c++: variadic ttp constraint subsumption [PR99904]

Here we're crashing when level-lowering the variadic constraint C<Ts...>
on the template template parameter TT because tsubst_pack_expansion expects
processing_template_decl to be set during a partial substitution.

	PR c++/99904

gcc/cp/ChangeLog:

	* pt.c (is_compatible_template_arg): Set processing_template_decl
	around tsubst_constraint_info.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/concepts-ttp4.C: New test.

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 19e03369ffa654ec1a5fe4cabe84844075c9ed1a..1e52aa757e1b7165197758b17a5d24375251ac9c 100644 (file)
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -8230,8 +8230,10 @@ is_compatible_template_arg (tree parm, tree arg)
     {
       tree aparms = DECL_INNERMOST_TEMPLATE_PARMS (arg);
       new_args = template_parms_level_to_args (aparms);
+      ++processing_template_decl;
       parm_cons = tsubst_constraint_info (parm_cons, new_args,
                                          tf_none, NULL_TREE);
+      --processing_template_decl;
       if (parm_cons == error_mark_node)
         return false;
     }

diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-ttp4.C b/gcc/testsuite/g++.dg/cpp2a/concepts-ttp4.C
new file mode 100644 (file)
index 0000000..cf3e71e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-ttp4.C
@@ -0,0 +1,9 @@
+// PR c++/99904
+// { dg-do compile { target c++20 } }
+
+template<class... Ts> concept C = (Ts::value && ...);
+template<class... Ts> requires C<Ts...> struct A;
+template<class T> requires true struct B;
+template<template<class... Ts> requires C<Ts...> class TT> struct S;
+using ty1 = S<A>;
+using ty2 = S<B>; // { dg-error "constraint" } TT's constraints don't subsume B's