[pushed GCC9] c++: Fix SFINAE for invalid non-type tparm types.

[Jason Merrill]

Just missing the usual SFINAE pattern here.  This was fixed for GCC 10 as a
drive-by in r277902.

gcc/cp/ChangeLog
2020-03-05  Jason Merrill  <ja...@redhat.com>

        PR c++/90338
        * pt.c (invalid_nontype_parm_type_p): Check complain for non-literal
        and mutable errors.
---
 gcc/cp/pt.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 43d9660ebda..4787747b6ff 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -25341,15 +25341,20 @@ invalid_nontype_parm_type_p (tree type, 
tsubst_flags_t complain)
        return true;
       if (!literal_type_p (type))
        {
-         error ("%qT is not a valid type for a template non-type parameter "
-                "because it is not literal", type);
-         explain_non_literal_class (type);
+         if (complain & tf_error)
+           {
+             auto_diagnostic_group d;
+             error ("%qT is not a valid type for a template non-type parameter 
"
+                    "because it is not literal", type);
+             explain_non_literal_class (type);
+           }
          return true;
        }
       if (cp_has_mutable_p (type))
        {
-         error ("%qT is not a valid type for a template non-type parameter "
-                "because it has a mutable member", type);
+         if (complain & tf_error)
+           error ("%qT is not a valid type for a template non-type parameter "
+                  "because it has a mutable member", type);
          return true;
        }
       /* FIXME check op<=> and strong structural equality once spaceship is
-- 
2.18.1