T5 migration to new masking interface
Author: Aravind-11
Pull request: yes

# What does this PR do?

This PR migrates the T5 model to use the new masking utilities (`masking_utils.py`) for attention mask creation.  

Fixes # (40743)


## Before submitting
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      Pull Request section?
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      to it if that's the case.
- [ ] Did you make sure to update the documentation with your changes? Here are the
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      [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/main/docs#writing-source-documentation).
- [ ] Did you write any new necessary tests?


## Who can review?

 @vasqu @Rocketknight1 

Passed all existing test cases except for test_small_integration_test which needs GPU. I need guidance on additional test cases to be added for this. Thank you. 

Comments:
> `create_bidirectional_mask` is not correctly used atm + let's remove unnecessary comments (including the old ones that already exist, e.g. on the cross attn mask)
> 
> I expect that some other models depend on T5, can you check with `make fix-copies`?

Thank you for your review @vasqu . I Changed the parameters of create_bidirectional_mask.  I ran make fix-copies and there was one dependent model mT5 that updated automatically.

The corresponding functions in modeling_mt5.py now reflect the new create_causal_mask / create_bidirectional_mask usage.

run-slow: mt5, t5

This comment contains run-slow, running the specified jobs: 

models: ['models/mt5', 'models/t5']
quantizations: [] ...

run-slow: mt5, t5

This comment contains run-slow, running the specified jobs: 

models: ['models/mt5', 'models/t5']
quantizations: [] ...

@Aravind-11 this is a bit more complicated than anticipated, you can see the failing tests here https://github.com/huggingface/transformers/actions/runs/18776158789/job/53571258876

This means that torch export is failing. Also we would need to remove traces of the `_update_causal...` function

run-slow: mt5, t5

Not sure why executorch is failing with the new API tbh, reverted these parts. If you find anything that fixes this, then go ahead! I would wait a bit for you, but if the current state is ok with you, I would merge this.

cc @Cyrilvallez if you have time to check why exchanging the causal mask fails here for executorch

This comment contains run-slow, running the specified jobs: 

models: ['models/mt5', 'models/t5']
quantizations: [] ...

> Not sure why executorch is failing with the new API tbh, reverted these parts. If you find anything that fixes this, then go ahead! I would wait a bit for you, but if the current state is ok with you, I would merge this.
> 
> cc @Cyrilvallez if you have time to check why exchanging the causal mask fails here for executorch

Thanks @vasqu! I agree, it makes sense to merge this as-is for now. The main T5 migration seems to work well and I think Executorch can be debugged later. Appreciate the review and all the follow-up commits 🙏.

Checking some stuff with masking in #41852. Maybe I can fix the issue here as well then 

> Checking some stuff with masking in #41852. Maybe I can fix the issue here as well then

The changes made in that pr should be reflected here too? 

> Not sure why executorch is failing with the new API tbh, reverted these parts.

I meant these, working on a masking version that requires less special treatment for executorch

> > Not sure why executorch is failing with the new API tbh, reverted these parts.
> 
> I meant these, working on a masking version that requires less special treatment for executorch

Got it.

> > > Not sure why executorch is failing with the new API tbh, reverted these parts.
> > 
> > 
> > I meant these, working on a masking version that requires less special treatment for executorch
> 
> Got it.

Do you want me to migrate those changes here as well? 

No not yet at least

I checked that #41852 works with t5 and all new masks API. Let's wait for that PR and then change it here to use the new mask API for causal masks as well

> I checked that #41852 works with t5 and all new masks API. Let's wait for that PR and then change it here to use the new mask API for causal masks as well

Got it. Thank you.

> I checked that #41852 works with t5 and all new masks API. Let's wait for that PR and then change it here to use the new mask API for causal masks as well

I think that #28818 issue also can be solved after the #41852 is approved ? 

run-slow: mt5, t5

This comment contains `run-slow`, running the specified jobs: 

models: ["models/mt5", "models/t5"]
quantizations: []

## CI Results
[Workflow Run ⚙️](https://github.com/huggingface/transformers/actions/runs/19238919830)

✅ No failing test specific to this PR 🎉 !


**[For maintainers]** Suggested jobs to run (before merge)

run-slow: mt5, t5

> I pushed the new changes for causal, thx a lot for your patience @Aravind-11
> 
> @Cyrilvallez I'd merge this tomorrow or so except you have found anything critical

Awesome!!

The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_41804). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

Thx for sticking through this PR! Super neat to have this

> Thx for sticking through this PR! Super neat to have this

Thank you for the code review!!