From: Patrick Palka <ppalka@redhat.com>
Date: Wed, 18 Aug 2021 12:37:42 +0000 (-0400)
Subject: c++: ignore explicit dguides during NTTP CTAD [PR101883]
X-Git-Tag: releases/gcc-11.3.0~815
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=52dd840c5eba25ef54dee3f1c78f371032a7c051;p=thirdparty%2Fgcc.git

c++: ignore explicit dguides during NTTP CTAD [PR101883]

Since (template) argument passing is a copy-initialization context,
we mustn't consider explicit deduction guides when deducing a CTAD
placeholder type of an NTTP.

	PR c++/101883

gcc/cp/ChangeLog:

	* pt.c (convert_template_argument): Pass LOOKUP_IMPLICIT to
	do_auto_deduction.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/nontype-class49.C: New test.

(cherry picked from commit a6b3db3e8625a3cba1240f0b5e1a29bd6c68b8ca)
---

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 45f39ab7fff6..077097d91753 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -8514,7 +8514,8 @@ convert_template_argument (tree parm,
 	   can happen in the context of -fnew-ttp-matching.  */;
       else if (tree a = type_uses_auto (t))
 	{
-	  t = do_auto_deduction (t, arg, a, complain, adc_unify, args);
+	  t = do_auto_deduction (t, arg, a, complain, adc_unify, args,
+				 LOOKUP_IMPLICIT);
 	  if (t == error_mark_node)
 	    return error_mark_node;
 	}
diff --git a/gcc/testsuite/g++.dg/cpp2a/nontype-class49.C b/gcc/testsuite/g++.dg/cpp2a/nontype-class49.C
new file mode 100644
index 000000000000..c83e4075ed07
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/nontype-class49.C
@@ -0,0 +1,8 @@
+// PR c++/101883
+// { dg-do compile { target c++20 } }
+
+template<class T> struct C { constexpr C(int) { } };
+explicit C(int) -> C<int>;
+
+template<C c> struct X { };
+X<1> x; // { dg-error "deduction|no match" }