## Summary
If you have a file `typing.py` in the current working directory, `python
-m` doesn't work in some Python versions:
```sh
❯ python -m foo
Could not import runpy module
Traceback (most recent call last):
File "/Users/crmarsh/.local/share/rtx/installs/python/3.9.18/lib/python3.9/runpy.py", line 15, in <module>
import importlib.util
File "/Users/crmarsh/.local/share/rtx/installs/python/3.9.18/lib/python3.9/importlib/util.py", line 2, in <module>
from . import abc
File "/Users/crmarsh/.local/share/rtx/installs/python/3.9.18/lib/python3.9/importlib/abc.py", line 17, in <module>
from typing import Protocol, runtime_checkable
ImportError: cannot import name 'Protocol' from 'typing' (/Users/crmarsh/workspace/uv/typing.py)
```
This did _not_ cause problems for us on Python 3.11 or later, because we
set `PYTHONSAFEPATH`, which avoids adding the current working directory
to `sys.path`. However, on earlier versions, we _were_ failing with the
above. (It's important that we run interpreter discovery in the current
working directory, since doing otherwise breaks pyenv shims.)
The fix implemented here uses `-I` to run Python in isolated mode, which
is even stricter. The downside of isolated mode is that we currently
rely on setting `PYTHONPATH` to find the "fake module" that we create on
disk, and `-I` means `PYTHONPATH` is totally ignored. So, instead, we
run a script directly, and that _script_ injects the path we care about
into `PYTHONSAFEPATH`.
Closes https://github.com/astral-sh/uv/issues/2547.
The architecture of uv does not necessarily match that of the python
interpreter (#2326). In cross compiling/testing scenarios the operating
system can also mismatch. To solve this, we move arch and os detection
to python, vendoring the relevant pypa/packaging code, preventing
mismatches between what the python interpreter was compiled for and what
uv was compiled for.
To make the scripts more manageable, they are now a directory in a
tempdir and we run them with `python -m` . I've simplified the
pypa/packaging code since we're still building the tags in rust. A
`Platform` is now instantiated by querying the python interpreter for
its platform. The pypa/packaging files are copied verbatim for easier
updates except a `lru_cache()` python 3.7 backport.
Error handling is done by a `"result": "success|error"` field that allow
passing error details to rust:
```console
$ uv venv --no-cache
× Can't use Python at `/home/konsti/projects/uv/.venv/bin/python3`
╰─▶ Unknown operation system `linux`
```
I've used the [maturin sysconfig
collection](855f6d2cb1/sysconfig)
as reference. I'm unsure how to test these changes across the wide
variety of platforms.
Fixes#2326
