[gcc r12-6697] c++: DEPENDENT_OPERATOR_TYPE as type of NTTP [PR104074]

[gcc r12-6697] c++: DEPENDENT_OPERATOR_TYPE as type of NTTP [PR104074]

[Patrick Palka]

https://gcc.gnu.org/g:3c4a54adb2164315d18fd8980c0fc37eb3d22252

commit r12-6697-g3c4a54adb2164315d18fd8980c0fc37eb3d22252
Author: Patrick Palka <ppalka@redhat.com>
Date:   Tue Jan 18 14:50:06 2022 -0500

    c++: DEPENDENT_OPERATOR_TYPE as type of NTTP [PR104074]
    
    We're incorrectly rejecting the below testcase during template argument
    coercion because invalid_nontype_parm_type_p returns true for
    DEPENDENT_OPERATOR_TYPE in C++17 mode.
    
    This patch fixes this by partially rewriting invalid_nontype_parm_type_p
    in terms of WILDCARD_TYPE_P, for which DEPENDENT_OPERATOR_TYPE is true,
    so that the predicate handles wildcard types consistently.
    
            PR c++/104074
    
    gcc/cp/ChangeLog:
    
            * pt.cc (invalid_nontype_parm_type_p): Use WILDCARD_TYPE_P so
            that we return false for DEPENDENT_OPERATOR_TYPE too.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/cpp1z/nontype-auto20.C: New test.

Diff:
---
 gcc/cp/pt.cc                                | 14 ++++++--------
 gcc/testsuite/g++.dg/cpp1z/nontype-auto20.C |  5 +++++
 2 files changed, 11 insertions(+), 8 deletions(-)

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 4a2b33ec940..586ad1c97f6 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -26931,16 +26931,14 @@ invalid_nontype_parm_type_p (tree type, tsubst_flags_t complain)
 	}
       return false;
     }
-  else if (TREE_CODE (type) == TYPENAME_TYPE)
-    return false;
-  else if (TREE_CODE (type) == DECLTYPE_TYPE)
-    return false;
   else if (TREE_CODE (type) == NULLPTR_TYPE)
     return false;
-  /* A bound template template parm could later be instantiated to have a valid
-     nontype parm type via an alias template.  */
-  else if (cxx_dialect >= cxx11
-	   && TREE_CODE (type) == BOUND_TEMPLATE_TEMPLATE_PARM)
+  else if (TREE_CODE (type) == BOUND_TEMPLATE_TEMPLATE_PARM
+	   && cxx_dialect < cxx11)
+    /* Fall through; before C++11 alias templates, a bound ttp
+       always instantiates into a class type.  */;
+  else if (WILDCARD_TYPE_P (type))
+    /* Any other wildcard type not already handled above is allowed.  */
     return false;
   else if (TREE_CODE (type) == COMPLEX_TYPE)
     /* Fall through.  */;
diff --git a/gcc/testsuite/g++.dg/cpp1z/nontype-auto20.C b/gcc/testsuite/g++.dg/cpp1z/nontype-auto20.C
new file mode 100644
index 00000000000..87a2a5fb9f7
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1z/nontype-auto20.C
@@ -0,0 +1,5 @@
+// PR c++/104074
+// { dg-do compile { target c++17 } }
+
+template<auto> class gr_sp;
+template<class T> using gr_rp = gr_sp<T::value + 42>;