Index: clang/lib/Format/TokenAnnotator.cpp
===================================================================
--- clang/lib/Format/TokenAnnotator.cpp
+++ clang/lib/Format/TokenAnnotator.cpp
@@ -2931,6 +2931,14 @@
     // interpolated strings. Interpolated strings are merged into a single token
     // so cannot have spaces inserted by this function.
 
+    // No space between 'this' and '['
+    if (Left.is(tok::kw_this) && Right.is(tok::l_square))
+      return false;
+
+    // No space between 'new' and '('
+    if (Left.is(tok::kw_new) && Right.is(tok::l_paren))
+      return false;
+
     // Space before { (including space within '{ {').
     if (Right.is(tok::l_brace))
       return true;
Index: clang/unittests/Format/FormatTestCSharp.cpp
===================================================================
--- clang/unittests/Format/FormatTestCSharp.cpp
+++ clang/unittests/Format/FormatTestCSharp.cpp
@@ -627,6 +627,8 @@
   verifyFormat(R"(taskContext.Factory.Run(async () => doThing(args);)", Style);
   verifyFormat(R"(catch (TestException) when (innerFinallyExecuted))", Style);
   verifyFormat(R"(private float[,] Values;)", Style);
+  verifyFormat(R"(Result this[Index x] => Foo(x);)", Style);
+  verifyFormat(R"(class ItemFactory<T> where T : new() {})", Style);
 
   Style.SpacesInSquareBrackets = true;
   verifyFormat(R"(private float[ , ] Values;)", Style);