[Mesa-dev] Lets talk about autotools

[Emil Velikov]

Hi Chuck,

On 18 September 2018 at 16:00, Chuck Atkins <chuck.atkins at kitware.com> wrote:
> First, I'm fully in support of killing off autotools woo-hoo to that.  And
> given the substantial investment already put into the meson build that
> certainly seems like a good direction to go.
>
> That being said, the way "auto" is currently implemented leaves quite a bit
> to be desired.  One of the nice features of the Autotools build was how
> auto-enabled options were treated in that the dependencies were searched for
> and if they were all found and met then the option would be enabled.  My
> experience so far with the meson build has shown this not to be the case and
> a "configure" with no options has yet to be successful for me.  Many of the
> 'auto' options are treated as 'set to true if your platform supports it'
> regardless of whether your system has the requisite dependencies available.
> For example"
>
> The 'gallium-va' option defaults to 'auto' but the implementation ends up
> setting the '_va' option to true if the other option conditions are met,
> long before libva is searched for.  So then when libva isn't found one gets
> an error.
>
> if set to auto then missing the libva dependencies should be a failure, it
> should just disable the gallium va state tracker
>
> The platform options set to 'auto'  has a set of checks to determine which
> platforms are enabled as required.  If the system_has_kms_drm check is true
> then Wayland is enabled as required.  Later if the check for wayland
> dependencies fails, an error occurs.
>
> If platforms are set to auto then a failure to locate dependencies for a
> given platform should disable the platform.
>
> I realize these are just two specific examples, each of which can be readily
> dealt with in their own specific way so I'm not asking "how to I address #1
> and #2?" because I can certainly do that.  These are just two instances of
> many though in the way "auto" is dealt with.  My point is really a broader
> one that before meson becomes the primary build then the behavior of "auto"
> should create a successful configure out of the box without additional
> options.
>
I would like to revive an idea from a few years ago:
Drop the "auto" all-together.

It adds a _ton_ of complexity while making the build semi-magical/not
as deterministic.
IIRC the Gnome people have been actively working for removing such
autodetection in their packages.

The only downside is that we may need to tweak our scripts _once_ to
list exactly what we want to build ;-)
Distributions already explicitly specify what they want and most of
our autodetection is effectively a bad copy of that.

HTH
Emil