Fix Windows path separators breaking relative imports of Hub custom-generate modules

[dltsum]

What

When a Hub repo's custom_generate/generate.py relative-imports a sibling module (e.g. beam_search.py in transformers-community/group-beam-search and constrained-beam-search), get_cached_module_file recurses to fetch it and builds the child path like this:

f"{Path(module_file).parent / module_needed}.py"

On Windows, Path("custom_generate/generate.py").parent / "beam_search" renders as custom_generate\beam_search, and that backslash path is then looked up on the Hub, where file names always use forward slashes:

OSError: transformers-community/group-beam-search does not appear to have a file named
custom_generate\beam_search.py. Checkout
'https://huggingface.co/transformers-community/group-beam-search/tree/main' for available files.

So custom_generate strategies whose code spans several files cannot be loaded at all on Windows. (Sibling repos whose generate.py is self-contained, like dola and contrastive-search, are unaffected — this only triggers on relative imports.)

Fix

Normalize the Hub-relative path with as_posix() before the recursive lookup. Local filesystem uses of the same value are unaffected (Windows accepts forward slashes), and on POSIX systems the rendered path is unchanged.

Verification

Windows 11, Python 3.14:

• GenerationIntegrationTests::test_hub_gen_strategies_2_transformers_community_group_beam_search and ..._3_transformers_community_constrained_beam_search: fail without the fix with the OSError above; pass with it.
• tests/utils/test_dynamic_module_utils.py: 16 passed.

🤖 Generated with Claude Code

[github-actions]

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