TST: add Rust extension module using PyO3

[dnicolodi]

No description provided.

[dnicolodi]

This almost works with unreleased Meson 1.12.0 and nightly Rust toolchain. The missing bit is translating the build.rs in pyo3-ffi into an equivalent meson.build. @bonzini did a first attempt, but either I didn't integrate it properly or there is a bug. I'll open another PR with a test package using the Python C API directly from Rust.

[bonzini]

It did what it was intending to do:

"--check-cfg" "cfg(pyo3_use_raw_dylib)" "--check-cfg" "cfg(pyo3_dll,values(any()))" "--cfg" "pyo3_use_raw_dylib" "--cfg" "pyo3_dll=\"python312.dll\""

It clearly needs more work to exactly match build.rs, possibly by someone that does have access to a Windows toolchain unlike you and I...

[dnicolodi]

As I was mentioning in the related issue, I get a segmentation fault on macOS when the extension module raises an error. I don't get the segfault when compiling with maturin. Thus there is something off in the compilation on macOS too. I haven't had time to investigate a way to compare the output of build.rs with the configuration generated by Meson.

[lucascolley]

As I was mentioning in the related issue, I get a segmentation fault on macOS when the extension module raises an error.

How to reproduce? It seems fine for me on osx-arm64:

>>> rust_pyo3.sum(1, 2.0)
Traceback (most recent call last):
  File "<python-input-6>", line 1, in <module>
    rust_pyo3.sum(1, 2.0)
    ~~~~~~~~~~~~~^^^^^^^^
TypeError: 'float' object cannot be interpreted as an integer
while processing 'b'

[bonzini]

Ot just what are the missing flags from build.rs on macOS?

[dnicolodi]

I compared the cargo:rustc-cfg= lines emitted by build.rs with the --cfg options appended to extra_flags by meson.build and neglected everything else. I added this to meson.build:

extra_args += [
  '--cfg', 'cfg_select',
  '--cfg', 'const_is_null',
  '--cfg', 'fn_ptr_eq',
  '--cfg', 'from_bytes_with_nul_error',
]

I didn't check what these are for.

I cannot reproduce the segmentation fault now... With my knowledge of Rust and associated tooling and working on this in bits and pieces in between other things I probably made a mistake somewhere...

[lucascolley]

I can possibly debug on windows in a few days' time, if someone can tell me roughly what to look for.

[bonzini]

Ok, those are easy as they are simply based on the rustc version.

https://github.com/PyO3/pyo3/blob/2e49529008277e11419ac4572ef03c441b604f77/pyo3-build-config/src/lib.rs#L270