c++: add fixed test [PR118391]

Fixed by r15-6740.

	PR c++/118391

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/lambda-uneval20.C: New test.

1 files changed, 15 insertions, 0 deletions

diff --git a/gcc/testsuite/g++.dg/cpp2a/lambda-uneval20.C b/gcc/testsuite/g++.dg/cpp2a/lambda-uneval20.C
new file mode 100644
index 0000000..fa8b504
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/lambda-uneval20.C
@@ -0,0 +1,15 @@
+// PR c++/118391
+// { dg-do compile { target c++20 } }
+
+template<typename>
+using A = int;
+
+template<typename T>
+using B = decltype([]<typename> {}.template operator()<T>());
+
+template<typename T>
+using C = A<B<T>>;
+
+C<int> x;
+
+int main() {}