[Bug c++/112410] New: error when auto(x) is used in a variable initializer

[Bug c++/112410] New: error when auto(x) is used in a variable initializer

[vanyacpp at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112410

            Bug ID: 112410
           Summary: error when auto(x) is used in a variable initializer
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vanyacpp at gmail dot com
  Target Milestone: ---

int x = auto(42); // OK
int y(auto(42));  // error

On the second line GCC -std=c++23 gives an error:

error: non-function 'y' declared as implicit template

I believe the code is correct and should compile without errors.

[Bug c++/112410] error when auto(x) is used in a variable initializer

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112410

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
                 CC|                            |mpolacek at gcc dot gnu.org
   Last reconfirmed|                            |2023-11-06
             Status|UNCONFIRMED                 |NEW

--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
I think you're right.  Same for

int z(auto{42});

[Bug c++/112410] error when auto(x) is used in a variable initializer

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112410

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.

Looks like GCC is messing the Most vexing parse here.

[Bug c++/112410] error when auto(x) is used in a variable initializer

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112410

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

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

--- Comment #3 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Part of the problem seems to be that fully_implicit_function_template_p is set.
 I'd like to poke more.

[Bug c++/112410] error when auto(x) is used in a variable initializer

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112410

--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The trunk branch has been updated by Marek Polacek <mpolacek@gcc.gnu.org>:

https://gcc.gnu.org/g:70060dadfbf0d0af5f4cab5f3aff3223a4523606

commit r14-5514-g70060dadfbf0d0af5f4cab5f3aff3223a4523606
Author: Marek Polacek <polacek@redhat.com>
Date:   Thu Nov 9 12:25:25 2023 -0500

    c++: fix parsing with auto(x) [PR112410]

    Here we are wrongly parsing

      int y(auto(42));

    which uses the C++23 cast-to-prvalue feature, and initializes y to 42.
    However, we were treating the auto as an implicit template parameter.

    Fixing the auto{42} case is easy, but when auto is followed by a (,
    I found the fix to be much more involved.  For instance, we cannot
    use cp_parser_expression, because that can give hard errors.  It's
    also necessary to disambiguate 'auto(i)' as 'auto i', not a cast.
    auto(), auto(int), auto(f)(int), auto(*), auto(i[]), auto(...), etc.
    are all function declarations.

    This patch rectifies that by undoing the implicit function template
    modification.  In the test above, we should notice that the parameter
    list is ill-formed, and since we've synthesized an implicit template
    parameter, we undo it by calling abort_fully_implicit_template.  Then,
    we'll parse the "(auto(42))" as an initializer.

            PR c++/112410

    gcc/cp/ChangeLog:

            * parser.cc (cp_parser_direct_declarator): Maybe call
            abort_fully_implicit_template if it turned out the parameter list
was
            ill-formed.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp23/auto-fncast13.C: New test.
            * g++.dg/cpp23/auto-fncast14.C: New test.

[Bug c++/112410] error when auto(x) is used in a variable initializer

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112410

--- Comment #5 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Fixed on trunk so far; I want to fix it in 13 too.

[Bug c++/112410] error when auto(x) is used in a variable initializer

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112410

--- Comment #6 from GCC Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-13 branch has been updated by Marek Polacek
<mpolacek@gcc.gnu.org>:

https://gcc.gnu.org/g:60979215517629400902938b1c5666f97d0653cf

commit r13-8147-g60979215517629400902938b1c5666f97d0653cf
Author: Marek Polacek <polacek@redhat.com>
Date:   Thu Nov 9 12:25:25 2023 -0500

    c++: fix parsing with auto(x) [PR112410]

    Here we are wrongly parsing

      int y(auto(42));

    which uses the C++23 cast-to-prvalue feature, and initializes y to 42.
    However, we were treating the auto as an implicit template parameter.

    Fixing the auto{42} case is easy, but when auto is followed by a (,
    I found the fix to be much more involved.  For instance, we cannot
    use cp_parser_expression, because that can give hard errors.  It's
    also necessary to disambiguate 'auto(i)' as 'auto i', not a cast.
    auto(), auto(int), auto(f)(int), auto(*), auto(i[]), auto(...), etc.
    are all function declarations.

    This patch rectifies that by undoing the implicit function template
    modification.  In the test above, we should notice that the parameter
    list is ill-formed, and since we've synthesized an implicit template
    parameter, we undo it by calling abort_fully_implicit_template.  Then,
    we'll parse the "(auto(42))" as an initializer.

            PR c++/112410

    gcc/cp/ChangeLog:

            * parser.cc (cp_parser_direct_declarator): Maybe call
            abort_fully_implicit_template if it turned out the parameter list
was
            ill-formed.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp23/auto-fncast13.C: New test.
            * g++.dg/cpp23/auto-fncast14.C: New test.

    (cherry picked from commit 70060dadfbf0d0af5f4cab5f3aff3223a4523606)

[Bug c++/112410] error when auto(x) is used in a variable initializer

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112410

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #7 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Fixed.