Our test driver exposes a bunch of variables and functions, which
pyflakes doesn't recognise by default because it assumes that the test
script is executed standalone. In reality however the test driver script
is using exec() on the testScript.
Fortunately pyflakes has $PYFLAKES_BUILTINS, which are the attributes
that are globally available on all modules to be checked. Since we only
have one module, using this environment variable is fine as opposed to
my first approach to this, which tried to use the unstable internal API
of pyflakes.
The attributes are gathered by the main derivation of the test driver,
because we don't want to end up defining a new attribute in the test
driver module just to being confused why using it in a test will result
in an error.
Another way we could have gathered these attributes would be in
mkDriver, which is where the linting takes place. However, we do have a
different set of Python dependencies in scope and duplicating these will
again just cause confusion over having it at one location only.
Signed-off-by: aszlig <aszlig@nix.build>
Co-Authored-By: aszlig <aszlig@nix.build>
So far, we have used "black" for formatting the test code, which is
rather strict and opinionated and when used inline in Nix expressions it
creates all sorts of trouble.
One of the main annoyances is that when using strings coming from Nix
expressions (eg. store paths or option definitions from NixOS modules),
completely unrelated changes could cause tests to fail, since eg. black
wants lines to be broken.
Another downside of enforcing a certain kind of formatting is that it
makes the Nix expression code inconsistent because we're mixing two
spaces of indentation (common in nixpkgs) with four spaces of
indentation as defined in PEP-8. While this is perfectly fine for
standalone Python files, it really looks ugly and inconsistent IMO when
used within Nix strings.
What we actually want though is a linter that catches problems early on
before actually running the test, because this is *actually* helping in
development because running the actual VM test takes much longer.
This is the reason why I switched from black to pyflakes, because the
latter actually has useful checks, eg. usage of undefined variables,
invalid format arguments, duplicate arguments, shadowed loop vars and
more.
Signed-off-by: aszlig <aszlig@nix.build>
Closes: https://github.com/NixOS/nixpkgs/issues/72964
