[In progress] Add warning padding attention mask
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Fixes #16136 


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cc @gante <|||||>Thank you for the comment!

Based on my understanding, [this line of code](https://github.com/huggingface/transformers/pull/21916/files#diff-6b72b98c4c2dcfc6cc606843917733f5d858374fbc22a735ff483bbc0c1e63eaR1054) enables the checking process only once during the forward pass, so it should not significantly impact performance.

The current warning method only issue warnings when `attention_mask` is necessary (due to the presence of padding tokens in the input), but no `attention_mask` is provided. In other cases where `attention_mask` is not required, no warning is issued. The additional checking on special tokens allows a more detailed warning message. 

I agree that your suggested method is more concise and efficient, but it may generate warnings when `attention_mask` is not needed. 

Since it's my first time contributing to the community, I don't have a strong opinion towards either solution. The original work is by @ydshieh and @patrickvonplaten. Perhaps they have additional insights and can suggest a more effective solution.<|||||>> Why not a simple logger.warning_once()

This is recently introduced :-)<|||||>@anruijian It checks `input_ids` until there is a batch in which a `pad_token_id` exists. If a user is working on a problem where  they have no `pad_token_id` on their data and they don't pass the `attention_mask`, there is a check made every forward pass. I'd strongly advocate for a simple warning when the `attention_mask` is not passed 🤗 

As a side note, we have related problems at other points in the code base. Getting into the habit of passing the `attention_mask` would really make everyone happier!<|||||>@gante Just to confirm before updating the PR, we are going to remove `warn_if_pad_token_in_input_ids_no_attention_mask` method and use `logger.warning_once` in `forward()`:
```python
def forward(...):
    ...
    if not attention_mask:
        logger.warning_once(
            "\nWe strongly recommend passing an `attention_mask` to avoid possibly incorrectly computing the"
            " attention weights. "
        )
    ...
```<|||||>@anruijian correct :) I would add a short example in the warning, such as `(e.g. to correctly mask the pad tokens)`, but I'll leave that up to you!<|||||>@gante 
```python
def forward(...):
    ...
    if not attention_mask:
        logger.warning_once(
            "\nWe strongly recommend passing an `attention_mask` to avoid possibly incorrectly computing the"
            " attention weights. Example to correctly mask the pad tokens: model(input_ids, attention_mask=attention_mask)."
            " See https://huggingface.co/docs/transformers/v4.23.1/en/troubleshooting#incorrect-output-when-padding-tokens-arent-masked for more details."
        )
    ...
```
Does this example look good to you? I also link the official doc on the issue. Not sure if it's too long. Let me know what you think about this. Thanks!
<|||||>@anruijian sounds good to me! (A minor nit: the link is for v4.23 of the docs, should be `https://huggingface.co/docs/transformers/troubleshooting#incorrect-output-when-padding-tokens-arent-masked` instead)<|||||>This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

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