chore(qwen2): display warning log only when sliding window attention …
Author: edwardzjl
Pull request: yes

…is enabled

# What does this PR do?

In #36162, [a tiny refactor](https://github.com/huggingface/transformers/commit/96f01a36ac60c57be279cb7f027eac7e37fa90e8#diff-9032c4741cb5215be5f63709a8c866fd57e39becd5d108ac3ae6a7d551712aa7) has been made to qwen2:

```diff
diff --git a/src/transformers/models/qwen2/configuration_qwen2.py b/src/transformers/models/qwen2/configuration_qwen2.py
index 16979865e4..2e82f1976f 100644
--- a/src/transformers/models/qwen2/configuration_qwen2.py
+++ b/src/transformers/models/qwen2/configuration_qwen2.py
@@ -174,7 +174,7 @@ class Qwen2Config(PretrainedConfig):
         self.num_hidden_layers = num_hidden_layers
         self.num_attention_heads = num_attention_heads
         self.use_sliding_window = use_sliding_window
-        self.sliding_window = sliding_window if use_sliding_window else None
+        self.sliding_window = sliding_window  # we check `use_sliding_window` in the modeling code
         self.max_window_layers = max_window_layers

         # for backward compatibility
```

However, during modeling, this `sliding_window` attribute will trigger a warning log, even if it is not enabled:

https://github.com/huggingface/transformers/blob/e18f233f6c8cba029324e2868fb68abdaf6badf3/src/transformers/models/qwen2/modeling_qwen2.py#L237-L241

This PR could prevent this warning message being displayed if sliding window is not enabled, which reduces unnecessary confusion.

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Comments:
@ArthurZucker Sorry to bother, but I'm not sure if I am doing it correctly.

According to the header:

https://github.com/huggingface/transformers/blob/e18f233f6c8cba029324e2868fb68abdaf6badf3/src/transformers/models/qwen2/modeling_qwen2.py#L1-L6

I should not edit the `modeling_qwen2.py` directly, so I made the changes to the `modular_qwen2.py`. However, it seems that the CI is failing because the `modeling_qwen2.py` is not consistent with `modular_qwen2.py`:

https://app.circleci.com/pipelines/github/huggingface/transformers/119338/workflows/c1ea9aee-f73c-463d-b1c2-514cb89d4b72/jobs/1612428?utm_campaign=vcs-integration-link&utm_medium=referral&utm_source=github-checks-link&utm_content=summary

I also encountered this. This PR can solve an incorrect warning.

```
Qwen2Config {
  "use_sliding_window": false,
}
Sliding Window Attention is enabled but not implemented for `sdpa`; unexpected results may be encountered.
```


Also stumbled on this: `Sliding Window Attention is enabled but not implemented for "sdpa"`

during running line: `python3 -c "import transformers; transformers.pipeline('text-generation', model='Qwen/Qwen2.5-0.5B-Instruct')"`

from https://verl.readthedocs.io/en/latest/start/quickstart.html#step-2-download-a-model-for-post-training

The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_36316). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.