feat: Allow Noxfile to specify nox.options.error_on_missing_interpret…

…ers (#725)

nox/_option_set.py

@@ -115,6 +115,7 @@ def default(self) -> bool | str | None | list[str]:
 
 def flag_pair_merge_func(
     enable_name: str,
+    enable_default: bool | Callable[[], bool],
     disable_name: str,
     command_args: Namespace,
     noxfile_args: Namespace,
@@ -155,6 +156,10 @@ def flag_pair_merge_func(
     noxfile_value = getattr(noxfile_args, enable_name)
     command_value = getattr(command_args, enable_name)
     disable_value = getattr(command_args, disable_name)
+    default_value = enable_default() if callable(enable_default) else enable_default
+    if default_value and disable_value is None and noxfile_value != default_value:
+        # Makes sure make_flag_pair with default=true can be overridden via noxfile
+        disable_value = True
 
     return (command_value or noxfile_value) and not disable_value
 
@@ -163,7 +168,7 @@ def make_flag_pair(
     name: str,
     enable_flags: tuple[str, str] | tuple[str],
     disable_flags: tuple[str, str] | tuple[str],
-    default: bool = False,
+    default: bool | Callable[[], bool] = False,
     **kwargs: Any,
 ) -> tuple[Option, Option]:
     """Returns two options - one to enable a behavior and another to disable it.
@@ -178,7 +183,7 @@ def make_flag_pair(
         name,
         *enable_flags,
         noxfile=True,
-        merge_func=functools.partial(flag_pair_merge_func, name, disable_name),
+        merge_func=functools.partial(flag_pair_merge_func, name, default, disable_name),
         default=default,
         **kwargs,
     )

nox/_options.py

@@ -459,7 +459,7 @@ def _session_completer(
         ("--no-error-on-missing-interpreters",),
         group=options.groups["execution"],
         help="Error instead of skipping sessions if an interpreter can not be located.",
-        default="CI" in os.environ,
+        default=lambda: "CI" in os.environ,
     ),
     *_option_set.make_flag_pair(
         "error_on_external_run",

tests/resources/noxfile_options.py

@@ -17,6 +17,7 @@
 import nox
 
 nox.options.reuse_existing_virtualenvs = True
+# nox.options.error_on_missing_interpreters = {error_on_missing_interpreters} # used by tests
 nox.options.sessions = ["test"]
 
 

tests/test_main.py

@@ -694,3 +694,56 @@ def test_main_reuse_existing_virtualenvs_no_install(monkeypatch):
             nox.__main__.main()
         config = execute.call_args[1]["global_config"]
     assert config.reuse_existing_virtualenvs and config.no_install
+
+
+@pytest.mark.parametrize(
+    ("should_set_ci_env_var", "noxfile_option_value", "expected_final_value"),
+    [
+        (True, None, True),
+        (True, True, True),
+        (True, False, False),
+        (False, None, False),
+        (False, True, True),
+        (False, False, False),
+    ],
+)
+def test_main_noxfile_options_with_ci_override(
+    monkeypatch,
+    tmp_path,
+    should_set_ci_env_var,
+    noxfile_option_value,
+    expected_final_value,
+):
+    monkeypatch.delenv("CI", raising=False)  # make sure we have a clean environment
+    if should_set_ci_env_var:
+        monkeypatch.setenv("CI", "True")
+    # Reload nox.options taking into consideration monkeypatch.{delenv|setenv}
+    monkeypatch.setattr(
+        nox._options, "noxfile_options", nox._options.options.noxfile_namespace()
+    )
+    monkeypatch.setattr(nox, "options", nox._options.noxfile_options)
+
+    noxfile_path = Path(RESOURCES) / "noxfile_options.py"
+    if noxfile_option_value is not None:
+        # Temp noxfile with error_on_missing_interpreters set
+        noxfile_text = noxfile_path.read_text()
+        noxfile_text = noxfile_text.replace("# nox", "nox")
+        noxfile_text = noxfile_text.format(
+            error_on_missing_interpreters=noxfile_option_value
+        )
+        noxfile_path = tmp_path / "noxfile.py"
+        noxfile_path.write_text(noxfile_text)
+
+    monkeypatch.setattr(
+        sys,
+        "argv",
+        ["nox", "-l", "--noxfile", str(noxfile_path)],
+    )
+
+    with mock.patch(
+        "nox.tasks.honor_list_request", return_value=0
+    ) as honor_list_request:
+        with mock.patch("sys.exit"):
+            nox.__main__.main()
+        config = honor_list_request.call_args[1]["global_config"]
+    assert config.error_on_missing_interpreters == expected_final_value