pyo3/generate-import-lib breaks cargo vendor and offline build

[tiran]

We are using cargo vendor to create self-contained downstream sdists and then CARGO_NET_OFFLINE=true to build packages. The approach works fine for PyO3-based projects with setuptools-rust or maturin, e.g. cryptography, pydantic-core, and jiter. However yesterday's release jiter 0.6.0 broke vendoring and offline builds.

$ tar xf jiter-0.6.0.tar.gz
$ cd jiter-0.6.0
$ mkdir -p .cargo
$ cargo vendor > .cargo/config.toml
$ CARGO_NET_OFFLINE=true python3 -m build
* Creating isolated environment: venv+pip...
* Installing packages in isolated environment:
  - maturin>=1,<2
* Getting build dependencies for sdist...
* Building sdist...
Running `maturin pep517 write-sdist --sdist-directory .../jiter-0.6.0/dist`
error: no matching package named `python3-dll-a` found
location searched: registry `crates-io`
required by package `pyo3-build-config v0.22.3`
    ... which satisfies dependency `pyo3-build-config = "^0.22.0"` (locked to 0.22.3) of package `jiter v0.6.0 (.../jiter-0.6.0/crates/jiter)`
    ... which satisfies path dependency `jiter` (locked to 0.6.0) of package `jiter-python v0.6.0 (.../jiter-0.6.0/crates/jiter-python)`
As a reminder, you're using offline mode (--offline) which can sometimes cause surprising resolution failures, if this error is too confusing you may wish to retry without the offline flag.
💥 maturin failed
  Caused by: Cargo metadata failed. Does your crate compile with `cargo build`?
  Caused by: `cargo metadata` exited with an error: 
Error: command ['maturin', 'pep517', 'write-sdist', '--sdist-directory', '.../jiter-0.6.0/dist'] returned non-zero exit status 1

ERROR Backend subprocess exited when trying to invoke build_sdist

$ ls -la vendor/python3-dll-a
ls: cannot access 'vendor/python3-dll-a': No such file or directory

I tracked the problem down to #145 and pyo3/generate-import-lib. The feature adds additional dependencies like python3-dll-a that are not visible to cargo vendor. The fix is trivial, re-add extension modules feature to crates/jiter-python/Cargo.toml and include the new feature. This makes the dependency visible to cargo.

# crates/jiter-python/Cargo.toml
[features]
extension-module = ["pyo3/extension-module", "pyo3/generate-import-lib"]