From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
	id D270B3858D34; Thu, 15 Aug 2024 12:10:59 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org D270B3858D34
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1723723859;
	bh=/ATb+HwLwSrfCknDXX4BtMxFBa2Tqk2vpJMryLDjudI=;
	h=From:To:Subject:Date:From;
	b=y1nvH1aoSZFp6Kys2iZRJXWCTO58r3M/FstgfJmpaUg2krtK/P7zgGiBD/84TDuQX
	 AR8NXl3KmLqAqcB6vL5Ih5FQ0LnF4x4UhckenodSRj6ipc1PqLSC6aUwlQO5t+69wB
	 8ktBG3HPTvNm3XDh9dS7IICG9LjXmI2TPz7Sdorg=
From: "nshead at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/116382] New: [modules] Importing NTTP of template type
 causes recursive lazy load
Date: Thu, 15 Aug 2024 12:10:59 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Version: 15.0
X-Bugzilla-Keywords: rejects-valid
X-Bugzilla-Severity: normal
X-Bugzilla-Who: nshead at gcc dot gnu.org
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: nshead at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: bug_id short_desc product version bug_status
 keywords bug_severity priority component assigned_to reporter blocked
 target_milestone
Message-ID: <bug-116382-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
List-Id: <gcc-bugs.sourceware.org>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D116382

            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=3Dc++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 =E2=80=98::X=E2=80=99
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 =3D tree_node ();
        tree name =3D tree_node ();
        if (!get_overrun ())
          {
            res =3D get_template_parm_object (init, name);
            int tag =3D 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 eventua=
lly
ends up performing name lookup on the as-yet unstreamed '::X' when processi=
ng
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=3D103524
[Bug 103524] [meta-bug] modules issue=