Remove max length beam scorer
Author: GeetDsa
Pull request: yes

# What does this PR do?

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Fixes #11040
Modifies ad per the comments from Pull #11122 


## Before submitting
- [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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## Who can review?
@patil-suraj ; @patrickvonplaten ; @Narsil 


Note: I have modified code in the `./tests/` where, `max_length` was used with `beam_scorer`.
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Comments:
Awesome job @GeetDsa - this looks good to me :-) 

Also pinging @patil-suraj and @Narsil for review.

@Narsil - do you think we need a test here or should this be fine without?

Hi @patrickvonplaten , Most of the errors are caused because of "max_length" attribute used while creating `beam_scorer` object in the test cases. These errors are arising as the beam_scorer attribute is removed from the source code. Infact, I had modified the files under `tests/*` to take account for this.(This can be found in my commits. Sorry that I did not had different commits for the actual source code and the tests).  So, may be can you review the files that I have modified under `tests/*`  as well?

I think we shouldn´t modify the tests if possible (thats what make backward compatiblity enforced).

Instead, we should probably : 
- add some warning for users that used the raw components/functions
- point the towards a better solution
- modify the tests that DO raise warnings to make sure we do raise them (and also swallow them in the logs) (they become backward compatibility tests their names should probably reflect that too) (We can remove some backward tests if they are very redundant btw)
- Have new tests that point show new API.
- Higher level tests (within models) should not be affected.
@GeetDsa  I can do this for you if you want.

> I think we shouldn´t modify the tests if possible (thats what make backward compatiblity enforced).
> 
> Instead, we should probably :
> 
> * add some warning for users that used the raw components/functions
> * point the towards a better solution
> * modify the tests that DO raise warnings to make sure we do raise them (and also swallow them in the logs) (they become backward compatibility tests their names should probably reflect that too) (We can remove some backward tests if they are very redundant btw)
> * Have new tests that point show new API.
> * Higher level tests (within models) should not be affected.
>   @GeetDsa  I can do this for you if you want.

Hi @Narsil, I think it would be better if you can do it, as I don't really know how to deal with tests.

> > I think we shouldn´t modify the tests if possible (thats what make backward compatiblity enforced).
> > Instead, we should probably :
> > 
> > * add some warning for users that used the raw components/functions
> > * point the towards a better solution
> > * modify the tests that DO raise warnings to make sure we do raise them (and also swallow them in the logs) (they become backward compatibility tests their names should probably reflect that too) (We can remove some backward tests if they are very redundant btw)
> > * Have new tests that point show new API.
> > * Higher level tests (within models) should not be affected.
> >   @GeetDsa  I can do this for you if you want.


 Hi @Narsil, I think it would be better if you can do it, as I don't really know how to deal with tests.



I'll take care of it

@Narsil - I think we don't need to add a test here. By design the PR prevents errors such as the one mentioned in the issue - It's not possible anymore to pass `max_length` to `BeamSearchScorer` and thus a test doesn't make much sense here IMO.

Will wait for https://github.com/huggingface/transformers/pull/11442 to be merged before rebasing this one to merge

@patrickvonplaten But if users were using the BeamScorer object, that's a breaking change, isn't it ?

> @patrickvonplaten But if users were using the BeamScorer object, that's a breaking change, isn't it ?

Yes true. IMO, no functionality is lost though because:

- Previously, if one had passed `max_length` to both `def beam_search(...)` and `BeamSearchScorer(...)`, then there would have been a bug (see issue). The correct way of fixing the bug (while still allowing `BeamSearchScorer(...)` to accept `max_length`) would have been to overwrite `BeamSearchScorer's` max_length with `beam_search(...)`'s max_length. On the other hand it's never possible to **not** pass `max_length` to `def beam_search(...)` => therefore I think either way the `max_length` arg to `BeamSearchScorer` is useless (the `max_length` value of `beam_search(...)` would have been preferred in any way. 

=> However, we could/should probably add `**kwargs` to `BeamSearchScorer` that throws a warning if `max_length` is passed & says that's it's deprecated. This would be cleaner overall and have no breaking changes - what do you think @Narsil ?

Yep, that's what I had in mind, just accept it, raise a warning (and ignore it, exactly as it used to if I understand correctly) 

> Yep, that's what I had in mind, just accept it, raise a warning (and ignore it, exactly as it used to if I understand correctly)

Done! Could you review one last time and merge if ok for you? @Narsil 

@patrickvonplaten, thank you for taking care of it. I found a small issue in the warning message. The message provided in the latest commit is ""`max_length` should be passed directly to `beam_search(...)`, `beam_sample(...)`"", shouldn't you include "generate(..)" as well, as sometime, `generate(...)` inherently calls `beam_search(..,)` or `group_beam_search(..,)`, or other relevant functions.

> @patrickvonplaten, thank you for taking care of it. I found a small issue in the warning message. The message provided in the latest commit is ""`max_length` should be passed directly to `beam_search(...)`, `beam_sample(...)`"", shouldn't you include "generate(..)" as well, as sometime, `generate(...)` inherently calls `beam_search(..,)` or `group_beam_search(..,)`, or other relevant functions.

Hey @GeetDsa, 

It should be fine, since the warning is impossible to be triggered by `generate(...)` since when one calls `generate(...)`, one cannot pass `max_length` to `BeamScorer`