Here, when unifying TT with S, processing_template_decl is unset, and
this foils the dependence checks in do_auto_deduction for avoiding
checking constraints on an auto when the initializer is dependent.
This patch fixes this issue by making sure processing_template_decl is
set during the call to unify from coerce_template_template_parms; this
seems sensible because we're unifying one set of template parameters
with another, so we're dealing with templated trees throughout.
Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
trunk?
PR c++/99909
gcc/cp/ChangeLog:
* pt.c (coerce_template_template_parms): Keep
processing_template_decl set during the call to unify as well.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/concepts-ttp3.C: New test.
---
gcc/cp/pt.c | 4 ++--
gcc/testsuite/g++.dg/cpp2a/concepts-ttp3.C | 11 +++++++++++
2 files changed, 13 insertions(+), 2 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-ttp3.C
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 41fa7ed5e43..1dcdffe322a 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -7994,12 +7994,12 @@ coerce_template_template_parms (tree parm_parms,
/* So coerce P's args to apply to A's parms, and then deduce between A's
args and the converted args. If that succeeds, A is at least as
specialized as P, so they match.*/
+ processing_template_decl_sentinel ptds (/*reset*/false);
+ ++processing_template_decl;
tree pargs = template_parms_level_to_args (parm_parms);
pargs = add_outermost_template_args (outer_args, pargs);
- ++processing_template_decl;
pargs = coerce_template_parms (arg_parms, pargs, NULL_TREE, tf_none,
/*require_all*/true, /*use_default*/true);
- --processing_template_decl;
if (pargs != error_mark_node)
{
tree targs = make_tree_vec (nargs);
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-ttp3.C
b/gcc/testsuite/g++.dg/cpp2a/concepts-ttp3.C
new file mode 100644
index 00000000000..898524e0dfa
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-ttp3.C
@@ -0,0 +1,11 @@
+// PR c++/99909
+// { dg-do compile { target c++20 } }
+
+template<class T> constexpr bool always_true = true;
+template<class T> concept C = always_true<T>;
+
+template<C auto> struct S { };
+
+template<template<auto> class TT> void f() { }
+
+template void f<S>();
--
2.33.0.591.gddb1055343
