Plan for flit-core v4

[Maxwell G]

Hi everyone,

A new major version of flit and flit-core was recently released [1].
Flit documentation previously recommended that packages pin flit-core to
`<4` in pyproject.toml metadata, which many projects did. There are 152
packages in rawhide that BuildRequire 'python3dist(flit-core)'. About
80% of those pin '<4'.

Note that, according to the flit changelog,
> This version contains breaking changes, but most projects which are

already using the [project] table for metadata shouldn’t be affected,
and can simply change the flit_core <4 constraint to <5.

so for many packages, the required changes would just be changing one
character ("4" to "5") in pyproject.toml (or patching the dependencies
using the %pyproject_patch_dependency macro as described below), but for
other packages that use `[tool.flit.metadata]`, the required changes
would be more involved.

How should we handle this? A couple potential options:

1. Mass add `%pyproject_patch_dependency flit-core:drop_upper` to all
affected packages where possible. This is the most quick-n-dirty
solution, but it doesn't contribute anything back to upstream projects.
This solution also wouldn't work for packages that need to be ported
away from `[tool.flit.metadata]`. We would need to figure out how many
tool.flit.metadata users there still are and handle them separately.
2. Start an effort to patch package dependency constraints in
pyproject.toml to allow both v3 and v4 and port [tool.flit.metadata]
usage where applicable. Send the patches to upstreams. Then, upgrade
python-flit-core to v4.
3. Update python-flit-core to v4 first, add a deprecated() v3 compat
package, and then slowly on patching flit-core users and eventually
removing the compat package.

Any thoughts about these ideas or other things that I missed? It would
be nice to get this figured out before F46 branching so we don't get
stuck with an old flit in EL 11.

All the best,
Maxwell

[1] https://bugzilla.redhat.com/show_bug.cgi?id=2511191

[Miro Hrončok]

On 13. 08. 26 22:14, Maxwell G wrote:
> Update python-flit-core to v4 first, add a deprecated() v3 compat
>
> package, and then slowly on patching flit-core users and eventually
> removing the compat package.

I think this is the safest plan. I can drive the adoption in ELN package set 
and co-maintain the compat package.

https://src.fedoraproject.org/rpms/python-flit-core/pull-request/21

[Miro Hrončok]

On 19. 08. 26 23:56, Miro Hrončok wrote:
> On 13. 08. 26 22:14, Maxwell G wrote:
> > Update python-flit-core to v4 first, add a deprecated() v3 compat
> >
> > package, and then slowly on patching flit-core users and eventually
> > removing the compat package.
>
> I think this is the safest plan. I can drive the adoption in ELN package set 
> and co-maintain the compat package.
>
> https://src.fedoraproject.org/rpms/python-flit-core/pull-request/21

Heads up: flit-core has been updated to version 4.

There is a deprecated() compat package python3-flit-core3 for packages that 
still need version < 4.

Migrating everything to flit-core 4+ will eventually be necessary.

For many packages, this is as simple as unpinning an upper bound of a 
dependency specification:

%pyproject_patch_dependency flit_core:set_upper:5

See e.g. https://src.fedoraproject.org/rpms/python-installer/pull-request/6

Others might need more changes to pyproject.toml, see e.g.

https://github.com/pexpect/ptyprocess/pull/84 (upstream)
https://src.fedoraproject.org/rpms/python-ptyprocess/pull-request/4