Switched build backend to flit

[agronholm]

This allows wheel to use isolated builds and not run into a circular dependency (since setuptools requires this project as a dependency for building wheels). As a bonus, we can consolidate all build and tooling configuration into pyproject.toml.

[codecov]

Codecov Report

Merging #436 (23e47ba) into main (ab82cea) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #436   +/-   ##
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  Coverage   67.57%   67.57%           
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  Files          12       12           
  Lines         916      916           
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  Hits          619      619           
  Misses        297      297           

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[agronholm]

It seems there is no way to have flit add a setup.py file using the PEP 517 build process. Is this correct?

[agronholm]

pypa/flit#501

[agronholm]

Now that I have ditched flit-scm for flit_core, is this now good to go?

[layday]

I'll just note that redistributors would have to install flit in addition to flit_core to be able to build a wheel sdist with setup.py if they are to be able to continue installing setuptools + wheel without the aid of PEP 517, and flit depends on several other packages which makes it unsuitable for bootstrapping¹. Therefore, redistributors who have been installing wheel from a git checkout (e.g. https://github.com/archlinux/svntogit-community/blob/a594d718f44efc8efa027eb4f7a5d214056bfab0/trunk/PKGBUILD#L19, https://github.com/NixOS/nixpkgs/blob/fec8555fb0598f7a177e88fe69061264e5786155/pkgs/development/python-modules/wheel/default.nix#L13) will need to switch to PyPI.

Something to watch out for is that flit has different package data inclusion criteria for packages built with flit build and the PEP 517 hooks.

Footnotes

1. packaging and build both still use setuptools, so setuptools will continue to be a bootstrapping requirement. ↩

[agronholm]

I am slowly being driven crazy by all these constraints. As for downstream packagers, the only consistent way to get their attention is by breaking something, and that is never a pleasant situation. That said, we do need to move to standardized packaging and I fear that many downstream packagers won't bother to do the migration work until they absolutely must.

Still, I think it would be prudent to open a discussion at discuss.python.org to collect feedback about the planned build configuration changes.

[layday]

I am slowly being driven crazy by all these constraints.

Not just you 😛

[henryiii]

FYI, the bootstrapping story should be much better now: pypa/build#394 (comment)

(Though build is not converted yet, I'll try to get to that soonish)

[jameshilliard]

Though build is not converted yet

Also packaging which is in the dependency tree of build needs to be converted as well.

[henryiii]

FYI, Anthony and co. actively fight others adding pyproject.toml support as well, see csachs/pyproject-flake8#13. Currently broken with Flake8 5 though might be fixable for now.

[henryiii]

FYI, Packaging and Build have both moved to Flit. Noticed the circular dependency issue in the last release, which Flit would solve.

[jameshilliard]

Packaging and Build have both moved to Flit.

Yeah, packaging still needs a new release with flit support from what I can tell however(I see build got one a few days ago).

[henryiii]

Build's 0.9.0 release was right before the Flit transition. We are thinking about doing one soon-ish with the new system, but I'm not sure there's a rush until there's a packaging release.

[jameshilliard]

Build's 0.9.0 release was right before the Flit transition.

Ah, yeah, just noticed that.

[vishwin]

Both build and packaging have released with flit as build backend.