feat: support None to remove envvars

nox/command.py

@@ -55,17 +55,15 @@ def which(program: str | os.PathLike[str], paths: Sequence[str] | None) -> str:
  raise CommandFailed(f"Program {program} not found")
 
 
-def _clean_env(env: Mapping[str, str] | None = None) -> dict[str, str] | None:
+def _clean_env(env: Mapping[str, str | None] | None = None) -> dict[str, str] | None:
  if env is None:
  return None
 
- clean_env: dict[str, str] = {}
+ clean_env = {k: v for k, v in env.items() if v is not None}
 
  # Ensure systemroot is passed down, otherwise Windows will explode.
  if sys.platform == "win32":
- clean_env["SYSTEMROOT"] = os.environ.get("SYSTEMROOT", "")
-
- clean_env.update(env)
+ clean_env.setdefault("SYSTEMROOT", os.environ.get("SYSTEMROOT", ""))
 
  return clean_env
 
@@ -77,7 +75,7 @@ def _shlex_join(args: Sequence[str | os.PathLike[str]]) -> str:
 def run(
  args: Sequence[str | os.PathLike[str]],
  *,
- env: Mapping[str, str] | None = None,
+ env: Mapping[str, str | None] | None = None,
  silent: bool = False,
  paths: Sequence[str] | None = None,
  success_codes: Iterable[int] | None = None,

nox/sessions.py

@@ -283,7 +283,7 @@ def _run_func(
  def run(
  self,
  *args: str | os.PathLike[str],
- env: Mapping[str, str] | None = None,
+ env: Mapping[str, str | None] | None = None,
  include_outer_env: bool = True,
  **kwargs: Any,
  ) -> Any | None:
@@ -350,7 +350,9 @@ def run(
  print("Current Git commit is", out.strip())
 
  :param env: A dictionary of environment variables to expose to the
- command. By default, all environment variables are passed.
+ command. By default, all environment variables are passed. You
+ can block an environment variable from the outer environment by
+ setting it to None.
  :type env: dict or None
  :param include_outer_env: Boolean parameter that determines if the
  environment variables from the nox invocation environment should
@@ -406,7 +408,7 @@ def run(
  def run_install(
  self,
  *args: str | os.PathLike[str],
- env: Mapping[str, str] | None = None,
+ env: Mapping[str, str | None] | None = None,
  include_outer_env: bool = True,
  **kwargs: Any,
  ) -> Any | None:
@@ -474,7 +476,7 @@ def run_install(
  def run_always(
  self,
  *args: str | os.PathLike[str],
- env: Mapping[str, str] | None = None,
+ env: Mapping[str, str | None] | None = None,
  include_outer_env: bool = True,
  **kwargs: Any,
  ) -> Any | None:
@@ -490,7 +492,7 @@ def run_always(
  def _run(
  self,
  *args: str | os.PathLike[str],
- env: Mapping[str, str] | None = None,
+ env: Mapping[str, str | None] | None = None,
  include_outer_env: bool = True,
  **kwargs: Any,
  ) -> Any:
@@ -501,10 +503,8 @@ def _run(
 
  # Combine the env argument with our virtualenv's env vars.
  if include_outer_env:
- overlay_env = env
- env = self.env.copy()
- if overlay_env is not None:
- env.update(overlay_env)
+ overlay_env = env or {}
+ env = {**self.env, **overlay_env}
 
  # If --error-on-external-run is specified, error on external programs.
  if self._runner.global_config.error_on_external_run:

nox/virtualenv.py

@@ -78,15 +78,13 @@ def __init__(
  self, bin_paths: None = None, env: Mapping[str, str | None] | None = None
  ) -> None:
  self._bin_paths = bin_paths
- self.env = os.environ.copy()
  self._reused = False
- env = env or {}
 
- for k, v in env.items():
-  if v is None:
-  self.env.pop(k, None)
-  else:
-  self.env[k] = v
+ # Filter envs now so `.env` is dict[str, str] (easier to use)
+ # even though .command's env supports None.
+ env = env or {}
+ env = {**os.environ, **env}
+ self.env = {k: v for k, v in env.items() if v is not None}
 
  for key in _BLACKLISTED_ENV_VARS:
  self.env.pop(key, None)

tests/test_command.py

@@ -144,6 +144,19 @@ def test_run_env_unicode():
  assert "123" in result
 
 
+def test_run_env_remove(monkeypatch):
+ monkeypatch.setenv("EMPTY", "notempty")
+ nox.command.run(
+ [PYTHON, "-c", 'import os; assert "EMPTY" in os.environ'],
+ silent=True,
+ )
+ nox.command.run(
+ [PYTHON, "-c", 'import os; assert "EMPTY" not in os.environ'],
+ silent=True,
+ env={"EMPTY": None},
+ )
+
+
 @mock.patch("sys.platform", "win32")
 def test_run_env_systemroot():
  systemroot = os.environ.setdefault("SYSTEMROOT", "sigil")

tests/test_sessions.py

@@ -271,14 +271,15 @@ def test_run_overly_env(self):
  session, runner = self.make_session_and_runner()
  runner.venv.env["A"] = "1"
  runner.venv.env["B"] = "2"
+ runner.venv.env["C"] = "4"
  result = session.run(
  sys.executable,
  "-c",
- 'import os; print(os.environ["A"], os.environ["B"])',
- env={"B": "3"},
+ 'import os; print(os.environ["A"], os.environ["B"], os.environ.get("C", "5"))',
+ env={"B": "3", "C": None},
  silent=True,
  )
- assert result.strip() == "1 3"
+ assert result.strip() == "1 3 5"
 
  def test_by_default_all_invocation_env_vars_are_passed(self):
  session, runner = self.make_session_and_runner()