[Bug c++/95486] New: ICE for alias CTAD with non-dependent argument and constrained constructor

[Bug c++/95486] New: ICE for alias CTAD with non-dependent argument and constrained constructor

[johelegp at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95486

            Bug ID: 95486
           Summary: ICE for alias CTAD with non-dependent argument and
                    constrained constructor
           Product: gcc
           Version: 10.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: johelegp at gmail dot com
  Target Milestone: ---

See https://godbolt.org/z/cPWdGW.
```C++
template<class>
concept Auto = true;

template<class T, class U>
struct X { constexpr X(const Auto auto) {} };

template<class U>
using Y = X<long, U>;

constexpr Y y{1};
```

[Bug c++/95486] ICE for alias CTAD with non-dependent argument and constrained constructor

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95486

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
                 CC|                            |jason at gcc dot gnu.org,
                   |                            |marxin at gcc dot gnu.org
   Last reconfirmed|                            |2020-06-03
             Status|UNCONFIRMED                 |WAITING

--- Comment #1 from Martin Liška <marxin at gcc dot gnu.org> ---
The ICE started with r10-5020-g1a291106384cabc7.
Is it a valid or invalid code?

[Bug c++/95486] ICE for alias CTAD with non-dependent argument and constrained constructor

[johelegp at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95486

--- Comment #2 from Johel Ernesto Guerrero Peña <johelegp at gmail dot com> ---
That commit added the feature I'm trying to use. I'd hope it's valid, or at
least with this other constructor added: `constexpr X(U) {}`.

[Bug c++/95486] ICE for alias CTAD with non-dependent argument and constrained constructor

[johelegp at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95486

--- Comment #3 from Johel Ernesto Guerrero Peña <johelegp at gmail dot com> ---
Having only the above unconstrained constructor works as expected, so I suppose
it's valid. See https://godbolt.org/z/nMysB_. The actual use case doesn't
currently have the unconstrained constructor, but does have a constrained
constructor and the ICE would prevent usage of the feature.

[Bug c++/95486] ICE for alias CTAD with non-dependent argument and constrained constructor

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95486

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |ice-on-valid-code
             Status|WAITING                     |UNCONFIRMED
     Ever confirmed|1                           |0

[Bug c++/95486] ICE for alias CTAD with non-dependent argument and constrained constructor

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95486

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ppalka at gcc dot gnu.org
   Last reconfirmed|2020-06-03 00:00:00         |2020-07-23
             Status|UNCONFIRMED                 |ASSIGNED
     Ever confirmed|0                           |1
           Assignee|unassigned at gcc dot gnu.org      |ppalka at gcc dot gnu.org

[Bug c++/95486] ICE for alias CTAD with non-dependent argument and constrained constructor

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95486

--- Comment #4 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:71141b1bd537cc516e485c834c2d36abba3f4544

commit r11-2419-g71141b1bd537cc516e485c834c2d36abba3f4544
Author: Patrick Palka <ppalka@redhat.com>
Date:   Wed Jul 29 22:06:41 2020 -0400

    c++: alias_ctad_tweaks and constrained dguide [PR95486]

    In the below testcase, we're ICEing from alias_ctad_tweaks ultimately
    because the implied deduction guide for X's user-defined constructor
    already has constraints associated with it.  We then carry over these
    constraints to 'fprime', the overlying deduction guide for the alias
    template Y, via tsubst_decl from alias_ctad_tweaks.  Later in
    alias_ctad_tweaks we call get_constraints followed by set_constraints
    without doing remove_constraints in between, which triggers the !found
    assert in set_constraints.

    This patch fixes this issue by adding an intervening call to
    remove_constraints.

    gcc/cp/ChangeLog:

            PR c++/95486
            * pt.c (alias_ctad_tweaks): Call remove_constraints before
            calling set_constraints.

    gcc/testsuite/ChangeLog:

            PR c++/95486
            * g++.dg/cpp2a/class-deduction-alias3.C: New test.

[Bug c++/95486] ICE for alias CTAD with non-dependent argument and constrained constructor

[johelegp at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95486

--- Comment #5 from Johel Ernesto Guerrero Peña <johelegp at gmail dot com> ---
Thank you. I was under the mistaken impression that the above was only a
partial solution. Adding the following deduction guide restores the ICE. See
https://godbolt.org/z/fej7WT.
```C++
template<class U>
X(U) -> X<char, U>;
```

[Bug c++/95486] ICE for alias CTAD with non-dependent argument and constrained constructor

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95486

--- Comment #6 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jason Merrill <jason@gcc.gnu.org>:

https://gcc.gnu.org/g:1a19d334ce493ec2ce2daeac74beef63fd67e2bc

commit r11-8104-g1a19d334ce493ec2ce2daeac74beef63fd67e2bc
Author: Jason Merrill <jason@redhat.com>
Date:   Fri Apr 9 18:02:38 2021 -0400

    c++: deduction guide using alias [PR99180]

    alias_ctad_tweaks was expecting that all deduction guides for the class
    would be suitable for deduction from the alias definition; in this case,
the
    deduction guide uses 'true' and the alias B uses 'false', so deduction
    fails.  But that's OK, we just don't use that deduction guide.  I also
    noticed that we were giving up on deduction entirely if substitution failed
    for some guide; we should only give up on that particular deduction guide.

    We ought to give a better diagnostic about this case when deduction fails,
    but that can wait.

    gcc/cp/ChangeLog:

            PR c++/99180
            PR c++/93295
            PR c++/93867
            PR c++/99118
            PR c++/96873
            * pt.c (alias_ctad_tweaks): Handle failure better.

    gcc/testsuite/ChangeLog:

            PR c++/99180
            PR c++/93295
            PR c++/93867
            PR c++/95486
            * g++.dg/cpp2a/class-deduction-alias5.C: New test.
            * g++.dg/cpp2a/class-deduction-alias6.C: New test.
            * g++.dg/cpp2a/class-deduction-alias7.C: New test.
            * g++.dg/cpp2a/class-deduction-alias8.C: New test.

