Re: libgpiod: rust bindings and bindgen issue with C enums

[Miguel Ojeda <miguel.ojeda.sandonis@xxxxxxxxx>]

On Tue, Nov 22, 2022 at 4:38 PM Bartosz Golaszewski <brgl@xxxxxxxx> wrote:
>
> ---
> The expression that defines the value of an enumeration constant shall
> be an integer constant expression that has a value representable as an
> int.
> ---
>
> and virtually all compilers store enum variables as signed integers,

I don't think this is true. Both GCC and Clang seem to pick an
unsigned one if possible (for the enum, not the constants), e.g.
https://godbolt.org/z/6zjzMdP3T. I assume bindgen is using the one
decided by clang.

Note that the quote of the standard is a constraint, i.e. the values
of the constants need to fit in an `int` (and the compiler is required
to issue a diagnostic if they don't, under `-Wpedantic` in GCC/Clang).

> As enums are naturally signed integers in the C world - can we somehow
> make bindgen default to c_int for all enum types?

This would be https://github.com/rust-lang/rust-bindgen/issues/1966,
where it has been suggested as an option (as well as the fact that the
constants are not being generated as `c_int`).

Cheers,
Miguel