[pushed] c++: Empty args for variadic concept [PR98717]

[Jason Merrill]

Nice when fixing a bug is as easy as removing incorrect checks.

gcc/cp/ChangeLog:

	PR c++/98717
	* constraint.cc (build_concept_check_arguments): Remove assert.
	(build_concept_check): Allow empty args.

gcc/testsuite/ChangeLog:

	PR c++/98717
	* g++.dg/cpp2a/concepts-variadic3.C: New test.
---
 gcc/cp/constraint.cc                            | 8 --------
 gcc/testsuite/g++.dg/cpp2a/concepts-variadic3.C | 7 +++++++
 2 files changed, 7 insertions(+), 8 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-variadic3.C

diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index 9049d087859..31e0fb5079a 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -1345,7 +1345,6 @@ build_concept_check_arguments (tree arg, tree rest)
     }
   else
     {
-      gcc_assert (rest != NULL_TREE);
       args = rest;
     }
   return args;
@@ -1444,13 +1443,6 @@ build_concept_check (tree target, tree args, tsubst_flags_t complain)
 tree
 build_concept_check (tree decl, tree arg, tree rest, tsubst_flags_t complain)
 {
-  if (arg == NULL_TREE && rest == NULL_TREE)
-    {
-      tree id = build_nt (TEMPLATE_ID_EXPR, decl, rest);
-      error ("invalid use concept %qE", id);
-      return error_mark_node;
-    }
-
   tree args = build_concept_check_arguments (arg, rest);
 
   if (standard_concept_p (decl))
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-variadic3.C b/gcc/testsuite/g++.dg/cpp2a/concepts-variadic3.C
new file mode 100644
index 00000000000..6fa7113e734
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-variadic3.C
@@ -0,0 +1,7 @@
+// PR c++/98717
+// { dg-do compile { target c++20 } }
+
+template<typename... T>
+concept True = true;
+
+static_assert(True<>);

base-commit: e6cc142ad99ab8d28581f4ce61056c9cce74dba3
-- 
2.27.0