using-alias directive is positioned before a regular using directive.
@@ -37,7 +38,7 @@ internal class SA1209UsingAliasDirectivesMustBePlacedAfterOtherUsingDirectives :
             new DiagnosticDescriptor(DiagnosticId, Title, MessageFormat, AnalyzerCategory.OrderingRules, DiagnosticSeverity.Warning, AnalyzerConstants.EnabledByDefault, Description, HelpLink);
 
         private static readonly Action<SyntaxNodeAnalysisContext> CompilationUnitAction = HandleCompilationUnit;
-        private static readonly Action<SyntaxNodeAnalysisContext> NamespaceDeclarationAction = HandleNamespaceDeclaration;
+        private static readonly Action<SyntaxNodeAnalysisContext> BaseNamespaceDeclarationAction = HandleBaseNamespaceDeclaration;
 
         /// <inheritdoc/>
         public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics { get; } =
@@ -50,7 +51,7 @@ public override void Initialize(AnalysisContext context)
             context.EnableConcurrentExecution();
 
             context.RegisterSyntaxNodeAction(CompilationUnitAction, SyntaxKind.CompilationUnit);
-            context.RegisterSyntaxNodeAction(NamespaceDeclarationAction, SyntaxKind.NamespaceDeclaration);
+            context.RegisterSyntaxNodeAction(BaseNamespaceDeclarationAction, SyntaxKinds.BaseNamespaceDeclaration);
         }
 
         private static void HandleCompilationUnit(SyntaxNodeAnalysisContext context)
@@ -60,9 +61,9 @@ private static void HandleCompilationUnit(SyntaxNodeAnalysisContext context)
             ProcessUsingsAndReportDiagnostic(compilationUnit.Usings, context);
         }
 
-        private static void HandleNamespaceDeclaration(SyntaxNodeAnalysisContext context)
+        private static void HandleBaseNamespaceDeclaration(SyntaxNodeAnalysisContext context)
         {
-            var namespaceDeclaration = (NamespaceDeclarationSyntax)context.Node;
+            var namespaceDeclaration = (BaseNamespaceDeclarationSyntaxWrapper)context.Node;
 
             ProcessUsingsAndReportDiagnostic(namespaceDeclaration.Usings, context);
         }