[PATCH v1] libcamera: controls: Arrays of arrays are not supported

[Laurent Pinchart]

On Fri, Apr 25, 2025 at 10:21:44AM +0200, Barnabás Pőcze wrote:
> 2025. 04. 23. 21:29 keltezéssel, Laurent Pinchart írta:
> > Hi Barnabás,
> > 
> > Thank you for the patch.
> > 
> > The subject line should tell what the patch does.
> 
> "Disallow arrays of array" ?

Ack.

> > On Wed, Apr 23, 2025 at 03:02:14PM +0100, Kieran Bingham wrote:
> >> Quoting Barnabás Pőcze (2025-04-22 13:44:01)
> >>> Arrays of arrays, even arrays of strings, are not supported by
> >>> the current `ControlValue` mechanism, so disable them for now
> >>> to trigger comptime errors if attempts are made to use them.
> > 
> > s/comptime/compile-time/
> > 
> >> This sounds safer than discovering the fault at runtime!
> >>
> >> Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
> >>
> >>> Signed-off-by: Barnabás Pőcze <barnabas.pocze at ideasonboard.com>
> >>> ---
> >>>   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 326452540..427517a02 100644
> >>> --- a/include/libcamera/controls.h
> >>> +++ b/include/libcamera/controls.h
> >>> @@ -121,7 +121,7 @@ struct control_type<Point> {
> >>>   };
> >>>   
> >>>   template<typename T, std::size_t N>
> >>> -struct control_type<Span<T, N>> : public control_type<std::remove_cv_t<T>> {
> >>> +struct control_type<Span<T, N>, std::enable_if_t<control_type<std::remove_cv_t<T>>::size == 0>> : public control_type<std::remove_cv_t<T>> {
> > 
> > Maybe with a bit of line wrap,
> 
> Everything I tried looks bad, do you have something specific in mind?

Maybe

struct control_type<Span<T, N>, std::enable_if_t<control_type<std::remove_cv_t<T>>::size == 0>>
	: public control_type<std::remove_cv_t<T>> {

? It's not a big deal.

> > Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> > 
> >>>          static constexpr std::size_t size = N;
> >>>   };
> >>>   

-- 
Regards,

Laurent Pinchart