[clang] [Clang] Handle ?: operator in fold expression (PR #164019)

[Erich Keane via cfe-commits]

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@@ -12,3 +12,8 @@ template <typename... U> struct A {
     foo<T>((... + static_cast<U>(1))); // expected-error {{expression contains unexpanded parameter pack 'T'}}
   }
 };
+
+template <typename ... T>
+void foo(T... Params) {
+  (Params ?: 1, ...); // expected-error {{expression not permitted as operand of fold expression}}
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erichkeane wrote:

Yeah, a note saying what is not permitted is a really good idea.  We can start with just this

https://github.com/llvm/llvm-project/pull/164019