PyTest's AssertionRewritingHook not recognised

[marty-se]

I tried modulegraph2 on a project that uses pytest, but ended up with:

RuntimeError: Don't known how to handle <_pytest.assertion.rewrite.AssertionRewritingHook object at 0x117370c50> for <module>

Obviously, there is no case for AssertionRewritingHook (nor importlib.abc.MetaPathFinder which it implements: https://github.com/pytest-dev/pytest/blob/master/src/_pytest/assertion/rewrite.py#L56) in node_for_spec(). I'm however not sure what the appropriate solution would be...?

Thanks.

[ronaldoussoren]

I need to look into this. I thought I had added support for all of importlib, but I clearly missed the MetaPathFinder case :-(

[ronaldoussoren]

How can I reproduce the issue?

I've tried the following script from the pytest documentation:

import pytest

def checkconfig(x):
    __tracebackhide__ = True
    if not hasattr(x, "config"):
        pytest.fail("not configured: {}".format(x))

def test_something():
    checkconfig(42)

That works fine though, even if I add other imports below the import of pytest.

[marty-se]

Hmm, right, I realise now that my issue is probably related to the fact that I use modulegraph2 from a pytest plugin.

I have a script that looks like this:

import re

import modulegraph2
import pytest

class MyPlugin:

    def __init__(self):
        self.collected = []
        self.modulegraph = modulegraph2.ModuleGraph()

    def pytest_collection_modifyitems(self, items):
        for item in items:
            nodeid = item.nodeid
            module_spec = self._module_spec_from_nodeid(nodeid)

            self.modulegraph.add_module(module_spec)

    def _module_spec_from_nodeid(self, nodeid: str) -> str:
        matches = re.match(r'(.*)\.py::.*', nodeid)
        assert matches
        filepath_part = matches[0]
        return filepath_part.replace('/', '.')

def main():
    my_plugin = MyPlugin()
    pytest.main(['--collect-only', 'tests/'], plugins=[my_plugin])

if __name__ == '__main__':
    main()

... and I also have a tests/test_foo.py file with the contents from your example. I can then reproduce the error by running my script.

I guess pytest installs the import hook while collecting tests...

[ronaldoussoren]

Thanks. Having a reproducer makes it easier to fix the issue.

[ronaldoussoren]

I can reproduce the issue, but fixing this cleanly is harder. The AssertionRewritingHook in the traceback does not implement the API that modulegraph2 uses to inspect the loading process.

[ronaldoussoren]

I've filed a feature request with PyTest: https://github.com/pytest-dev/pytest/issues/7804

The requests asks to implement the InspectLoader ABC, which would solve the issue without changes in modulegraph2.

[marty-se]

Thank you so much for looking into this. Fixing it on the pytest side sounds reasonable.

[ronaldoussoren]

The pytest project is open for the idea, but requires a pull request. I'm not sure when I'll get around to that.

I'm keeping this open to track the pytest feature request, and because I want to add a modulegraph2 test to ensure this keeps working after it is implemented.

[ronaldoussoren]

PR for the pytest changes: https://github.com/pytest-dev/pytest/pull/7885

That PR is currently incomplete, I've primarily created it to ask if the proposed code changes are acceptable. But with the PR the reproducer for this issue no longer fails (although I still need to create code to validate the structure of the generated graph).