Install fails when UV sources are a list

[mdekstrand]

Issue

When entries in tools.uv.sources are lists instead of dictionaries, as is common in forked dependency structures such as multi-backend PyTorch setups, tox fails to install the virtual environment.

Example pyproject.toml snippet:

[tool.uv.sources]
torch = [
  { index = "pytorch-cpu", group = "cpu" },
  { index = "pytorch-gpu", group = "gpu" },
]

Stack trace:

Traceback (most recent call last):
  File "/Users/mde48/.local/share/uv/tools/tox/lib/python3.12/site-packages/tox/session/cmd/run/single.py", line 47, in _evaluate
    tox_env.setup()
  File "/Users/mde48/.local/share/uv/tools/tox/lib/python3.12/site-packages/tox/tox_env/api.py", line 285, in setup
    self._setup_with_env()
  File "/Users/mde48/.local/share/uv/tools/tox/lib/python3.12/site-packages/tox/tox_env/runner.py", line 146, in _setup_with_env
    self._setup_pkg()
  File "/Users/mde48/.local/share/uv/tools/tox/lib/python3.12/site-packages/tox/tox_env/runner.py", line 171, in _setup_pkg
    self._install(self._packages, RunToxEnv.__name__, "package")
  File "/Users/mde48/.local/share/uv/tools/tox/lib/python3.12/site-packages/tox/tox_env/api.py", line 119, in _install
    self.installer.install(arguments, section, of_type)
  File "/Users/mde48/.local/share/uv/tools/tox/lib/python3.12/site-packages/tox_uv/_installer.py", line 105, in install
    self._install_list_of_deps(arguments, section, of_type)
  File "/Users/mde48/.local/share/uv/tools/tox/lib/python3.12/site-packages/tox_uv/_installer.py", line 137, in _install_list_of_deps
    and pkg.name in self._sourced_pkg_names
                    ^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/mde48/.local/share/uv/python/cpython-3.12.11-macos-aarch64-none/lib/python3.12/functools.py", line 998, in __get__
    val = self.func(instance)
          ^^^^^^^^^^^^^^^^^^^
  File "/Users/mde48/.local/share/uv/tools/tox/lib/python3.12/site-packages/tox_uv/_installer.py", line 119, in _sourced_pkg_names
    return {key for key, val in sources.items() if val.get("workspace", False)}
                                                   ^^^^^^^
AttributeError: 'list' object has no attribute 'get'

After reviewing this function, it appears this line is assuming that tool.uv.sources maps package names to objects, but it is allowed to map them to lists of objects.

Environment

Provide at least:

• OS: macOS

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

not sure how to get this when using recommended uv tool install setup.

[gaborbernat]

PR welcome.