postprocess-sdist-make-rust-ext-opt 0.1.2

Post-process sdists to make Rust extensions optional

postprocess-sdist-make-rust-ext-opt

This is a small tool to "post-process" Python source distributions ("sdists") containing setuptools-rust-based Rust extensions so that these extensions are marked as "optional" (cf. optional parameter in the setuptools-rust API docs).

What? Why?

What does it mean for an extension to be optional?

An extension (Rust or otherwise) being optional means that if the build fails when installing the package, the installation of the remainder of the package will proceed anyway and be considered successful. The package can then deal with the extension's absence at runtime, e.g. by providing pure-Python fallbacks for its functionality.

Why set it as optional in a postprocessing step and not from the start?

Because you'll probably want to build binary packages (wheels) from the project as well, but if your extension is marked as optional, any errors during their build will be ignored. So you don't generally want to have it set as optional when building wheels. It only really makes sense to have it set for the sdist, nothing else.

Why not do it the other way round?

Another option would be to set the extension as optional from the start but change it to non-optional before the wheel build. But the issue with that is that if you're using tools like setuptools-scm that automatically determine your package's version from its state as determined by a version control system (VCS) like Git, changing anything about the code will cause the version to be considered "dirty", which will be represented in the version string. A way to work around this would be to manipulate the VCS history in this case, but that is even more of a hack than the postprocessing.

Why not change it prior to building the sdist?

The same reason as above (dirty repo when building => modified automatically-determined version).

Installation

pip install postprocess-sdist-make-rust-ext-opt

Usage

$ postprocess-sdist-make-rust-ext-opt --help
Usage: postprocess-sdist-make-rust-ext-opt [OPTIONS] [SDIST_PATH]

Arguments:
  [SDIST_PATH]  [default: path of the sdist .tar.gz archive to post-process]

Options:
  --install-completion [bash|zsh|fish|powershell|pwsh]
                                  Install completion for the specified shell.
  --show-completion [bash|zsh|fish|powershell|pwsh]
                                  Show completion for the specified shell, to
                                  copy it or customize the installation.
  --help                          Show this message and exit.

The processed sdist will be written to a folder named postprocessed in the same directory as the input sdist. Its filename will be the same as that of the input sdist.

Caveats

The RustExtension calls for which the optional argument should be set to True must be placed directly inside the list that is assigned to the rust_extensions parameter of the top-level setup() call like so:

from setuptools import setup

setup(
    ...
    rust_extensions=[
        RustExtension(...),
    ]
    ...
)

Anything more indirect than that, e.g. assigning a RustExtension instance to a variable and then placing that inside the rust_extensions list, will cause the tool to exit with an error.

This is because the transformation is implemented at the syntax tree level and no static analysis is performed to trace arguments back to their origins.

Acknowledgements

The transformation is performed using RedBaron's full syntax tree (FST) representation of the sdist's setup.py.