Updating SA1402 to favor a class with the same name as the file.

If the file does not contain a class of the same name continue to fall
back to the first class in the file.

Author: dcooke28

StyleCop.Analyzers/StyleCop.Analyzers.Test/MaintainabilityRules/SA1402UnitTests.cs

@@ -60,6 +60,27 @@ public partial class Bar
             await this.VerifyCSharpFixAsync(testCode, fixedCode, cancellationToken: CancellationToken.None).ConfigureAwait(false);
         }
 
+        [Fact]
+        public async Task TestPreferFilenameClassAsync()
+        {
+            var testCode = @"public class Foo
+{
+}
+public class Test0
+{
+}";
+
+            var fixedCode = @"public class Test0
+{
+}";
+
+            DiagnosticResult expected = this.CSharpDiagnostic().WithLocation(1, 14);
+
+            await this.VerifyCSharpDiagnosticAsync(testCode, expected, CancellationToken.None).ConfigureAwait(false);
+            await this.VerifyCSharpDiagnosticAsync(fixedCode, EmptyDiagnosticResults, CancellationToken.None).ConfigureAwait(false);
+            await this.VerifyCSharpFixAsync(testCode, fixedCode, cancellationToken: CancellationToken.None).ConfigureAwait(false);
+        }
+
         [Fact]
         public async Task TestNestedClassesAsync()
         {

StyleCop.Analyzers/StyleCop.Analyzers/MaintainabilityRules/SA1402FileMayOnlyContainASingleClass.cs

@@ -5,6 +5,8 @@ namespace StyleCop.Analyzers.MaintainabilityRules
 {
     using System;
     using System.Collections.Immutable;
+    using System.IO;
+    using System.Linq;
     using Microsoft.CodeAnalysis;
     using Microsoft.CodeAnalysis.CSharp;
     using Microsoft.CodeAnalysis.CSharp.Syntax;
@@ -60,37 +62,35 @@ private static void HandleCompilationStart(CompilationStartAnalysisContext conte
         private static void HandleSyntaxTree(SyntaxTreeAnalysisContext context)
         {
             var syntaxRoot = context.Tree.GetRoot(context.CancellationToken);
-
             var descentNodes = syntaxRoot.DescendantNodes(descendIntoChildren: node => node != null && !node.IsKind(SyntaxKind.ClassDeclaration));
+            var classNodes = from descentNode in descentNodes
+                             where descentNode.IsKind(SyntaxKind.ClassDeclaration)
+                             select descentNode as ClassDeclarationSyntax;
 
-            string foundClassName = null;
-            bool isPartialClass = false;
+            var preferredClassNode = classNodes.FirstOrDefault(n => n.Identifier.Text == Path.GetFileNameWithoutExtension(context.Tree.FilePath)) ?? classNodes.FirstOrDefault();
 
-            foreach (var node in descentNodes)
+            if (preferredClassNode != null)
             {
-                if (node.IsKind(SyntaxKind.ClassDeclaration))
+                string foundClassName = null;
+                bool isPartialClass = false;
+
+                foundClassName = preferredClassNode.Identifier.Text;
+                isPartialClass = preferredClassNode.Modifiers.Any(SyntaxKind.PartialKeyword);
+
+                foreach (var classNode in classNodes)
                 {
-                    ClassDeclarationSyntax classDeclaration = node as ClassDeclarationSyntax;
-                    if (foundClassName != null)
+                    if (classNode == preferredClassNode || (isPartialClass && foundClassName == classNode.Identifier.Text))
                     {
-                        if (isPartialClass && foundClassName == classDeclaration.Identifier.Text)
-                        {
-                            continue;
-                        }
-
-                        var location = NamedTypeHelpers.GetNameOrIdentifierLocation(node);
-                        if (location != null)
-                        {
-                            context.ReportDiagnostic(Diagnostic.Create(Descriptor, location));
-                        }
+                        continue;
                     }
-                    else
+
+                    var location = NamedTypeHelpers.GetNameOrIdentifierLocation(classNode);
+                    if (location != null)
                     {
-                        foundClassName = classDeclaration.Identifier.Text;
-                        isPartialClass = classDeclaration.Modifiers.Any(SyntaxKind.PartialKeyword);
+                        context.ReportDiagnostic(Diagnostic.Create(Descriptor, location));
                     }
                 }
             }
         }
     }
-}
+}