🚨 out_indices always a list

[amyeroberts]

What does this PR do?

Recent updates to timm changed the type of the attribute model.feature_info.out_indices. Previously, out_indices would reflect the input type of out_indices on the create_model call i.e. either tuple or list. Now, this value is always a tuple. This causes the following failure on main:

FAILED tests/models/timm_backbone/test_modeling_timm_backbone.py::TimmBackboneModelTest::test_timm_transformer_backbone_equivalence - AssertionError: (1, 2, 3) != [1, 2, 3]

Example CI run: https://app.circleci.com/pipelines/github/huggingface/transformers/93542/workflows/38bfe697-908c-4d2c-a05c-7b99090fb084/jobs/1226834

As list are more useful and consistent for us -- we cannot save tuples in configs, they must be converted to lists first -- we instead choose to cast out_indices to always be a list.

This has the possibility of being a slight breaking change if users are creating models and relying on out_indices on being a tuple. As this property only happens when a new model is created, and not if it's saved and reloaded (because of the config), then I think this has a low chance of having much of an impact.

The following tests were run to make sure everything is still OK:

pytest tests/utils/test_backbone_utils.py
pytest tests/models/timm_backbone/test_modeling_timm_backbone.py
pytest tests/models/swin/test_modeling_swin.py::SwinBackboneTest

[HuggingFaceDocBuilderDev]

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[ydshieh]

Sound good to me but with a nit question. Would like to hear from @NielsRogge too.

Thanks!

[ArthurZucker]

If we need them to be mutable, cool to cast to list!

[amyeroberts]

If we need them to be mutable, cool to cast to list!

@ArthurZucker It's not that we need them to be mutable (in fact, we probably don't), it's to do with consistent typing when saving / loading configs. Previously, we just followed the out_indices from timm, which could be tuples or lists. However, for our models, because they're loaded through the configs, if a model is saved out with out_indices which are a tuple, it'll be cast to a list because of writing as a json. Previously, timm would respect whichever type was used to create the model, but now only uses tuples. This PR enforces a casting to list to make sure:

• We're consistent across backbones: timm vs. transformers
• timm models have out_indices consistently set to lists across timm versions