[Bug c++/103672] New: using with template<template<class...> class> causes internal compiler error

[Bug c++/103672] New: using with template<template<class...> class> causes internal compiler error

[turtlefight at ymail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103672

            Bug ID: 103672
           Summary: using with template<template<class...> class> causes
                    internal compiler error
           Product: gcc
           Version: 11.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: turtlefight at ymail dot com
  Target Milestone: ---

The following example results in an internal compiler error.
It does compile fine with clang and msvc.

Example Code:

#include <functional>
#include <memory>

template<class T>
struct unique {
    auto operator()(auto&&... args) {
        return std::make_unique<T>(std::forward<decltype(args)>(args)...);
    }
};

template<template<class...> class T, class... Args>
using deduced_type = decltype(T{std::declval<Args>()...});

template<template<class> class F, template<class...> class T, class... Args>
auto make(Args&&... args) {
    return F<deduced_type<T, Args...>>{}(std::forward<Args>(args)...);
}

template<class A, class B>
struct Foo { Foo(A,B) {} };


int main(){
    auto foo_unique = make<unique, Foo>(1, 2);
}


Full Error Message:
<source>: In instantiation of 'auto make(Args&& ...) [with F = unique; T = Foo;
Args = {int, int}]':
<source>:24:40:   required from here
<source>:16:41: internal compiler error: in tsubst, at cp/pt.c:15632
   16 |     return F<deduced_type<T, Args...>>{}(std::forward<Args>(args)...);
      |            ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
0x21004e9 internal_error(char const*, ...)
        ???:0
0x7e96eb fancy_abort(char const*, int, char const*)
        ???:0
0xa5fde7 tsubst(tree_node*, tree_node*, int, tree_node*)
        ???:0
0xa5d3af tsubst(tree_node*, tree_node*, int, tree_node*)
        ???:0
0xa89b76 tsubst_template_args(tree_node*, tree_node*, int, tree_node*)
        ???:0
0xa5d954 tsubst(tree_node*, tree_node*, int, tree_node*)
        ???:0
0xa5eb8d tsubst(tree_node*, tree_node*, int, tree_node*)
        ???:0
0xa63a47 instantiate_decl(tree_node*, bool, bool)
        ???:0
0x904ebe maybe_instantiate_decl(tree_node*)
        ???:0
0x906980 mark_used(tree_node*, int)
        ???:0
0x819197 build_new_function_call(tree_node*, vec<tree_node*, va_gc,
vl_embed>**, int)
        ???:0
0xaca89c finish_call_expr(tree_node*, vec<tree_node*, va_gc, vl_embed>**, bool,
bool, int)
        ???:0
0xa29b8d c_parse_file()
        ???:0
0xbb6bb2 c_common_parse_file()
        ???:0


Godbolt Example: https://godbolt.org/z/rd4PdYrq8


What's interesting is that the code compiles without problems if a using
declaration is not used, e.g.:

template<template<class> class F, template<class...> class T, class... Args>
auto make(Args&&... args) {
    return
F<decltype(T{std::declval<Args>()...})>{}(std::forward<Args>(args)...);
}


Godbolt Example: https://godbolt.org/z/Pd3Mjs8rG

[Bug c++/103672] [10/11/12 Regression] using with template<template<class...> class> causes internal compiler error

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103672

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2021-12-13
           Keywords|                            |ice-on-valid-code
      Known to work|                            |10.2.0, 9.4.0
                 CC|                            |ppalka at gcc dot gnu.org
             Status|UNCONFIRMED                 |NEW
      Known to fail|                            |10.3.0, 11.1.0, 12.0
            Summary|using with                  |[10/11/12 Regression] using
                   |template<template<class...> |with
                   |class> causes internal      |template<template<class...>
                   |compiler error              |class> causes internal
                   |                            |compiler error
     Ever confirmed|0                           |1

