skip_missing_interpreters ignored with uv=0.8.0

[ziima]

Issue

With the release of uv=0.8.0 tox-uv returns errors in combination of skip_missing_interpreters = true and uv_python_preference = only-system. The same tox configuration works with plain tox and a tox with tox-uv and uv=0.7.2 installed.

Environment

Provide at least:

• OS: Debian

Output of pip list of the host Python, where tox is installed

Package       Version
------------- -------
cachetools    6.1.0
chardet       5.2.0
colorama      0.4.6
distlib       0.4.0
filelock      3.18.0
packaging     25.0
pip           25.1.1
platformdirs  4.3.8
pluggy        1.6.0
pyproject-api 1.9.1
tox           4.28.0
tox-uv        1.26.1
uv            0.8.0
virtualenv    20.32.0

Output of running tox

Output of tox -rvv

py39: 107 W remove tox env folder /tmp/pokus/.tox/py39 [tox/tox_env/api.py:357]
py39: 109 W venv> /home/vzima/.local/pipx/venvs/tox/bin/uv venv -p cpython3.9 --allow-existing -v --python-preference only-system /tmp/pokus/.tox/py39 [tox/tox_env/api.py:459]
DEBUG uv 0.8.0
DEBUG Using Python request `cpython@3.9` from explicit request
DEBUG Searching for CPython 3.9 in search path
DEBUG Found `cpython-3.13.5-linux-x86_64-gnu` at `/usr/bin/python3` (first executable in the search path)
DEBUG Skipping interpreter at `/usr/bin/python3` from first executable in the search path: does not satisfy request `3.9`
error: No interpreter found for CPython 3.9 in search path

hint: A managed Python download is available for CPython 3.9, but the Python preference is set to 'only system'
py39: 126 C exit 2 (0.02 seconds) /tmp/pokus> /home/vzima/.local/pipx/venvs/tox/bin/uv venv -p cpython3.9 --allow-existing -v --python-preference only-system /tmp/pokus/.tox/py39 pid=2435415 [tox/execute/api.py:294]
py39: FAIL ✖ in 0.02 seconds
py310: 127 W remove tox env folder /tmp/pokus/.tox/py310 [tox/tox_env/api.py:357]
py310: 128 W venv> /home/vzima/.local/pipx/venvs/tox/bin/uv venv -p cpython3.10 --allow-existing -v --python-preference only-system /tmp/pokus/.tox/py310 [tox/tox_env/api.py:459]
DEBUG uv 0.8.0
DEBUG Using Python request `cpython@3.10` from explicit request
DEBUG Searching for CPython 3.10 in search path
DEBUG Found `cpython-3.13.5-linux-x86_64-gnu` at `/usr/bin/python3` (first executable in the search path)
DEBUG Skipping interpreter at `/usr/bin/python3` from first executable in the search path: does not satisfy request `3.10`
error: No interpreter found for CPython 3.10 in search path

hint: A managed Python download is available for CPython 3.10, but the Python preference is set to 'only system'
py310: 152 C exit 2 (0.02 seconds) /tmp/pokus> /home/vzima/.local/pipx/venvs/tox/bin/uv venv -p cpython3.10 --allow-existing -v --python-preference only-system /tmp/pokus/.tox/py310 pid=2435426 [tox/execute/api.py:294]
py310: FAIL ✖ in 0.03 seconds
py311: 153 W remove tox env folder /tmp/pokus/.tox/py311 [tox/tox_env/api.py:357]
py311: 155 W venv> /home/vzima/.local/pipx/venvs/tox/bin/uv venv -p cpython3.11 --allow-existing -v --python-preference only-system /tmp/pokus/.tox/py311 [tox/tox_env/api.py:459]
DEBUG uv 0.8.0
DEBUG Using Python request `cpython@3.11` from explicit request
DEBUG Searching for CPython 3.11 in search path
DEBUG Found `cpython-3.13.5-linux-x86_64-gnu` at `/usr/bin/python3` (first executable in the search path)
DEBUG Skipping interpreter at `/usr/bin/python3` from first executable in the search path: does not satisfy request `3.11`
error: No interpreter found for CPython 3.11 in search path

