c++: constraints and address of template-id

When resolving the address of a template-id, we need to drop functions
whose associated constraints are not satisfied, as per [over.over].  We
do so in resolve_address_of_overloaded_function, but not in
resolve_overloaded_unification or resolve_nondeduced_context, which
seems like an oversight.

gcc/cp/ChangeLog:

	* pt.c (resolve_overloaded_unification): Drop functions with
	unsatisfied constraints.
	(resolve_nondeduced_context): Likewise.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/concepts-fn5.C: New test.
	* g++.dg/concepts/fn8.C: Generalize dg-error directive to accept
	"no matching function ..." diagnostic.
	* g++.dg/cpp2a/concepts-fn1.C: Likewise.
	* g++.dg/cpp2a/concepts-ts2.C: Likewise.
	* g++.dg/cpp2a/concepts-ts3.C: Likewise.

5 files changed, 21 insertions, 4 deletions

diff --git a/gcc/testsuite/g++.dg/concepts/fn8.C b/gcc/testsuite/g++.dg/concepts/fn8.C
index ed900809908..32df5a556c0 100644
--- a/gcc/testsuite/g++.dg/concepts/fn8.C
+++ b/gcc/testsuite/g++.dg/concepts/fn8.C
@@ -24,5 +24,5 @@ template<typename T>
   void g(T x) { }
 
 int main () {
-  g(&f<int>); // { dg-error "no matches" }
+  g(&f<int>); // { dg-error "no match" }
 }
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-fn1.C b/gcc/testsuite/g++.dg/cpp2a/concepts-fn1.C
index 238eb819e90..b31675d255c 100644
--- a/gcc/testsuite/g++.dg/cpp2a/concepts-fn1.C
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-fn1.C
@@ -170,7 +170,7 @@ template<typename T> void g(T x) { }
 void driver_3 () 
 {
   g(&ok<int>);
-  g(&err<int>); // { dg-error "no matches" }
+  g(&err<int>); // { dg-error "no match" }
 }
 
 
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-fn5.C b/gcc/testsuite/g++.dg/cpp2a/concepts-fn5.C
new file mode 100644
index 00000000000..8f00a760d7e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-fn5.C
@@ -0,0 +1,17 @@
+// Verify we check associated constraints when resolving the address of a
+// template-id.
+// { dg-do compile { target c++20 } }
+
+void id(auto) { }
+
+template <typename>
+int f() { return 0; }
+
+template <typename T> requires requires { T::fail(); }
+auto f() { T::fail(); }
+
+int main() {
+  using U = decltype(&f<int>);
+  (void)&f<int>;
+  id(&f<int>);
+}
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-ts2.C b/gcc/testsuite/g++.dg/cpp2a/concepts-ts2.C
index d28002c035a..5942ff19327 100644
--- a/gcc/testsuite/g++.dg/cpp2a/concepts-ts2.C
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-ts2.C
@@ -173,7 +173,7 @@ template<typename T> void g(T x) { }
 void driver_3 () 
 {
   g(&ok<int>);
-  g(&err<int>); // { dg-error "no matches" }
+  g(&err<int>); // { dg-error "no match" }
 }
 
 
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-ts3.C b/gcc/testsuite/g++.dg/cpp2a/concepts-ts3.C
index 9d47a7a083d..6f7ed1ffee4 100644
--- a/gcc/testsuite/g++.dg/cpp2a/concepts-ts3.C
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-ts3.C
@@ -173,7 +173,7 @@ template<typename T> void g(T x) { }
 void driver_3 () 
 {
   g(&ok<int>);
-  g(&err<int>); // { dg-error "no matches" }
+  g(&err<int>); // { dg-error "no match" }
 }