[gcc r12-7861] c++: reject concept w/ multiple tparm lists [PR105067]

[gcc r12-7861] c++: reject concept w/ multiple tparm lists [PR105067]

[Patrick Palka]

https://gcc.gnu.org/g:23e57329c6516a81a8d3eb21b365ca8a0ec0c41b

commit r12-7861-g23e57329c6516a81a8d3eb21b365ca8a0ec0c41b
Author: Patrick Palka <ppalka@redhat.com>
Date:   Mon Mar 28 14:15:39 2022 -0400

    c++: reject concept w/ multiple tparm lists [PR105067]
    
    We weren't rejecting a concept declared with multiple template
    parameter lists.
    
            PR c++/105067
    
    gcc/cp/ChangeLog:
    
            * pt.cc (finish_concept_definition): Check that a concept is
            declared with exactly one template parameter list.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/cpp2a/concepts-err4.C: New test.

Diff:
---
 gcc/cp/pt.cc                               | 6 ++++++
 gcc/testsuite/g++.dg/cpp2a/concepts-err4.C | 6 ++++++
 2 files changed, 12 insertions(+)

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 3df509bbed0..cd07e48cb5a 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -28815,6 +28815,12 @@ finish_concept_definition (cp_expr id, tree init)
       return error_mark_node;
     }
 
+  if (current_template_depth > 1)
+    {
+      error_at (loc, "concept %qE has multiple template parameter lists", *id);
+      return error_mark_node;
+    }
+
   /* Initially build the concept declaration; its type is bool.  */
   tree decl = build_lang_decl_loc (loc, CONCEPT_DECL, *id, boolean_type_node);
   DECL_CONTEXT (decl) = current_scope ();
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-err4.C b/gcc/testsuite/g++.dg/cpp2a/concepts-err4.C
new file mode 100644
index 00000000000..57a96a095c7
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-err4.C
@@ -0,0 +1,6 @@
+// PR c++/105067
+// { dg-do compile { target c++20 } }
+
+template<class>
+template<class>
+concept C = true; // { dg-error "parameter list" }