[Mesa-dev] Lets talk about autotools

[Dylan Baker]

Quoting Mathieu Bridon (2018-09-20 08:34:31)
> On Thu, 2018-09-20 at 15:56 +0100, Eric Engestrom wrote:
> > On Thursday, 2018-09-20 15:28:09 +0100, Emil Velikov wrote:
> > > 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 ;-)
> > 
> > _Once_ for you, because you have everything already set up, but for
> > all
> > the new users this means that nothing will work out of the box,
> > they'll
> > need to understand each and every options and figure out what they
> > need
> > them set to, before they can even start.
> > 
> > That sounds like a huge step backwards to me :/
> 
> Meson has a great feature called… "features".
> 
> The way it works is you have options which can be either enabled,
> disabled or "auto".
> 
> This way, those optional parts of the build can be built automatically
> by default if the required dependencies are present, or skipped if not,
> which seems to be what you want.
> 
> However, meson then has a --auto-features option which allows build
> integrators to get deterministic, reproducible builds by removing the
> automatic enabling/disabling based on dependencies.
> 
> Which seems like it can reconcile what you and Emil want? :)
> 
> More details here:
> 
> http://mesonbuild.com/Build-options.html#features
> 
> As a build integrator myself at the Freedesktop SDK project, I would
> love Mesa to make good use of this.
> 
> We regularly have issues due to this automatic behaviour, because we
> forgot a dependency or added one by mistake.
> 
> 
> -- 
> Mathieu
> 

I'm planning to make use of these, because they're great! Just wanted to wait
until they're not a brand new feature :)

Dylan
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