Re: [RFC PATCH v3 2/5] rust: add bindgen step as a meson dependency

[Stefan Hajnoczi]

On Thu, 20 Jun 2024 at 14:35, Manos Pitsidianakis
<manos.pitsidianakis@linaro.org> wrote:
>
> On Thu, 20 Jun 2024 15:32, Alex Bennée <alex.bennee@linaro.org> wrote:
> >Manos Pitsidianakis <manos.pitsidianakis@linaro.org> writes:
> >
> >> Add mechanism to generate rust hw targets that depend on a custom
> >> bindgen target for rust bindings to C.
> >>
> >> This way bindings will be created before the rust crate is compiled.
> >>
> >> The bindings will end up in BUILDDIR/{target}-generated.rs and have the 
> >> same name
> >> as a target:
> >>
> >> ninja aarch64-softmmu-generated.rs
> >>
> ><snip>
> >> +
> >> +
> >> +rust_targets = {}
> >> +
> >> +cargo_wrapper = [
> >> +  find_program(meson.global_source_root() / 'scripts/cargo_wrapper.py'),
> >> +  '--config-headers', meson.project_build_root() / 'config-host.h',
> >> +  '--meson-build-root', meson.project_build_root(),
> >> +  '--meson-build-dir', meson.current_build_dir(),
> >> +  '--meson-source-dir', meson.current_source_dir(),
> >> +]
> >
> >I'm unclear what the difference between meson-build-root and
> >meson-build-dir is?
>
> Build-dir is the subdir of the current subdir(...) meson.build file
>
> So if we are building under qemu/build, meson_build_root is qemu/build
> and meson_build_dir is qemu/build/rust
>
> >
> >We also end up defining crate-dir and outdir. Aren't these all
> >derivable from whatever module we are building?
>
> Crate dir is the source directory (i.e. qemu/rust/pl011) that contains
> the crate's manifest file Cargo.toml.
>
> Outdir is where to put the final build artifact for meson to find. We
> could derive that from the build directories and package names somehow
> but I chose to be explicit instead of doing indirect logic to make the
> process less magic.
>
> I know it's a lot so I'm open to simplifications. The only problem is
> that all of these directories, except the crate source code, are defined
> from meson and can change with any refactor we do from the meson side of
> things.

Expanding the help text for these command-line options would make it
easier to understand. It would be great to include an example path
too.

Stefan