Update SA1309/SX1309 for pattern matching

Author: sharwell

StyleCop.Analyzers/StyleCop.Analyzers.Test.CSharp8/NamingRules/SA1309CSharp8UnitTests.cs

@@ -3,9 +3,67 @@
 
 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.SA1309FieldNamesMustNotBeginWithUnderscore,
+        StyleCop.Analyzers.NamingRules.SA1309CodeFixProvider>;
 
     public partial class SA1309CSharp8UnitTests : SA1309CSharp7UnitTests
     {
+        [Fact]
+        [WorkItem(3003, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3003")]
+        public async Task TestDiscardDesignationInPropertyPatternAsync()
+        {
+            var testCode = @"
+public class TestClass
+{
+    public int Test(SomeType value)
+    {
+        if (value is { Number: _ })
+        {
+            return 1;
+        }
+
+        return 0;
+    }
+}
+
+public class SomeType
+{
+    public int Number { get; set; }
+}
+";
+
+            await VerifyCSharpDiagnosticAsync(testCode, DiagnosticResult.EmptyDiagnosticResults, CancellationToken.None).ConfigureAwait(false);
+        }
+
+        [Fact]
+        [WorkItem(3003, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3003")]
+        public async Task TestDiscardDesignationInSwitchExpressionAsync()
+        {
+            var testCode = @"
+public class TestClass
+{
+    public int Test(SomeType value) =>
+        value switch
+        {
+            { Number: _ } => 1,
+            _ => 0,
+        };
+}
+
+public class SomeType
+{
+    public int Number { get; set; }
+}
+";
+
+            await VerifyCSharpDiagnosticAsync(testCode, DiagnosticResult.EmptyDiagnosticResults, CancellationToken.None).ConfigureAwait(false);
+        }
     }
 }

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

@@ -3,9 +3,67 @@
 
 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(3003, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3003")]
+        public async Task TestDiscardDesignationInPropertyPatternAsync()
+        {
+            var testCode = @"
+public class TestClass
+{
+    public int Test(SomeType value)
+    {
+        if (value is { Number: _ })
+        {
+            return 1;
+        }
+
+        return 0;
+    }
+}
+
+public class SomeType
+{
+    public int Number { get; set; }
+}
+";
+
+            await VerifyCSharpDiagnosticAsync(testCode, DiagnosticResult.EmptyDiagnosticResults, CancellationToken.None).ConfigureAwait(false);
+        }
+
+        [Fact]
+        [WorkItem(3003, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3003")]
+        public async Task TestDiscardDesignationInSwitchExpressionAsync()
+        {
+            var testCode = @"
+public class TestClass
+{
+    public int Test(SomeType value) =>
+        value switch
+        {
+            { Number: _ } => 1,
+            _ => 0,
+        };
+}
+
+public class SomeType
+{
+    public int Number { get; set; }
+}
+";
+
+            await VerifyCSharpDiagnosticAsync(testCode, DiagnosticResult.EmptyDiagnosticResults, CancellationToken.None).ConfigureAwait(false);
+        }
     }
 }

documentation/SA1309.md

@@ -27,6 +27,8 @@ By default, StyleCop disallows the use of underscores, *m_*, etc., to mark local
 
 If the field or variable name is intended to match the name of an item associated with Win32 or COM, and thus needs to begin with an underscore, place the field or variable within a special *NativeMethods* class. A NativeMethods class is any class which contains a name ending in NativeMethods, and is intended as a placeholder for Win32 or COM wrappers. StyleCop will ignore this violation if the item is placed within a NativeMethods class.
 
+Discard designations introduced by pattern matching (for example, `_` in C# 8 property or positional patterns) are not subject to this rule.
+
 ## How to fix violations
 
 To fix a violation of this rule, remove the underscore from the beginning of the field name, or place the item within a NativeMethods class if appropriate.

documentation/SX1309.md

@@ -36,6 +36,8 @@ This rule only checks the name of private instance fields.
 
 The fix an instance of this violation, add an underscore (`_`) prefix to the name of the field.
 
+Discard designations introduced by pattern matching (for example, `_` in C# 8 property or positional patterns) are not considered fields and are ignored by this rule.
+
 ## How to suppress violations
 
 ```csharp