Fix SA1008 for positional pattern after comma

Fixes #3198

Author: sharwell

StyleCop.Analyzers/StyleCop.Analyzers.Test.CSharp8/SpacingRules/SA1008CSharp8UnitTests.cs

@@ -109,5 +109,43 @@ await VerifyCSharpFixAsync(
                 fixedCode,
                 CancellationToken.None).ConfigureAwait(false);
         }
+
+        [Fact]
+        [WorkItem(3198, "https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3198")]
+        public async Task TestInPositionalPatternAsync()
+        {
+            var testCode = @"
+class C
+{
+    void M((bool A, bool B) tuple)
+    {
+        _ = (tuple, tuple) is{|#0:(|} (true, true),{|#1:(|} true, true));
+    }
+}
+";
+            var fixedCode = @"
+class C
+{
+    void M((bool A, bool B) tuple)
+    {
+        _ = (tuple, tuple) is ((true, true), (true, true));
+    }
+}
+";
+            DiagnosticResult[] expectedResults =
+            {
+                Diagnostic(DescriptorPreceded).WithLocation(0),
+                Diagnostic(DescriptorNotFollowed).WithLocation(0),
+                Diagnostic(DescriptorPreceded).WithLocation(1),
+                Diagnostic(DescriptorNotFollowed).WithLocation(1),
+            };
+
+            await VerifyCSharpFixAsync(
+                LanguageVersion.CSharp8,
+                testCode,
+                expectedResults,
+                fixedCode,
+                CancellationToken.None).ConfigureAwait(false);
+        }
     }
 }

StyleCop.Analyzers/StyleCop.Analyzers/SpacingRules/SA1008OpeningParenthesisMustBeSpacedCorrectly.cs

@@ -185,7 +185,8 @@ private static void HandleOpenParenToken(SyntaxTreeAnalysisContext context, Synt
                 break;
 
             case SyntaxKindEx.PositionalPatternClause:
-                haveLeadingSpace = prevToken.IsKind(SyntaxKind.IsKeyword);
+                haveLeadingSpace = prevToken.IsKind(SyntaxKind.IsKeyword)
+                    || prevToken.IsKind(SyntaxKind.CommaToken);
                 break;
 
             case SyntaxKind.ArgumentList: