[pushed] c++: add fixed test [PR118391]

[Marek Polacek]

Tested x86_64-pc-linux-gnu, applying to trunk.

-- >8 --
Fixed by r15-6740.

        PR c++/118391

gcc/testsuite/ChangeLog:

        * g++.dg/cpp2a/lambda-uneval20.C: New test.
---
 gcc/testsuite/g++.dg/cpp2a/lambda-uneval20.C | 15 +++++++++++++++
 1 file changed, 15 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/lambda-uneval20.C

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 00000000000..fa8b504da9d
--- /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() {}

base-commit: 81bcf412c1c221bc2557666a6ca8381dac1de097
-- 
2.47.1