RE: [PATCH v3 3/3] build: RFC - add support for optional dependencies

["Morten Brørup" <mb@smartsharesystems.com>]

> From: Bruce Richardson [mailto:bruce.richardson@intel.com]
> Sent: Wednesday, 20 December 2023 15.22
> 
> In order to remove more libraries from the mandatory list, we need to
> have support for optionally having a dependency from a driver or
> library
> to another driver or lib. This patch adds this support by adding a new
> optional_deps variable, the contents of which are added to the deps
> list
> if those optional dependencies are present in the build.
> 
> Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> ---
>  drivers/meson.build | 7 +++++++
>  lib/meson.build     | 7 +++++++
>  2 files changed, 14 insertions(+)
> 
> diff --git a/drivers/meson.build b/drivers/meson.build
> index 5ba534049a..af2d8da5a8 100644
> --- a/drivers/meson.build
> +++ b/drivers/meson.build
> @@ -127,6 +127,7 @@ foreach subpath:subdirs
>          includes = [include_directories(drv_path)]
>          # set up internal deps. Drivers can append/override as
> necessary
>          deps = std_deps
> +        optional_deps = []

(I'm a meson noob, so please bear with my stupid questions.)

Is a separate "optional_deps" necessary? If a driver has any of these dependencies, why can it not just add them to the "deps" in the driver's meson.build file?

Ohhh... It's the other way around: The driver only depends on the other (optional) lib if that other lib is enabled! Correct?

Either way, please add an in-line comment describing optional_deps in the meson.build file.

>          # ext_deps: Stores external library dependency got
>          # using dependency() (preferred) or find_library().
>          # For the find_library() case (but not with dependency()) we
> also
> @@ -168,6 +169,12 @@ foreach subpath:subdirs
>              # get dependency objs from strings
>              shared_deps = ext_deps
>              static_deps = ext_deps
> +            foreach d:optional_deps
> +                #if optional dep exists, add it to the deps list
> +                if is_variable('shared_rte_' + d)
> +                    deps += d
> +                endif
> +            endforeach
>              foreach d:deps
>                  if not build
>                      break

The same feedback also applies to the lib/meson.build changes.