SA1316: allow discards in tuple

Author: Zhang Shen

StyleCop.Analyzers/StyleCop.Analyzers.Test.CSharp7/NamingRules/SA1316CSharp7UnitTests.cs

@@ -346,5 +346,22 @@ public void MethodName(List<(string Name, string Value)> list)
 
             await VerifyCSharpDiagnosticAsync(languageVersion: null, testCode, PascalCaseTestSettings, DiagnosticResult.EmptyDiagnosticResults, CancellationToken.None).ConfigureAwait(false);
         }
+
+        [Fact]
+        [WorkItem(3139, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3139")]
+        public async Task TestTupleDesconstructionDiscardAsync()
+        {
+            var testCode = @"
+public class TypeName
+{
+    public void MethodName((string Name, string Value) obj)
+    {
+        (string name, _) = obj;
+    }
+}
+";
+
+            await VerifyCSharpDiagnosticAsync(LanguageVersionEx.CSharp7, testCode, DefaultTestSettings, DiagnosticResult.EmptyDiagnosticResults, CancellationToken.None).ConfigureAwait(false);
+        }
     }
 }

StyleCop.Analyzers/StyleCop.Analyzers/NamingRules/SA1316TupleElementNamesShouldUseCorrectCasing.cs

@@ -106,6 +106,11 @@ private static void CheckTupleElement(SyntaxNodeAnalysisContext context, StyleCo
 
         private static void CheckName(SyntaxNodeAnalysisContext context, StyleCopSettings settings, string tupleElementName, Location location, bool prepareCodeFix)
         {
+            if (tupleElementName == "_")
+            {
+                return;
+            }
+
             var firstCharacterIsLower = char.IsLower(tupleElementName[0]);
 
             bool reportDiagnostic;