PackageLoader gives misleading error when wrong path given

[Dreamsorcerer]

Just spent 10 minutes trying to debug this error:

ValueError: The 'my_app' package was not installed in a way that PackageLoader understands.

The package is absolutely fine. I just set the path to a non-existing path, so this code was never run:
https://github.com/pallets/jinja/blob/main/src/jinja2/loaders.py#L318-L320

Maybe add an else to the for which raises a different error?

Or that piece of code could be simplified down to something like:

try:
    template_root = next(p for root in roots if os.path.isdir(p := os.path.join(root, package_path)))
except StopIteration:
    raise ValueError(f"Template path not found in package: {package_path}.")

Or if you convert everything to Path, that can be simplified to next(p for root in roots if (p := root / package_path).is_dir()).

[davidism]

Duplicate of #1705

[Dreamsorcerer]

Ah, thanks, missed that one.

For a PR, would the else be the desired change, or would the suggested refactor be good (I note that it does use the controversial walrus operator)?

[davidism]

There's already an open PR linked to that issue.

[Dreamsorcerer]

OK, I think it's wrong though. Will leave some feedback.