[PATCH v1] libcamera: controls: Check size of enum

[Kieran Bingham]

Quoting Barnabás Pőcze (2025-03-10 17:02:54)
> Only enums whose sizes match that of `int32_t` can be directly
> supported. Otherwise the expected size and the real size would
> disagree, leading to an assertion failure in `ControlValue::set()`.
> 
> Signed-off-by: Barnabás Pőcze <barnabas.pocze at ideasonboard.com>

Has this happened? I assume if we try to make a control from an enum
where we override the type it would now produce a compile failure (which
I'm fine with for now).

I assume we could make similar mappings of other enum sizes if we needed
to at that point, but I don't see that as a requirement at the moment.

This looks positively defensive so:

Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>

We're in a public header, but I don't think this is an API breaking
change at all is it ? If this changed anything we'd see a compile
failure already...


> ---
>  include/libcamera/controls.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/libcamera/controls.h b/include/libcamera/controls.h
> index 7c7828ae5..4bfe9615c 100644
> --- a/include/libcamera/controls.h
> +++ b/include/libcamera/controls.h
> @@ -125,7 +125,7 @@ struct control_type<Span<T, N>> : public control_type<std::remove_cv_t<T>> {
>  };
>  
>  template<typename T>
> -struct control_type<T, std::enable_if_t<std::is_enum_v<T>>> : public control_type<int32_t> {
> +struct control_type<T, std::enable_if_t<std::is_enum_v<T> && sizeof(T) == sizeof(int32_t)>> : public control_type<int32_t> {
>  };
>  
>  } /* namespace details */
> -- 
> 2.48.1
>