[clang] [Clang] Substitute for the type aliases inside of a CTAD guide (PR #94740)

[Haojian Wu via cfe-commits]

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@@ -16,3 +16,73 @@ using T = A<void>::B<int>;
 
 using Copy = decltype(copy);
 using Copy = A<void>::B<int>;
+
+namespace GH94614 {
+
+template <class, class> struct S {};
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hokein wrote:

I wonder whether it is feasible to add an ast-dump test for this issue, I find seeing and verifying the shape of AST deduction guide is clearer. However, the ast-dump doesn't seem to dump much information about the type of the function parameter decl, which is the information we want to verify. 

https://github.com/llvm/llvm-project/pull/94740