hint: A managed Python download is available for CPython 3.11, but the Python preference is set to 'only system'
py311: 185 C exit 2 (0.03 seconds) /tmp/pokus> /home/vzima/.local/pipx/venvs/tox/bin/uv venv -p cpython3.11 --allow-existing -v --python-preference only-system /tmp/pokus/.tox/py311 pid=2435438 [tox/execute/api.py:294]
py312: 185 W remove tox env folder /tmp/pokus/.tox/py312 [tox/tox_env/api.py:357]
py311: FAIL ✖ in 0.03 seconds
py312: 189 W venv> /home/vzima/.local/pipx/venvs/tox/bin/uv venv -p cpython3.12 --allow-existing -v --python-preference only-system /tmp/pokus/.tox/py312 [tox/tox_env/api.py:459]
DEBUG uv 0.8.0
DEBUG Using Python request `cpython@3.12` from explicit request
DEBUG Searching for CPython 3.12 in search path
DEBUG Found `cpython-3.12.10-linux-x86_64-gnu` at `/usr/bin/python3.12` (first executable in the search path)
Using CPython 3.12.10 interpreter at: /usr/bin/python3.12
Creating virtual environment at: .tox/py312
DEBUG Using base executable for virtual environment: /usr/bin/python3.12
DEBUG Allowing existing directory due to `--allow-existing`
py312: 206 I exit 0 (0.02 seconds) /tmp/pokus> /home/vzima/.local/pipx/venvs/tox/bin/uv venv -p cpython3.12 --allow-existing -v --python-preference only-system /tmp/pokus/.tox/py312 pid=2435450 [tox/execute/api.py:294]
py312: 208 W commands[0]> python -c 'print("Test")' [tox/tox_env/api.py:459]
Test
py312: 231 I exit 0 (0.02 seconds) /tmp/pokus> python -c 'print("Test")' pid=2435459 [tox/execute/api.py:294]
py312: OK ✔ in 0.05 seconds
py313: 231 W remove tox env folder /tmp/pokus/.tox/py313 [tox/tox_env/api.py:357]
py313: 234 W venv> /home/vzima/.local/pipx/venvs/tox/bin/uv venv -p /home/vzima/.local/pipx/venvs/tox/bin/python --allow-existing -v --python-preference only-system /tmp/pokus/.tox/py313 [tox/tox_env/api.py:459]
DEBUG uv 0.8.0
DEBUG Using Python request `/home/vzima/.local/pipx/venvs/tox/bin/python` from explicit request
DEBUG Checking for Python interpreter at path `/home/vzima/.local/pipx/venvs/tox/bin/python`
Using CPython 3.13.5 interpreter at: /home/vzima/.local/pipx/venvs/tox/bin/python
Creating virtual environment at: .tox/py313
DEBUG Using base executable for virtual environment: /usr/bin/python3.13
DEBUG Allowing existing directory due to `--allow-existing`
py313: 250 I exit 0 (0.02 seconds) /tmp/pokus> /home/vzima/.local/pipx/venvs/tox/bin/uv venv -p /home/vzima/.local/pipx/venvs/tox/bin/python --allow-existing -v --python-preference only-system /tmp/pokus/.tox/py313 pid=2435465 [tox/execute/api.py:294]
py313: 252 W commands[0]> python -c 'print("Test")' [tox/tox_env/api.py:459]
Test
py313: 275 I exit 0 (0.02 seconds) /tmp/pokus> python -c 'print("Test")' pid=2435473 [tox/execute/api.py:294]
  py39: FAIL code 2 (0.02 seconds)
  py310: FAIL code 2 (0.03 seconds)
  py311: FAIL code 2 (0.03 seconds)
  py312: OK (0.05=setup[0.02]+cmd[0.02] seconds)
  py313: OK (0.04=setup[0.02]+cmd[0.02] seconds)
  evaluation failed :( (0.20 seconds)

Minimal example

Minimal tox.ini to reproduce the issue, assuming only some of the python versions are available in system:

[tox]
envlist =
    py39
    py310
    py311
    py312
    py313
skip_missing_interpreters = true

[testenv]
commands =
    python -c 'print("Test")'
uv_python_preference = only-system

[ziima]

uv venv returns exit code 2 in 0.8.0 instead of 1 in 0.7.2.

[musicinmybrain]

In #223, src/tox_uv/_venv.py is changed to supports both uv==0.8.0 and uv<0.8.0, but test_uv_venv_skip_missing_interpreters_fail now fails with uv<0.8.0. Was that intentional?

[ziima]

No, but I expect test_uv_venv_skip_missing_interpreters_fail would be run with the latest uv.