[clang] [clang] Add test for CWG156 "Name lookup for conversion functions" (PR #121654)

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@@ -922,6 +922,49 @@ namespace cwg155 { // cwg155: dup 632
   // expected-warning at -1 {{braces around scalar initializer}}
 }
 
+namespace cwg156 { // cwg156: partial
+namespace ex1 {
+struct A {
+  operator int();
+} a;
+void foo() {
+  typedef int T;
+  a.operator T(); // T is found using unqualified lookup
+                  // after qualified lookup in A fails.
+}
+} // namespace ex1
+
+namespace ex2 {
+struct A {
+  typedef int T;
+  operator T();
+};
+struct B : A {
+  operator T();
+} b;
+void foo() {
+  b.A::operator T(); // FIXME: qualified lookup should find T in A.
+  // expected-error at -1 {{unknown type name 'T'}}
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cor3ntin wrote:

This seems to be #28181
Do we want to take a crack at it?

https://github.com/llvm/llvm-project/pull/121654