Update SA1119 for pattern matching

Author: sharwell

StyleCop.Analyzers/StyleCop.Analyzers.Test.CSharp8/MaintainabilityRules/SA1119CSharp8UnitTests.cs

@@ -328,5 +328,90 @@ public void TestMethod()
 
             await test.RunAsync(CancellationToken.None).ConfigureAwait(false);
         }
+
+        [Fact]
+        [WorkItem(3003, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3003")]
+        public async Task TestReturnSwitchExpressionWithUnnecessaryParenthesisAsync()
+        {
+            const string testCode = @"
+public class TestClass
+{
+    public object TestMethod(int n, object a, object b)
+    {
+        return {|#0:{|#1:(|}n switch { 1 => a, _ => b }{|#2:)|}|};
+    }
+}
+";
+
+            const string fixedCode = @"
+public class TestClass
+{
+    public object TestMethod(int n, object a, object b)
+    {
+        return n switch { 1 => a, _ => b };
+    }
+}
+";
+
+            DiagnosticResult[] expected =
+            {
+                Diagnostic(DiagnosticId).WithLocation(0),
+                Diagnostic(ParenthesesDiagnosticId).WithLocation(1),
+                Diagnostic(ParenthesesDiagnosticId).WithLocation(2),
+            };
+
+            await VerifyCSharpFixAsync(testCode, expected, fixedCode, CancellationToken.None).ConfigureAwait(false);
+        }
+
+        [Fact]
+        [WorkItem(3003, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3003")]
+        public async Task TestPropertyPatternWithUnnecessaryParenthesisAsync()
+        {
+            const string testCode = @"
+public class TestClass
+{
+    public bool TestMethod(string value)
+    {
+        return {|#0:{|#1:(|}value is { Length: 1 }{|#2:)|}|};
+    }
+}
+";
+
+            const string fixedCode = @"
+public class TestClass
+{
+    public bool TestMethod(string value)
+    {
+        return value is { Length: 1 };
+    }
+}
+";
+
+            DiagnosticResult[] expected =
+            {
+                Diagnostic(DiagnosticId).WithLocation(0),
+                Diagnostic(ParenthesesDiagnosticId).WithLocation(1),
+                Diagnostic(ParenthesesDiagnosticId).WithLocation(2),
+            };
+
+            await VerifyCSharpFixAsync(testCode, expected, fixedCode, CancellationToken.None).ConfigureAwait(false);
+        }
+
+        [Fact]
+        [WorkItem(3003, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3003")]
+        public async Task TestNegatedPropertyPatternIsNotReportedAsync()
+        {
+            const string testCode = @"
+public class TestClass
+{
+    public bool TestMethod(string value)
+    {
+        return !(value is { Length: 0 });
+    }
+}
+";
+
+            await VerifyCSharpDiagnosticAsync(testCode, DiagnosticResult.EmptyDiagnosticResults, CancellationToken.None).ConfigureAwait(false);
+        }
     }
 }

documentation/SA1119.md

@@ -44,6 +44,11 @@ string y = this.Method().ToString();
 return x.Value;
 ```
 
+Starting with C# 8.0, parenthesis may be required around switch expressions or pattern-matching expressions when they
+participate in other operations (for example, casts, `await`, conditional/element/member access, or logical negation).
+SA1119 will not report parenthesis that are necessary for correctness, but it will still flag parenthesis that are
+purely redundant, such as `return (value switch { ... });` or `var flag = (input is { Length: 1 });`.
+
 ## How to fix violations
 
 To fix a violation of this rule, remove the unnecessary parenthesis.