[Bug c++/95486] ICE for alias CTAD with non-dependent argument and constrained constructor

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95486

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |11.0
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=93295

--- Comment #7 from Jason Merrill <jason at gcc dot gnu.org> ---
(In reply to Johel Ernesto Guerrero Peña from comment #5)
> Thank you. I was under the mistaken impression that the above was only a
> partial solution. Adding the following deduction guide restores the ICE. See
> https://godbolt.org/z/fej7WT.
> ```C++
> template<class U>
> X(U) -> X<char, U>;
> ```

That's bug 93295; let's leave this PR as the issue Patrick fixed.

[Bug c++/95486] ICE for alias CTAD with non-dependent argument and constrained constructor

[jason at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95486

Jason Merrill <jason at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |lnwirz at chem dot helsinki.fi

--- Comment #8 from Jason Merrill <jason at gcc dot gnu.org> ---
*** Bug 99675 has been marked as a duplicate of this bug. ***

[Bug c++/95486] ICE for alias CTAD with non-dependent argument and constrained constructor

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95486

--- Comment #9 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Patrick Palka
<ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:4806f9157a26cfd66c083bcc01596ff33009c0d6

commit r10-9743-g4806f9157a26cfd66c083bcc01596ff33009c0d6
Author: Patrick Palka <ppalka@redhat.com>
Date:   Wed Jul 29 22:06:41 2020 -0400

    c++: alias_ctad_tweaks and constrained dguide [PR95486]

    In the below testcase, we're ICEing from alias_ctad_tweaks ultimately
    because the implied deduction guide for X's user-defined constructor
    already has constraints associated with it.  We then carry over these
    constraints to 'fprime', the overlying deduction guide for the alias
    template Y, via tsubst_decl from alias_ctad_tweaks.  Later in
    alias_ctad_tweaks we call get_constraints followed by set_constraints
    without doing remove_constraints in between, which triggers the !found
    assert in set_constraints.

    This patch fixes this issue by adding an intervening call to
    remove_constraints.

    gcc/cp/ChangeLog:

            PR c++/95486
            * pt.c (alias_ctad_tweaks): Call remove_constraints before
            calling set_constraints.

    gcc/testsuite/ChangeLog:

            PR c++/95486
            * g++.dg/cpp2a/class-deduction-alias3.C: New test.

    (cherry picked from commit 71141b1bd537cc516e485c834c2d36abba3f4544)

[Bug c++/95486] ICE for alias CTAD with non-dependent argument and constrained constructor

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95486

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|11.0                        |10.4

--- Comment #10 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 10.4/11.

[Bug c++/95486] ICE for alias CTAD with non-dependent argument and constrained constructor

[johelegp at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95486

--- Comment #11 from Johel Ernesto Guerrero Peña <johelegp at gmail dot com> ---
Thank you. But the first CE link: https://godbolt.org/z/cPWdGW, and with the
addition in Comment 2: https://godbolt.org/z/Gezh5h5W4, they still ICE.

[Bug c++/95486] ICE for alias CTAD with non-dependent argument and constrained constructor

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95486

--- Comment #12 from Patrick Palka <ppalka at gcc dot gnu.org> ---
(In reply to Johel Ernesto Guerrero Peña from comment #11)
> Thank you. But the first CE link: https://godbolt.org/z/cPWdGW, and with the
> addition in Comment 2: https://godbolt.org/z/Gezh5h5W4, they still ICE.

Hmm, these CE links are still using 10.1.  These examples should compile fine
with a recent GCC built from the 10 release branch (which I don't think CE
provides unfortunately).

[Bug c++/95486] ICE for alias CTAD with non-dependent argument and constrained constructor

[johelegp at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95486

--- Comment #13 from Johel Ernesto Guerrero Peña <johelegp at gmail dot com> ---
You're right. I thought they were compiling against GCC trunk.

[Bug c++/95486] ICE for alias CTAD with non-dependent argument and constrained constructor

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95486

--- Comment #14 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Jason Merrill
<jason@gcc.gnu.org>:

https://gcc.gnu.org/g:92e9b2a995f718f1c2ab1cd0840b439c24d3535f

commit r10-9852-g92e9b2a995f718f1c2ab1cd0840b439c24d3535f
Author: Jason Merrill <jason@redhat.com>
Date:   Fri Apr 9 18:02:38 2021 -0400

    c++: deduction guide using alias [PR99180]

    alias_ctad_tweaks was expecting that all deduction guides for the class
    would be suitable for deduction from the alias definition; in this case,
the
    deduction guide uses 'true' and the alias B uses 'false', so deduction
    fails.  But that's OK, we just don't use that deduction guide.  I also
    noticed that we were giving up on deduction entirely if substitution failed
    for some guide; we should only give up on that particular deduction guide.

    We ought to give a better diagnostic about this case when deduction fails,
    but that can wait.

    gcc/cp/ChangeLog:

            PR c++/99180
            PR c++/93295
            PR c++/93867
            PR c++/99118
            PR c++/96873
            * pt.c (alias_ctad_tweaks): Handle failure better.

    gcc/testsuite/ChangeLog:

            PR c++/99180
            PR c++/93295
            PR c++/93867
            PR c++/95486
            * g++.dg/cpp2a/class-deduction-alias5.C: New test.
            * g++.dg/cpp2a/class-deduction-alias6.C: New test.
            * g++.dg/cpp2a/class-deduction-alias7.C: New test.
            * g++.dg/cpp2a/class-deduction-alias8.C: New test.