[PATCH] build: check drivers class dependencies early

[Bruce Richardson]

On Tue, Aug 01, 2023 at 10:52:53AM +0200, David Marchand wrote:
> Drivers implementing a class of devices (for example, drivers/event)
> depend on the associated abstraction library (lib/eventdev).
> This dependency is expressed in the top level meson.build for this class
> (drivers/event/meson.build).
> 
> As we are making more libraries optional, custom constructs referencing
> the class dependencies in some drivers meson.build (event/dlb2) may break.
> 
> It would be possible to add more checks in those drivers meson.build but
> it is more straightforward to not even consider a driver meson.build when
> the class dependencies are not met.
> 
> Signed-off-by: David Marchand <david.marchand at redhat.com>
> ---
>  drivers/meson.build | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/meson.build b/drivers/meson.build
> index 74ae8cb96b..c375352e77 100644
> --- a/drivers/meson.build
> +++ b/drivers/meson.build
> @@ -70,6 +70,17 @@ foreach subpath:subdirs
>      else
>          class = subpath
>          subdir(class)
> +        skip_class = false
> +        foreach d:std_deps
> +            if not is_variable('shared_rte_' + d)
> +                skip_class = true
> +                message('Disabling all @1@ drivers: missing internal dependency "@0@"'
> +                        .format(d, class))
> +            endif
> +        endforeach
> +        if skip_class
> +            continue
> +        endif
>      endif
>  
>      # save class name on first occurrence

I like this approach. However, we do need something in the summary at the
end of the build too. Either:

* Single message stating all drivers of a given class are skipped
* (as now), message for each driver stating that it has been disabled

The former is nice as it gives us a shorter summary. The latter is nice
because it's consistent with what we have now.  Authors choice, which to go
for! :-)

Thanks.
/Bruce