Fix legacy devenv

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/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"}