fix legacy tox --devenv venv

docs/changelog/2925.bugfix.rst

@@ -0,0 +1 @@
+Fix ``tox --devenv venv`` invocation without ``-e`` - by :user:`asottile`.

src/tox/session/cmd/legacy.py

@@ -105,6 +105,7 @@ def legacy(state: State) -> int:
         return list_env(state)
     if option.devenv_path:
         option.devenv_path = Path(option.devenv_path)
+        option.env = option.env or CliEnv("py")
         return devenv(state)
     if option.parallel != 0:  # only 0 means sequential
         return run_parallel(state)

src/tox/session/env_select.py

@@ -125,7 +125,6 @@ def __init__(self, state: State) -> None:
         self.on_empty_fallback_py = True
         self._warned_about: set[str] = set()  #: shared set of skipped environments that were already warned about
         self._state = state
-        self._cli_envs: CliEnv | None = getattr(self._state.conf.options, "env", None)
         self._defined_envs_: None | dict[str, _ToxEnvInfo] = None
         self._pkg_env_counter: Counter[str] = Counter()
         from tox.plugin.manager import MANAGER
@@ -139,6 +138,10 @@ def __init__(self, state: State) -> None:
         tox_env_filter_regex = getattr(state.conf.options, "skip_env", "").strip()
         self._filter_re = re.compile(tox_env_filter_regex) if tox_env_filter_regex else None
 
+    @property
+    def _cli_envs(self) -> CliEnv | None:
+        return getattr(self._state.conf.options, "env", None)
+
     def _collect_names(self) -> Iterator[tuple[Iterable[str], bool]]:
         """:return: sources of tox environments defined with name and if is marked as target to run"""
         if self._provision is not None:  # pragma: no branch

tests/session/cmd/test_legacy.py

@@ -78,13 +78,22 @@ def test_legacy_list_all(tox_project: ToxProjectCreator, mocker: MockerFixture,
     assert outcome.state.conf.options.show_core is False
 
 
-def test_legacy_devenv(tox_project: ToxProjectCreator, mocker: MockerFixture, tmp_path: Path) -> None:
+@pytest.mark.parametrize("args", [(), ("-e", "py")])
+def test_legacy_devenv(
+    tox_project: ToxProjectCreator,
+    mocker: MockerFixture,
+    tmp_path: Path,
+    args: tuple[str, ...],
+) -> None:
     devenv = mocker.patch("tox.session.cmd.legacy.devenv")
     into = tmp_path / "b"
 
-    outcome = tox_project({"tox.ini": ""}).run("le", "--devenv", str(into), "-e", "py")
+    outcome = tox_project({"tox.ini": ""}).run("le", "--devenv", str(into), *args)
+
+    outcome.state.envs.ensure_only_run_env_is_active()
 
     assert devenv.call_count == 1
+    assert set(outcome.state.conf.options.env) == {"py"}
     assert outcome.state.conf.options.devenv_path == into
 
 

tests/session/test_env_select.py

@@ -2,7 +2,10 @@
 
 import pytest
 
+from tox.config.cli.parse import get_options
 from tox.pytest import MonkeyPatch, ToxProjectCreator
+from tox.session.env_select import CliEnv, EnvSelector
+from tox.session.state import State
 
 
 def test_label_core_can_define(tox_project: ToxProjectCreator) -> None:
@@ -117,3 +120,11 @@ def test_tox_skip_env_logs(tox_project: ToxProjectCreator, monkeypatch: MonkeyPa
     outcome = project.run("l", "--no-desc")
     outcome.assert_success()
     outcome.assert_out_err("ROOT: skip environment mypy, matches filter 'm[y]py'\npy310\npy39\n", "")
+
+
+def test_env_select_lazily_looks_at_envs() -> None:
+    state = State(get_options(), [])
+    env_selector = EnvSelector(state)
+    # late-assigning env should be reflected in env_selector
+    state.conf.options.env = CliEnv("py")
+    assert set(env_selector.iter()) == {"py"}