## Summary
macOS 11 has been EOL for 7 months, and it seems like it's common to
publish ARM-only wheels at 12.0+. I think this is a better default for
ARM macs.
Closes https://github.com/astral-sh/uv/issues/3227.
## Test Plan
`cargo run pip install scikit-learn==1.3.2 --python-platform macos
--no-build`
Adds hidden `--preview` / `--no-preview` flags with `UV_PREVIEW`
environment variable support. Copies the `PreviewMode` type from Ruff.
Does a little bit of extra work to port `uv run` to the new settings
model.
Note we allow `uv run` invocations without preview and only use its
presence to toggle an experimental warning.
## Test plan
```
❯ cargo run -q -- run --no-workspace -- python --version
warning: `uv run` is experimental and may change without warning.
Python 3.12.2
❯ cargo run -q -- run --no-workspace --preview -- python --version
Python 3.12.2
❯ UV_PREVIEW=1 cargo run -q -- run --no-workspace -- python --version
Python 3.12.2
```
## Summary
This PR adds basic struct definitions along with a "workspace" concept
for discovering settings. (The "workspace" terminology is used to match
Ruff; I did not invent it.)
A few notes:
- We discover any `pyproject.toml` or `uv.toml` file in any parent
directory of the current working directory. (We could adjust this to
look at the directories of the input files.)
- We don't actually do anything with the configuration yet; but those
PRs are large and I want this to be reviewed in isolation.
When running the `uv-client` tests, i would previously get:
```
warning: field `0` is never read
--> crates/uv-configuration/src/config_settings.rs:43:27
|
43 | pub struct ConfigSettings(BTreeMap<String, ConfigSettingValue>);
| -------------- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
| |
| field in this struct
|
= note: `ConfigSettings` has derived impls for the traits `Clone` and `Debug`, but these are intentionally ignored during dead code analysis
= note: `#[warn(dead_code)]` on by default
help: consider changing the field to be of unit type to suppress this warning while preserving the field numbering, or remove the field
|
43 | pub struct ConfigSettings(());
| ~~
warning: `uv-configuration` (lib) generated 1 warning
```
Needed to prevent circular dependencies in my toolchain work (#2931). I
think this is probably a reasonable change as we move towards persistent
configuration too?
Unfortunately `BuildIsolation` needs to be in `uv-types` to avoid
circular dependencies still. We might be able to resolve that in the
future.
