[pushed] c++: Add test for C++20 NB comment CA107.

[Jason Merrill]

We already implemented this, but it's good to have a test.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/concepts-ca107.C: New test.
---
 gcc/testsuite/g++.dg/cpp2a/concepts-ca107.C | 33 +++++++++++++++++++++
 1 file changed, 33 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-ca107.C

diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-ca107.C b/gcc/testsuite/g++.dg/cpp2a/concepts-ca107.C
new file mode 100644
index 00000000000..e18280a04bc
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-ca107.C
@@ -0,0 +1,33 @@
+// NB comments CA107/US117
+// { dg-do compile { target concepts } }
+
+template <unsigned N> constexpr bool Atomic = true;
+template <unsigned N> concept C = Atomic<N>;
+template <unsigned N> concept Add1 = C<N + 1>;
+template <unsigned N> concept AddOne = C<N + 1>;
+template <unsigned M> void f()
+  requires Add1<2 * M>;
+template <unsigned M> int f()
+  requires AddOne<2 * M> && true;
+
+int x = f<0>(); // OK, the atomic constraints from concept C in both fs are Atomic<N>
+		// with mapping similar to N -> 2 * M + 1
+
+template <unsigned N> struct WrapN;
+template <unsigned N> using Add1Ty = WrapN<N + 1>;
+template <unsigned N> using AddOneTy = WrapN<N + 1>;
+template <unsigned M> void g(Add1Ty<2 * M> *);
+template <unsigned M> void g(AddOneTy<2 * M> *);
+
+void h() {
+  g<0>(nullptr); // OK, there is only one g
+}
+template <unsigned N> void f2()
+  requires Add1<2 * N>;
+template <unsigned N> int f2()
+  requires Add1<N * 2> && true;
+void h2() {
+  f2<0>(); // { dg-error "ambiguous" } ill-formed, no diagnostic required:
+	   // required determination of subsumption between atomic constraints that are
+	   // functionally equivalent but not equivalent
+}

base-commit: 14c831f5ef614aabb6a8c85712fb166600e6cc05
-- 
2.18.1