Update SA1649 for readonly members

Author: sharwell

StyleCop.Analyzers/StyleCop.Analyzers.Test.CSharp8/DocumentationRules/SA1649CSharp8UnitTests.cs

@@ -3,9 +3,114 @@
 
 namespace StyleCop.Analyzers.Test.CSharp8.DocumentationRules
 {
+    using System.Threading;
+    using System.Threading.Tasks;
+    using Microsoft.CodeAnalysis.Testing;
     using StyleCop.Analyzers.Test.CSharp7.DocumentationRules;
+    using Xunit;
+    using static StyleCop.Analyzers.Test.Verifiers.CustomDiagnosticVerifier<StyleCop.Analyzers.DocumentationRules.SA1649FileNameMustMatchTypeName>;
 
     public partial class SA1649CSharp8UnitTests : SA1649CSharp7UnitTests
     {
+        [Fact]
+        [WorkItem(3001, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3001")]
+        public async Task VerifyReadonlyMembersDoNotAffectCorrectFileNameAsync()
+        {
+            var testCode = @"
+namespace TestNamespace
+{
+    public readonly struct TestType
+    {
+        private readonly int value;
+
+        public TestType(int value)
+        {
+            this.value = value;
+        }
+
+        public readonly int GetValue() => this.value;
+
+        public int Property
+        {
+            readonly get => this.value;
+            set => _ = value;
+        }
+
+        public int this[int index]
+        {
+            readonly get => this.value + index;
+            set => _ = value - index;
+        }
+    }
+}
+";
+
+            await VerifyCSharpDiagnosticAsync(fileName: "TestType.cs", testCode, testSettings: null, DiagnosticResult.EmptyDiagnosticResults, CancellationToken.None).ConfigureAwait(false);
+        }
+
+        [Fact]
+        [WorkItem(3001, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3001")]
+        public async Task VerifyWrongFileNameWithReadonlyMembersAsync()
+        {
+            var testCode = @"
+namespace TestNamespace
+{
+    public readonly struct {|#0:TestType|}
+    {
+        private readonly int value;
+
+        public TestType(int value)
+        {
+            this.value = value;
+        }
+
+        public readonly int GetValue() => this.value;
+
+        public int Property
+        {
+            readonly get => this.value;
+            set => _ = value;
+        }
+
+        public int this[int index]
+        {
+            readonly get => this.value + index;
+            set => _ = value - index;
+        }
+    }
+}
+";
+            var fixedCode = @"
+namespace TestNamespace
+{
+    public readonly struct TestType
+    {
+        private readonly int value;
+
+        public TestType(int value)
+        {
+            this.value = value;
+        }
+
+        public readonly int GetValue() => this.value;
+
+        public int Property
+        {
+            readonly get => this.value;
+            set => _ = value;
+        }
+
+        public int this[int index]
+        {
+            readonly get => this.value + index;
+            set => _ = value - index;
+        }
+    }
+}
+";
+
+            var expectedDiagnostic = Diagnostic().WithLocation(0);
+            await VerifyCSharpFixAsync(oldFileName: "WrongFileName.cs", testCode, StyleCopSettings, expectedDiagnostic, newFileName: "TestType.cs", fixedCode, CancellationToken.None).ConfigureAwait(false);
+        }
     }
 }

documentation/SA1649.md

@@ -43,6 +43,10 @@ public class Class1
 }
 ```
 
+A `readonly` modifier on the type (for example a `readonly struct`) or on members inside the first type (such as C# 8
+readonly struct members) does not change the expected file name. The analyzer continues to use the identifier of the
+first non-partial type, so a type declared as `public readonly struct Point` still belongs in `Point.cs`.
+
 ## How to fix violations
 
 To fix a violation of this rule, rename the file to  match the name of the first type from the file.