[PATCH] c++: constraints and address of template-id

[Patrick Palka via Gcc-patches]

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.

Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK to
commit?

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.
---
 gcc/cp/pt.c                               |  5 ++++-
 gcc/testsuite/g++.dg/concepts/fn8.C       |  2 +-
 gcc/testsuite/g++.dg/cpp2a/concepts-fn1.C |  2 +-
 gcc/testsuite/g++.dg/cpp2a/concepts-fn5.C | 16 ++++++++++++++++
 gcc/testsuite/g++.dg/cpp2a/concepts-ts2.C |  2 +-
 gcc/testsuite/g++.dg/cpp2a/concepts-ts3.C |  2 +-
 6 files changed, 24 insertions(+), 5 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-fn5.C

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index e7496002c1c..bcfe8d146b1 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -22122,6 +22122,8 @@ resolve_overloaded_unification (tree tparms,
              && !any_dependent_template_arguments_p (subargs))
            {
              fn = instantiate_template (fn, subargs, tf_none);
+             if (!constraints_satisfied_p (fn))
+               continue;
              if (undeduced_auto_decl (fn))
                {
                  /* Instantiate the function to deduce its return type.  */
@@ -22268,7 +22270,8 @@ resolve_nondeduced_context (tree orig_expr, 
tsubst_flags_t complain)
                  badfn = fn;
                  badargs = subargs;
                }
-             else if (elem && (!goodfn || !decls_match (goodfn, elem)))
+             else if (elem && (!goodfn || !decls_match (goodfn, elem))
+                      && constraints_satisfied_p (elem))
                {
                  goodfn = elem;
                  ++good;
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..c01cedde28e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-fn5.C
@@ -0,0 +1,16 @@
+// Verify we check 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" }
 }
 
 
-- 
2.28.0.97.gdc04167d37