The basic idea here is to make it so forking can only ever result in a
resolution that, for a particular marker environment, will only install
at most one version of a package. We can guarantee this by ensuring we
only fork on conflicting dependency specifications only when their
corresponding markers are completely disjoint. If they aren't, then
resolution _must_ find a single version of the package in the
intersection of the two dependency specifications.
A test for this case has been added to packse here:
https://github.com/astral-sh/packse/pull/182. Previously, that test
would result in a resolution with two different unconditional versions
of the same package. With this change, resolution fails (as it should).
A commit-by-commit review should be helpful here, since the first commit
is a refactor to make the second commit a bit more digestible.
## Summary
This PR attempts to use a similar trick to that we added in
https://github.com/astral-sh/uv/pull/1878, but for post-releases.
In https://github.com/astral-sh/uv/pull/1878, we added a fake "minimum"
version to enable us to treat `< 1.0.0` as _excluding_ pre-releases of
1.0.0.
Today, on `main`, we accept post-releases and local versions in `>
1.0.0`. But per PEP 440, that should _exclude_ post-releases and local
versions, unless the specifier is itself a pre-release, in which case,
pre-releases are allowed (e.g., `> 1.0.0.post0` should allow `>
1.0.0.post1`).
To support this, we add a fake "maximum" version that's greater than all
the post and local releases for a given version. This leverages our last
remaining free bit in the compact representation.
- Now that `packse` is being published to PyPI we can install it from
there.
- Tweaks the tooling around scenario updates to manage a temporary
virtual environment for you.
- Makes use of a new index URL
- Includes local version segment scenarios (supersedes
https://github.com/astral-sh/uv/pull/2022)
