[Mesa-dev] Rust drivers in Mesa

[Jason Ekstrand]

On Thu, Oct 1, 2020 at 10:56 PM Rob Clark <robdclark at gmail.com> wrote:
>
> On Thu, Oct 1, 2020 at 6:36 PM Alyssa Rosenzweig
> <alyssa.rosenzweig at collabora.com> wrote:
> >
> > Implications for the build system vary. Rust prefers to be built by its
> > own package manager, Cargo, which is tricky to integrate with other
> > build systems. Actually, Meson has native support for Rust, invoking the
> > compiler directly and skipping Cargo, as if it were C code. This support
> > is not widely adopted as it prevents linking with external libraries
> > ("crates", in Rust parlance), with discussions between Rust and Meson
> > developers ending in a stand-still [1]. For Mesa, this might be just
> > fine. Our out-of-tree run-time dependencies are minimal for the C code,
> > and Rust's standard library largely avoids the need for us to maintain a
> > Rust version of util/ in-tree. If this proves impractical in the
> > long-term, it is possible to integrate Cargo with Meson on our end [2].
> >
>
> drive-by comment: for something like a gl driver that a lot of other
> things depend on, making it harder for us to depend on other external
> things is actually a good thing

Generally, I'm a fan in concept.  Generally, I feel like rust has most
of what I like from C++ without most of what I don't like.  I
particularly like it's error handling mechanism, for instance.  That
said, when it comes to things like the borrow checker, my little bit
of rust experience says that it doesn't actually remove bugs so much
as move them around.

What's been stopping me is practicalities.  Not only build systems but
the way in which everything in mesa is interconnected.  Your
suggestion for building the entire back-end compiler with C-wrapped
helpers for NIR->compiler translation may be workable.  We might also
be able to write NIR wrappers sufficient for reading NIR.  It's not
actually that much API surface if all you want to do is read the data
structure.

I've also thought of breaking off a component like ISL and converting
it.  However, all the nicely contained pieces are also the ones that
wouldn't benefit as much. :-/

--Jason