For a path dep such as the root project, uv can read metadata statically
from `pyproject.toml` or dynamically from the build backend.
Python's `packaging`
[sorts](cc938f984b/src/packaging/specifiers.py (L777))
specifiers before emitting them, so all build backends built on top of
it - such as hatchling - will change the specifier order compared to
pyproject.toml. The core metadata spec does say "If a field is not
marked as Dynamic, then the value of the field in any wheel built from
the sdist MUST match the value in the sdist", but it doesn't specify if
"match" means string equivalent or semantically equivalent, so it's
arguable if that spec conformant. This change means that the specifiers
have a different ordering when coming from the build backend than when
read statically from pyproject.toml.
Previously, we tried to read path dep metadata in order:
* From the (built wheel) cache (`packaging` order)
* From pyproject.toml (verbatim specifier)
* From a fresh build (`packaging` order)
This behaviour is unstable: On the first run, we cache is cold, so we
read the verbatim specifier from `pyproject.toml`, then we build and
store the metadata in the cache. On the second run, we read the
`packaging` sorted specifier from the cache.
Reproducer:
```shell
rm -rf newproj
uv init -q --no-config newproj
cd newproj/
uv add -q "anyio>=4,<5"
cat uv.lock | grep "requires-dist"
uv sync -q
cat uv.lock | grep "requires-dist"
cd ..
```
```
requires-dist = [{ name = "anyio", specifier = ">=4,<5" }]
requires-dist = [{ name = "anyio", specifier = "<5,>=4" }]
```
A project either has static metadata, so we can read from
pyproject.toml, or it doesn't, and we always read from the build through
`packaging`. We can use this to stabilize the behavior by slightly
switching the order.
* From pyproject.toml (verbatim specifier)
* From the (built wheel) cache (`packaging` order)
* From a fresh build (`packaging` order)
Potentially, we still want to sort the specifiers we get anyway, after
all, the is no guarantee that the specifiers from a build backend are
deterministic. But our metadata reading behavior should be independent
of the cache state, hence changing the order in the PR.
Fixes#6316
cabca7bf23