The loose consensus is that "fetch" doesn't have much meaning and that a
boolean flag makes more sense from the command line.
1. Adds `--allow-python-downloads` (hidden, default) and
`--no-python-downloads` to the CLI to quickly enable or disable
downloads
2. Deprecates `--python-fetch` in favor of the options from (1)
3. Removes `python-fetch` in favor of a `python-downloads` setting
5. Adds a `never` variant to the enum, allowing even explicit installs
to be disabled via the configuration file
## Test plan
I tested this with various `pyproject.toml`-level settings and `uv venv
--preview --python 3.12.2` and `uv python install 3.12.2` with and
without the new CLI flags.
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## Summary
Currently, `uv` refuses to install anything on GraalPy. This is
currently blocking GraalPy testing with cibuildwheel, since manylinux
includes both `uv` and `graalpy` (but doesn't test with `uv`), whereas
cibuildwheel defaults to `uv`. See e.g.
2750618295
where it gives
```
+ python -m build /project/sample_proj --wheel --outdir=/tmp/cibuildwheel/built_wheel --installer=uv
* Creating isolated environment: venv+uv...
* Using external uv from /usr/local/bin/uv
* Installing packages in isolated environment:
- setuptools >= 40.8.0
> /usr/local/bin/uv pip install "setuptools >= 40.8.0"
< error: Unknown implementation: `graalpy`
```
## Test Plan
I simply based the GraalPy support on PyPy and added some small tests.
I'm open to discussing how to test this. GraalPy is available for
manylinux images and with setup-python, so we should be able to add
tests against it to the CI. I locally confirmed by installing `uv` into
a GraalPy venv and then trying things like `uv pip install Pillow` and
testing those extensions.
Search for all `python3.x` minor versions in PATH, skipping those we
already know we can use.
For example, let's say `python` and `python3` are Python 3.10. When a
user requests `>= 3.11`, we still need to find a `python3.12` in PATH.
We do so with a regex matcher.
Fixes#4709
Whew this is a lot.
The user-facing changes are:
- `uv toolchain` to `uv python` e.g. `uv python find`, `uv python
install`, ...
- `UV_TOOLCHAIN_DIR` to` UV_PYTHON_INSTALL_DIR`
- `<UV_STATE_DIR>/toolchains` to `<UV_STATE_DIR>/python` (with
[automatic
migration](https://github.com/astral-sh/uv/pull/4735/files#r1663029330))
- User-facing messages no longer refer to toolchains, instead using
"Python", "Python versions" or "Python installations"
The internal changes are:
- `uv-toolchain` crate to `uv-python`
- `Toolchain` no longer referenced in type names
- Dropped unused `SystemPython` type (previously replaced)
- Clarified the type names for "managed Python installations"
- (more little things)
