fix(utils): try_to_load_from_cache now correctly handles refs/pr revisions

[OlivierDehaene]

When trying to load a file from cache with a revision of type refs/pr/<pr-number>, try_to_load_from_cache fails because the revision file is serialized to: HUGGINGFACE_HUB_CACHE/models--<object-id>/refs/refs/pr/<pr-number> which is not found by the current implementation using os.path.listdir since it only lists files at the current level.

This PR simply reads the file directly if it exists.

Maybe this should also mean that revision should use replace("/", "--") during download.

[HuggingFaceDocBuilderDev]

The documentation is not available anymore as the PR was closed or merged.

[Wauplin]

Thanks for reporting the issue and proposing a fix @OlivierDehaene!
Would you mind adding a test similar to this one please ? 🙏
Something like that: (not tested myself)

    def test_try_to_load_from_cache_specific_pr_revision_exists(self):
        HfApi().create_pull_request(DUMMY_MODEL_ID)
        filepath = hf_hub_download(DUMMY_MODEL_ID, filename=CONFIG_NAME, revision="refs/pr/1")
        attempt = try_to_load_from_cache(DUMMY_MODEL_ID, filename=CONFIG_NAME, revision="refs/pr/1")
        self.assertEqual(filepath, attempt)

[Wauplin]

Merci ! I'll merge it as soon as the CI is green :)

[julien-c]

(and yes i guess we hadn't planned for revision to be allowed to contain /... cc @LysandreJik , i guess we should replace it indeed?)