Ignore missing interpreters when classifying env type

We now separate environments into either run or packaging environments
[1]. As noted in 'tox.session.env_select.EnvSelector._defined_envs' [2],
the name of the environment is not enough to determine what type of
environment it is and we must actually build the environment and inspect
it. This allows us to prevent users *running* these packaging
environments (e.g. 'tox -e .pkg'). Part of this process of building an
environment is validating the base python. If this validation fails
(i.e. the Python version does not exist), we will raise
'tox.tox_env.python.api.NoInterpreter'. We were not handling this
exception, and thus the process of determining the types of each
environment would cause a failure if any environment requested a Python
version we did not support, even if we weren't actually trying to run
this environment.

The fix for this is simple: handle the exception and simply ignore these
unsupported environments.

While we're here, fix some issues with an existing test that were
noticed while adding new tests.

[1] https://tox.wiki/en/latest/upgrading.html#packaging-configuration-and-inheritance
[2] https://github.com/tox-dev/tox/blob/af35384bb2ee/src/tox/session/env_select.py#L173

Signed-off-by: Stephen Finucane <stephen@that.guru>
Closes: tox-dev#2811

docs/changelog/2811.bugfix.rst

@@ -0,0 +1,2 @@
+The combination of ``usedevelop = true`` and ``--skip-missing-interpreters=false`` will no longer fail for environments
+that were *not* invoked.

src/tox/tox_env/python/package.py

@@ -14,7 +14,7 @@
 from ..errors import Skip
 from ..package import Package, PackageToxEnv, PathPackage
 from ..runner import RunToxEnv
-from .api import Python
+from .api import NoInterpreter, Python
 from .pip.req_file import PythonDeps
 
 if TYPE_CHECKING:
@@ -87,7 +87,11 @@ def default_wheel_tag(conf: Config, env_name: str | None) -> str:  # noqa: U100
             # python only code are often compatible at major level (unless universal wheel in which case both 2/3)
             # c-extension codes are trickier, but as of today both poetry/setuptools uses pypa/wheels logic
             # https://github.com/pypa/wheel/blob/master/src/wheel/bdist_wheel.py#L234-L280
-            run_py = cast(Python, run_env).base_python
+            try:
+                run_py = cast(Python, run_env).base_python
+            except NoInterpreter:
+                run_py = None
+
             if run_py is None:
                 base = ",".join(run_env.conf["base_python"])
                 raise Skip(f"could not resolve base python with {base}")

tests/tox_env/python/test_python_runner.py

@@ -128,8 +128,39 @@ def test_extras_are_normalized(
     ("config", "cli", "expected"),
     [("false", "true", True), ("true", "false", False), ("false", "config", False), ("true", "config", True)],
 )
-def test_config_skip_missing_interpreters(tox_project: ToxProjectCreator, config: str, cli: str, expected: str) -> None:
+def test_config_skip_missing_interpreters(
+    tox_project: ToxProjectCreator,
+    config: str,
+    cli: str,
+    expected: bool,
+) -> None:
     py_ver = ".".join(str(i) for i in sys.version_info[0:2])
     project = tox_project({"tox.ini": f"[tox]\nenvlist=py4,py{py_ver}\nskip_missing_interpreters={config}"})
-    result = project.run("--skip-missing-interpreters", cli)
-    assert result.code == 0 if expected else 1
+    result = project.run(f"--skip-missing-interpreters={cli}")
+    assert result.code == (0 if expected else -1)
+
+
+@pytest.mark.parametrize(
+    ("skip", "env", "retcode"),
+    [
+        ("true", f"py{''.join(str(i) for i in sys.version_info[0:2])}", 0),
+        ("false", f"py{''.join(str(i) for i in sys.version_info[0:2])}", 0),
+        ("true", "py31", 0),
+        ("false", "py31", 1),
+        ("true", None, 0),
+        ("false", None, -1),
+    ],
+)
+def test_skip_missing_interpreters_specified_env(
+    tox_project: ToxProjectCreator,
+    skip: str,
+    env: str | None,
+    retcode: int,
+) -> None:
+    py_ver = "".join(str(i) for i in sys.version_info[0:2])
+    project = tox_project({"tox.ini": f"[tox]\nenvlist=py31,py{py_ver}\n[testenv]\nusedevelop=true"})
+    args = [f"--skip-missing-interpreters={skip}"]
+    if env:
+        args += ["-e", env]
+    result = project.run(*args)
+    assert result.code == retcode

whitelist.txt

@@ -142,6 +142,7 @@ replacer
 repo
 reqs
 retann
+retcode
 rfind
 rpartition
 rreq