From: Patrick Palka <ppalka@redhat.com>
Date: Sun, 7 May 2023 16:05:24 +0000 (-0400)
Subject: c++: satisfaction of non-dep member alias template-id
X-Git-Tag: basepoints/gcc-15~9577
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b28a7c41fb4697b2d5d9e6e6552b0764bd7d90f0;p=thirdparty%2Fgcc.git

c++: satisfaction of non-dep member alias template-id

constraints_satisfied_p already carefully checks dependence of template
arguments before proceeding with satisfaction, so the dependence check
in instantiate_alias_template is unnecessary and overly conservative.
Getting rid of it allows us to check satisfaction ahead of time in more
cases as in the below testcase.

gcc/cp/ChangeLog:

	* pt.cc (instantiate_alias_template): Exit early upon
	error from coerce_template_parms.  Remove dependence test
	guarding constraints_satisfied_p.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/concepts-alias6.C: New test.
---

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index bb4e275d714b..d400b9f3eb25 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -22181,11 +22181,11 @@ instantiate_alias_template (tree tmpl, tree args, tsubst_flags_t complain)
 
   args = coerce_template_parms (DECL_TEMPLATE_PARMS (tmpl),
 				args, tmpl, complain);
+  if (args == error_mark_node)
+    return error_mark_node;
 
   /* FIXME check for satisfaction in check_instantiated_args.  */
-  if (flag_concepts
-      && !any_dependent_template_arguments_p (args)
-      && !constraints_satisfied_p (tmpl, args))
+  if (!constraints_satisfied_p (tmpl, args))
     {
       if (complain & tf_error)
 	{
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-alias6.C b/gcc/testsuite/g++.dg/cpp2a/concepts-alias6.C
new file mode 100644
index 000000000000..55f25a7ccf80
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-alias6.C
@@ -0,0 +1,15 @@
+// Verify we can check satisfaction of a non-dependent member alias
+// template-id whose constraints don't depend on outer template
+// parameters ahead of time.
+// { dg-do compile { target c++20 } }
+
+template<class T>
+struct A {
+  template<int N> requires (N > 0)
+  using at = T;
+
+  void f() {
+    using ty1 = at<0>; // { dg-error "constraint" }
+    using ty2 = at<1>;
+  }
+};