https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116382
Bug ID: 116382
Summary: [modules] Importing NTTP of template type causes
recursive lazy load
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Keywords: rejects-valid
Severity: normal
Priority: P3
Component: c++
Assignee: nshead at gcc dot gnu.org
Reporter: nshead at gcc dot gnu.org
Blocks: 103524
Target Milestone: ---
Consider:
// a.cpp
module m:a;
template <typename> struct X {};
template <X<int> nttp> struct index {};
template struct index<{}>;
// m.cpp
export module m;
import :a;
With 'g++ -fmodules-ts -std=c++20 -S a.cpp m.cpp':
m.C:2:11: error: recursive lazy load
2 | import :a;
| ^
m.C:2:11: fatal error: failed to load pendings for ‘::X’
compilation terminated.
This error occurs even with '-fno-module-lazy'. The root cause seems to be the
following logic for streaming in NTTPs in 'trees_in::tree_node':
case tt_nttp_var:
/* An NTTP object. */
{
tree init = tree_node ();
tree name = tree_node ();
if (!get_overrun ())
{
res = get_template_parm_object (init, name);
int tag = insert (res);
dump (dumper::TREE)
&& dump ("Created nttp object:%d %N", tag, name);
}
}
break;
The call to 'get_template_parm_object' calls 'cp_finish_decl' which eventually
ends up performing name lookup on the as-yet unstreamed '::X' when processing
the initialiser, resulting in a call to 'lazy_load_pendings' which cannot be
done during streaming.
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103524
[Bug 103524] [meta-bug] modules issue
