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

[Manos Pitsidianakis <manos.pitsidianakis@linaro.org>]

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.