[Bug c/109863] New: RFE: more consistent flex array initialization: lift static storage requirement in gnu2x

[Bug c/109863] New: RFE: more consistent flex array initialization: lift static storage requirement in gnu2x

[yann at droneaud dot fr]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109863

            Bug ID: 109863
           Summary: RFE: more consistent flex array initialization: lift
                    static storage requirement in gnu2x
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: yann at droneaud dot fr
  Target Milestone: ---

I've noted some discrepancies in the flex array initialization support:

    /* https://godbolt.org/z/9er5G9G15 */

    struct s { char i; char c[]; };

    extern void t(const struct s*);

    void f(void)
    {
        // ERROR: non-static initialization of a flexible array member
        const struct s c0 = { .c = "0", };
        t(&c0);

        // ERROR: non-static initialization of a flexible array member
        const struct s *const c1 = &(const struct s) { .c = "1", };
        t(c1);

        // OK
        const struct s *const c2 = &(constexpr struct s) { .c = "2", };
        t(c2);

        // ERROR: initializer element is not constant
        static const struct s *const c3 = &(constexpr struct s) { .c = "3", };
        t(c3);

        // OK
        static const struct s *const c4 = &(static constexpr struct s) { .c =
"4", };
        t(c4);
    }

AFAICT constexpr is not supposed to also mean static storage at the block
level, so flex array in c2 is initialized in a non-static way ...

Then I would be happy if GCC could be enhanced to not reject c0 and c1
initialization.

But I fear the opposite will happen, and GCC will reject c2 initialization too
:)

[Bug c/109863] RFE: more consistent flex array initialization: lift static storage requirement in gnu2x

[xry111 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109863

Xi Ruoyao <xry111 at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |xry111 at gcc dot gnu.org

--- Comment #1 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
Note that the entire "initializing a flexible array member" thing is a GNU
extension and not supported by the standard.  So GCC is free to support the
constexpr case but reject other non-static cases.

[Bug c/109863] RFE: more consistent flex array initialization: lift static storage requirement in gnu2x

[xry111 at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109863

--- Comment #2 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
(In reply to Xi Ruoyao from comment #1)
> Note that the entire "initializing a flexible array member" thing is a GNU
> extension and not supported by the standard.  So GCC is free to support the
> constexpr case but reject other non-static cases.

Or, "it's an extension after all, so it's not related to if the standard say
constexpr implies static or not".