Check for trailing commas in multiline switch expressions

Fixes #3056

Author: sharwell

StyleCop.Analyzers/StyleCop.Analyzers.Test.CSharp8/MaintainabilityRules/SA1413CSharp8UnitTests.cs

@@ -3,9 +3,59 @@
 
 namespace StyleCop.Analyzers.Test.CSharp8.MaintainabilityRules
 {
+    using System.Threading;
+    using System.Threading.Tasks;
+    using Microsoft.CodeAnalysis.CSharp;
+    using Microsoft.CodeAnalysis.Testing;
     using StyleCop.Analyzers.Test.CSharp7.MaintainabilityRules;
+    using Xunit;
+    using static StyleCop.Analyzers.Test.Verifiers.StyleCopCodeFixVerifier<
+        StyleCop.Analyzers.MaintainabilityRules.SA1413UseTrailingCommasInMultiLineInitializers,
+        StyleCop.Analyzers.MaintainabilityRules.SA1413CodeFixProvider>;
 
     public class SA1413CSharp8UnitTests : SA1413CSharp7UnitTests
     {
+        [Fact]
+        [WorkItem(3056, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3056")]
+        public async Task TestSwitchExpressionAsync()
+        {
+            var testCode = @"namespace TestNamespace
+{
+    public class TestClass
+    {
+        public void TestMethod(int input)
+        {
+            int data1 = input switch { 0 => 1, 1 => 2 };
+            int data2 = input switch { 0 => 1, 1 => 2, };
+            int data3 = input switch
+            {
+                0 => 1,
+                [|1 => 2|]
+            };
+        }
+    }
+}
+";
+
+            var fixedCode = @"namespace TestNamespace
+{
+    public class TestClass
+    {
+        public void TestMethod(int input)
+        {
+            int data1 = input switch { 0 => 1, 1 => 2 };
+            int data2 = input switch { 0 => 1, 1 => 2, };
+            int data3 = input switch
+            {
+                0 => 1,
+                1 => 2,
+            };
+        }
+    }
+}
+";
+
+            await VerifyCSharpFixAsync(LanguageVersion.CSharp8, testCode, DiagnosticResult.EmptyDiagnosticResults, fixedCode, CancellationToken.None).ConfigureAwait(false);
+        }
     }
 }

StyleCop.Analyzers/StyleCop.Analyzers/MaintainabilityRules/SA1413UseTrailingCommasInMultiLineInitializers.cs

@@ -11,6 +11,7 @@ namespace StyleCop.Analyzers.MaintainabilityRules
     using Microsoft.CodeAnalysis.CSharp.Syntax;
     using Microsoft.CodeAnalysis.Diagnostics;
     using StyleCop.Analyzers.Helpers;
+    using StyleCop.Analyzers.Lightup;
 
     /// <summary>
     /// A multi-line initializer should use a comma on the last item.
@@ -59,6 +60,7 @@ internal class SA1413UseTrailingCommasInMultiLineInitializers : DiagnosticAnalyz
         private static readonly Action<SyntaxNodeAnalysisContext> HandleObjectInitializerAction = HandleObjectInitializer;
         private static readonly Action<SyntaxNodeAnalysisContext> HandleAnonymousObjectInitializerAction = HandleAnonymousObjectInitializer;
         private static readonly Action<SyntaxNodeAnalysisContext> HandleEnumDeclarationAction = HandleEnumDeclaration;
+        private static readonly Action<SyntaxNodeAnalysisContext> HandleSwitchExpressionAction = HandleSwitchExpression;
 
         private static readonly ImmutableArray<SyntaxKind> ObjectInitializerKinds =
             ImmutableArray.Create(SyntaxKind.ObjectInitializerExpression, SyntaxKind.ArrayInitializerExpression, SyntaxKind.CollectionInitializerExpression);
@@ -76,6 +78,7 @@ public override void Initialize(AnalysisContext context)
             context.RegisterSyntaxNodeAction(HandleObjectInitializerAction, ObjectInitializerKinds);
             context.RegisterSyntaxNodeAction(HandleAnonymousObjectInitializerAction, SyntaxKind.AnonymousObjectCreationExpression);
             context.RegisterSyntaxNodeAction(HandleEnumDeclarationAction, SyntaxKind.EnumDeclaration);
+            context.RegisterSyntaxNodeAction(HandleSwitchExpressionAction, SyntaxKindEx.SwitchExpression);
         }
 
         private static void HandleEnumDeclaration(SyntaxNodeAnalysisContext context)
@@ -120,5 +123,19 @@ private static void HandleAnonymousObjectInitializer(SyntaxNodeAnalysisContext c
                 context.ReportDiagnostic(Diagnostic.Create(Descriptor, initializer.Initializers.Last().GetLocation()));
             }
         }
+
+        private static void HandleSwitchExpression(SyntaxNodeAnalysisContext context)
+        {
+            var switchExpression = (SwitchExpressionSyntaxWrapper)context.Node;
+            if (switchExpression.SyntaxNode == null || !switchExpression.SyntaxNode.SpansMultipleLines())
+            {
+                return;
+            }
+
+            if (switchExpression.Arms.SeparatorCount < switchExpression.Arms.Count)
+            {
+                context.ReportDiagnostic(Diagnostic.Create(Descriptor, switchExpression.Arms.Last().SyntaxNode.GetLocation()));
+            }
+        }
     }
 }