Using pip to install host packages with pyproject.toml-based (PEP 517)
builds is problematic:
* If build isolation is used, pip will create an isolated build
environment, install any build dependencies for the requested package,
then build the requested package.
It does not appear currently possible to have pip install the build
dependencies with hash-checking mode enabled[1].
* If build isolation is not used, any build dependencies must be
installed in the build environment before invoking pip to build the
requested package[2].
This would require creating a package dependency resolution system to
install build dependencies, and any dependencies of dependencies, in
the correct order.
* It is very difficult to patch the packages installed by pip.
This adds a new include file (python3-host-build.mk) with recipes to
install host Python packages with pyproject.toml-based builds. This is
backwards-compatible with packages that require running setup.py.
Besides addressing the above issues (the OpenWrt build system already
resolves dependencies between packages, checks all source downloads
against known hashes, and supports patching packages), host packages
also:
* Capture package licensing and maintainer information
* Enable uscan checking for package updates/CVEs
* Are a known concept for OpenWrt packagers/developers
The existing functionality of using host pip to install packages will
remain for now, but should be considered deprecated and expected to be
removed in the future.
This also updates Py3Build/CheckHostPipVersionMatch for the case where
the host-pip-requirements directory does not exist or is empty.
[1]: https://pip.pypa.io/en/stable/user_guide/#changes-to-the-pip-dependency-resolver-in-20-3-2020
[2]: https://pip.pypa.io/en/stable/cli/pip_install/#cmdoption-no-build-isolation
Signed-off-by: Jeffery To <jeffery.to@gmail.com>
Jeffery To