[Bug c++/115085] New: Variable unqualified-id is falsely treated as rvalue when appearing in braced-init-list

[Bug c++/115085] New: Variable unqualified-id is falsely treated as rvalue when appearing in braced-init-list

[janschultke at googlemail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115085

            Bug ID: 115085
           Summary: Variable unqualified-id is falsely treated as rvalue
                    when appearing in braced-init-list
           Product: gcc
           Version: 15.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: janschultke at googlemail dot com
  Target Milestone: ---

> int a{}, b = decltype((a)){a};

GCC falsely rejects this (https://godbolt.org/z/a6c4h8Mhv).
If you're having trouble reading this, it also rejects:

> using T = int&;
> int a{}, b = T{a};

Splitting this into multiple lines is also not relevant. The error is:

> <source>:3:17: error: cannot bind non-const lvalue reference of type 'T' {aka 'int&'} to an rvalue of type 'int'
>    3 | int a{}, b = T{a};
>      |                 ^

There is no apparent reason why should be an rvalue in this context. It is not
move-eligible within the initializer of a variable.

My guess is something something aggregate initialization doing
copy-initialization for each initializer and then getting a prvalue out of
that. Dunno, it's quite weird.

See https://stackoverflow.com/a/78477064/5740428 for a more in-depth
explanation of the relevant wording.

[Bug c++/115085] Variable unqualified-id is falsely treated as rvalue when appearing in braced-init-list

[janschultke at googlemail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115085

--- Comment #1 from Jan Schultke <janschultke at googlemail dot com> ---
Another user suggested that this is caused by falsely performing temporary
materialization.

This would make a an xvalue, which would also make the reference binding fail.

[Bug c++/115085] Variable unqualified-id is falsely treated as rvalue when appearing in braced-init-list

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115085

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I think there is a dup of this bug already filed ...

[Bug c++/115085] Variable unqualified-id is falsely treated as rvalue when appearing in braced-init-list

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115085

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
See https://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#1521 also.

[Bug c++/115085] Variable unqualified-id is falsely treated as rvalue when appearing in braced-init-list

[janschultke at googlemail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115085

--- Comment #4 from Jan Schultke <janschultke at googlemail dot com> ---
https://github.com/cplusplus/CWG/issues/536

[Bug c++/115085] Variable unqualified-id is falsely treated as rvalue when appearing in braced-init-list

[jlame646 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115085

Jason Liam <jlame646 at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jlame646 at gmail dot com

--- Comment #5 from Jason Liam <jlame646 at gmail dot com> ---
Maybe related bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64892

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78209