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
This started to ICE on trunk with r11-6614

  c++: Fix ICE with CTAD in concept [PR98611]

It was also backported to 10.3 as r10-9635

[Bug c++/103672] [10/11/12 Regression] using with template<template<class...> class> causes internal compiler error

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103672

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2
   Target Milestone|---                         |10.4

[Bug c++/103672] [10/11/12 Regression] using with template<template<class...> class> causes internal compiler error

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103672

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=91911

--- Comment #2 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Closely related to PR91911 due to the use of CTAD + alias template

[Bug c++/103672] [10/11/12 Regression] using with template<template<class...> class> causes internal compiler error

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103672

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:09845ad7569bac27c3a1dc7b410d9df764d2ca06

commit r12-6773-g09845ad7569bac27c3a1dc7b410d9df764d2ca06
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu Jan 20 09:25:49 2022 -0500

    c++: CTAD inside alias template [PR91911, PR103672]

    In the first testcase below, when processing the alias template
    ConstSpanType, transparency of alias template specializations means we
    replace SpanType<T> with its instantiated definition.  But this
    instantiation lowers the level of the CTAD placeholder for span{T()} from
    2 to 1, and so the later instantiation of ConstSpanType<int> erroneously
    substitutes this CTAD placeholder with the template argument at level 1
    index 0, i.e. with int, before we get a chance to perform the CTAD.

    Although we represent CTAD placeholders as template parameters, we never
    actually want to replace them via tsubst.  So this patch adjusts tsubst
    to handle CTAD placeholders by simply substituting the template and
    returning a new CTAD placeholder.  Moreover, this means that the level
    of a CTAD placeholder doesn't matter, so we may as well give them all
    the same level.  This patch gives them the special level 0.

    The change in tsubst_decl removes a likely dead !CHECKING_P safeguard
    added in 2017, which would otherwise now get triggered for variables
    with CTAD placeholder types (since their level is 0).

            PR c++/91911
            PR c++/103672

    gcc/cp/ChangeLog:

            * pt.cc (keep_template_parm): Punt on a level 0 template parm.
            (tsubst_decl) <case VAR_DECL>: Remove !CHECKING_P safeguard.
            (tsubst) <case TEMPLATE_TYPE_PARM>: Handle CTAD placeholders
            specially.
            (make_auto_1): Add defaulted 'level' parameter.
            (make_template_placeholder): Pass 0 as 'level' to make_auto_1.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp1z/class-deduction101.C: New test.
            * g++.dg/cpp1z/class-deduction101a.C: New test.
            * g++.dg/cpp1z/class-deduction101b.C: New test.
            * g++.dg/cpp1z/class-deduction102.C: New test.
            * g++.dg/cpp1z/class-deduction102a.C: New test.
            * g++.dg/cpp1z/class-deduction102b.C: New test.
            * g++.dg/cpp1z/class-deduction103.C: New test.

[Bug c++/103672] [10/11 Regression] using with template<template<class...> class> causes internal compiler error

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103672

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[10/11/12 Regression] using |[10/11 Regression] using
                   |with                        |with
                   |template<template<class...> |template<template<class...>
                   |class> causes internal      |class> causes internal
                   |compiler error              |compiler error

--- Comment #4 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 12 so far.

[Bug c++/103672] [10/11 Regression] using with template<template<class...> class> causes internal compiler error

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103672

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |ppalka at gcc dot gnu.org

[Bug c++/103672] [10/11 Regression] using with template<template<class...> class> causes internal compiler error

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103672

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|10.4                        |10.5

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
GCC 10.4 is being released, retargeting bugs to GCC 10.5.

[Bug c++/103672] [10/11 Regression] using with template<template<class...> class> causes internal compiler error

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103672

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
   Target Milestone|10.5                        |12.0
         Resolution|---                         |FIXED

--- Comment #6 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 12+.  This doesn't seem suitable for backporting, and never
properly worked before anyway so it's hardly a regression.