Spacing between this and open-paren in tuple extension method (#15967)

src/Workspaces/CSharp/Portable/Formatting/Rules/TokenBasedFormattingRule.cs

@@ -193,6 +193,14 @@ public override AdjustSpacesOperation GetAdjustSpacesOperation(SyntaxToken previ
                 return CreateAdjustSpacesOperation(0, AdjustSpacesOption.ForceSpacesIfOnSingleLine);
             }
 
+            // extension method on tuple type
+            // M(this (
+            if (currentToken.Kind() == SyntaxKind.OpenParenToken &&
+                previousToken.Kind() == SyntaxKind.ThisKeyword)
+            {
+                return CreateAdjustSpacesOperation(1, AdjustSpacesOption.ForceSpacesIfOnSingleLine);
+            }
+
             // some * "(" cases
             if (currentToken.Kind() == SyntaxKind.OpenParenToken)
             {

src/Workspaces/CSharpTest/Formatting/FormattingTests.cs

@@ -4463,6 +4463,22 @@ void bar()
             await AssertFormatAsync(expectedCode, code);
         }
 
+        [Fact]
+        [Trait(Traits.Feature, Traits.Features.Formatting)]
+        public async Task SpacingInTupleExtension()
+        {
+            var code = @"static class Class5
+{
+    static void Extension(this(int, string) self) { }
+}";
+            var expectedCode = @"static class Class5
+{
+    static void Extension(this (int, string) self) { }
+}";
+
+            await AssertFormatAsync(expectedCode, code);
+        }
+
         [Fact]
         [Trait(Traits.Feature, Traits.Features.Formatting)]
         public async Task SpacingInNestedDeconstruction()