Commits on Aug 7, 2024

1. Stop installing setuptools and wheel …

   Currently the buildpack performs a system site-packages install of not
   only pip, but also setuptools and wheel. This has historically been
   necessary for pip to be able to build source distributions (sdists) for
   packages that don't ship with compatible wheels.
   
   However:
   - Thanks to PEP 518, packages can now (and many already do) specify an
     explicit build backend using `[build-system]` in their
     `pyproject.toml`. The dependencies specified in that config (such as
     setuptools and wheel) will be installed by pip into an isolated and
     ephemeral build environment as part of the source distribution build
     process. Such packages therefore don't need/use globally installed
     setuptools/wheel versions.
   - As of pip v22.1, pip will now default to the isolated build environment
     mode (along with a fallback legacy setuptools build backend), if the
     setuptools package isn't installed globally. This means that packages
     that haven't yet migrated to a PEP 518 `pyproject.toml` build backend
     config can still build even if setuptools isn't installed globally.
   
   There are a small number of rarely used packages in the wild that
   aren't compatible with build isolation mode, however, these typically
   require more build dependencies than just setuptools, which means they
   wouldn't have worked with this buildpack anyway.
   
   As such, it's no longer necessary for us to install setuptools and wheel
   globally. This matches the behaviour of the `venv` and `ensurepip` modules
   in Python 3.12+, where setuptools and wheel installation has also been
   removed. And it also matches the default behaviour of Poetry too, whose
   `install --sync` command removes any implicitly installed packages in the
   current environment (other than pip).
   
   See:
   https://peps.python.org/pep-0518/
   https://pip.pypa.io/en/stable/reference/build-system/
   https://pip.pypa.io/en/stable/reference/build-system/pyproject-toml/#build-isolation
   pypa/pip#10717
   python/cpython#101039
   pypa/get-pip#218
   astral-sh/uv#2252
   
   GUS-W-16437776.

   

   edmorley committed Aug 7, 2024
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