Update SX1309/SX1309S for readonly members

Author: sharwell

StyleCop.Analyzers/StyleCop.Analyzers.Test.CSharp8/NamingRules/SX1309CSharp8UnitTests.cs

@@ -3,9 +3,62 @@
 
 namespace StyleCop.Analyzers.Test.CSharp8.NamingRules
 {
+    using System.Threading;
+    using System.Threading.Tasks;
+    using Microsoft.CodeAnalysis.Testing;
     using StyleCop.Analyzers.Test.CSharp7.NamingRules;
+    using Xunit;
+    using static StyleCop.Analyzers.Test.Verifiers.StyleCopCodeFixVerifier<
+        StyleCop.Analyzers.NamingRules.SX1309FieldNamesMustBeginWithUnderscore,
+        StyleCop.Analyzers.NamingRules.SX1309CodeFixProvider>;
 
     public partial class SX1309CSharp8UnitTests : SX1309CSharp7UnitTests
     {
+        [Fact]
+        [WorkItem(3001, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3001")]
+        public async Task TestReadonlyMembersDoNotTriggerAsync()
+        {
+            var testCode = @"public struct TestStruct
+{
+    public readonly void Method() { }
+    public int Property { readonly get; set; }
+}";
+
+            await VerifyCSharpDiagnosticAsync(testCode, DiagnosticResult.EmptyDiagnosticResults, CancellationToken.None).ConfigureAwait(false);
+        }
+
+        [Fact]
+        [WorkItem(3001, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3001")]
+        public async Task TestPrivateReadonlyFieldRequiresUnderscoreAsync()
+        {
+            var testCode = @"public struct TestStruct
+{
+    private readonly int {|#0:value|};
+    public readonly void Method() { }
+}";
+
+            var fixedCode = @"public struct TestStruct
+{
+    private readonly int _value;
+    public readonly void Method() { }
+}";
+
+            DiagnosticResult expected = Diagnostic().WithLocation(0).WithArguments("value");
+
+            await VerifyCSharpFixAsync(testCode, expected, fixedCode, CancellationToken.None).ConfigureAwait(false);
+        }
+
+        [Fact]
+        [WorkItem(3001, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3001")]
+        public async Task TestStaticReadonlyFieldIgnoredAsync()
+        {
+            var testCode = @"public struct TestStruct
+{
+    private static readonly int value = 0;
+    public readonly void Method() { }
+}";
+
+            await VerifyCSharpDiagnosticAsync(testCode, DiagnosticResult.EmptyDiagnosticResults, CancellationToken.None).ConfigureAwait(false);
+        }
     }
 }

StyleCop.Analyzers/StyleCop.Analyzers.Test.CSharp8/NamingRules/SX1309SCSharp8UnitTests.cs

@@ -3,9 +3,62 @@
 
 namespace StyleCop.Analyzers.Test.CSharp8.NamingRules
 {
+    using System.Threading;
+    using System.Threading.Tasks;
+    using Microsoft.CodeAnalysis.Testing;
     using StyleCop.Analyzers.Test.CSharp7.NamingRules;
+    using Xunit;
+    using static StyleCop.Analyzers.Test.Verifiers.StyleCopCodeFixVerifier<
+        StyleCop.Analyzers.NamingRules.SX1309SStaticFieldNamesMustBeginWithUnderscore,
+        StyleCop.Analyzers.NamingRules.SX1309CodeFixProvider>;
 
     public partial class SX1309SCSharp8UnitTests : SX1309SCSharp7UnitTests
     {
+        [Fact]
+        [WorkItem(3001, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3001")]
+        public async Task TestReadonlyMembersDoNotTriggerAsync()
+        {
+            var testCode = @"public struct TestStruct
+{
+    public readonly void Method() { }
+    public int Property { readonly get; set; }
+}";
+
+            await VerifyCSharpDiagnosticAsync(testCode, DiagnosticResult.EmptyDiagnosticResults, CancellationToken.None).ConfigureAwait(false);
+        }
+
+        [Fact]
+        [WorkItem(3001, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3001")]
+        public async Task TestPrivateStaticFieldRequiresUnderscoreAsync()
+        {
+            var testCode = @"public struct TestStruct
+{
+    private static int {|#0:value|};
+    public readonly void Method() { }
+}";
+
+            var fixedCode = @"public struct TestStruct
+{
+    private static int _value;
+    public readonly void Method() { }
+}";
+
+            DiagnosticResult expected = Diagnostic().WithLocation(0).WithArguments("value");
+
+            await VerifyCSharpFixAsync(testCode, expected, fixedCode, CancellationToken.None).ConfigureAwait(false);
+        }
+
+        [Fact]
+        [WorkItem(3001, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3001")]
+        public async Task TestStaticReadonlyFieldIgnoredAsync()
+        {
+            var testCode = @"public struct TestStruct
+{
+    private static readonly int value = 0;
+    public readonly void Method() { }
+}";
+
+            await VerifyCSharpDiagnosticAsync(testCode, DiagnosticResult.EmptyDiagnosticResults, CancellationToken.None).ConfigureAwait(false);
+        }
     }
 }

documentation/SX1309.md

@@ -30,7 +30,10 @@ A violation of this rule occurs when a field name does not begin with an undersc
 
 ### Detailed Behavior
 
-This rule only checks the name of private instance fields.
+This rule only checks the name of private instance fields. It ignores fields that are `static`, `const`, or have public,
+internal, or protected accessibility. In C# 8 and later, `readonly` instance members on structs (e.g. `readonly` methods
+or accessors) are not considered by this rule; only private fields—including private `readonly` fields—need the
+underscore prefix. Static `readonly` fields are ignored by this rule (they are treated like constants).
 
 ## How to fix violations
 

documentation/SX1309S.md

@@ -30,7 +30,9 @@ A violation of this rule occurs when a static field name does not begin with an
 
 ### Detailed Behavior
 
-This rule only checks the name of private, static, non-`readonly` fields.
+This rule only checks the name of private, static fields that are neither `const` nor `readonly`. Static `readonly`
+fields are treated like constants and are ignored. C# 8 `readonly` struct members (methods, properties, indexers) are
+not analyzed by this rule.
 
 ## How to fix violations