We have a common pattern here in nixpkgs for Python applications: when a
Python package ships with either a requirements.txt or setup.py file, we
generally end up having to modify its version restriction, otherwise we have
build failures since we package only one specific version of each package
normally.
However, this end up being done in a completely ad-hoc way: some people
use substituteInPlace, some others use sed, others uses patches, etc.
In many cases, the code ends up being buggy, so it may work in one
version and breaks on the next one. We can instead implement one
standard way of doing this, and trying to be a correct as possible.
So this is what this commit does: it implements a new build hook, that
when called will automatically patch the wheel file. This is one of the
most generic ways to patch Python dependencies, and should work in
multiple cases.
This commit splits the `buildPythonPackage` into multiple setup hooks.
Generally, Python packages are built from source to wheels using `setuptools`.
The wheels are then installed with `pip`. Tests were often called with
`python setup.py test` but this is less common nowadays. Most projects
now use a different entry point for running tests, typically `pytest`
or `nosetests`.
Since the wheel format was introduced more tools were built to generate these,
e.g. `flit`. Since PEP 517 is provisionally accepted, defining a build-system
independent format (`pyproject.toml`), `pip` can now use that format to
execute the correct build-system.
In the past I've added support for PEP 517 (`pyproject`) to the Python
builder, resulting in a now rather large builder. Furthermore, it was not possible
to reuse components elsewhere. Therefore, the builder is now split into multiple
setup hooks.
The `setuptoolsCheckHook` is included now by default but in time it should
be removed from `buildPythonPackage` to make it easier to use another hook
(curently one has to pass in `dontUseSetuptoolsCheck`).
Thiago Kenji Okada