Here when attempting to deduce T in the NTTP type A<T> from the argument
type 'const A<int>', we give up due to the const:
types ‘A<T>’ and ‘const A<int>’ have incompatible cv-qualifiers
But since the type of an NTTP cannot be cv-qualified, it seems natural
to ignore cv-qualifiers on the argument type before attempting to unify
the two types.
PR c++/105110
gcc/cp/ChangeLog:
* pt.cc (unify) <case TEMPLATE_PARM_INDEX>: Drop cv-quals from
the argument type of an NTTP before deducing from it.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/nontype-class52.C: New test.
&& !(strict & UNIFY_ALLOW_INTEGER)
&& TEMPLATE_PARM_LEVEL (parm) <= TMPL_ARGS_DEPTH (targs))
{
- /* Deduce it from the non-type argument. */
- tree atype = TREE_TYPE (arg);
+ /* Deduce it from the non-type argument. As above, ignore
+ top-level quals here too. */
+ tree atype = cv_unqualified (TREE_TYPE (arg));
RECUR_AND_CHECK_FAILURE (tparms, targs,
tparm, atype,
UNIFY_ALLOW_NONE, explain_p);
--- /dev/null
+// PR c++/105110
+// { dg-do compile { target c++20 } }
+
+template<class> struct A { };
+
+template<auto> struct B { };
+
+template<class T, A<T> V> void f(B<V>);
+
+int main() {
+ constexpr A<int> a;
+ f(B<a>{});
+}