BLIP: enable generation tests

[zucchini-nlp]

What does this PR do?

Enables generation tests for BLIP models, except BLIP-1 (turned out to be a bit harder). I changed the generation tests to use modelTest.input_name as BLIP is the only model that uses pixel values as main input and thus checking generated text length's will always fail.

I tried to get rid of custom generate for these models, but that opened a Pandora box so I think better not waste time on an old model and maintain it for a while, until the model gets deprecated. But still I did some changes so we don't need to add extra bos at the beginning and now the decoder-based BLIP models return full text at output. Encoder-decoder based models return only generated text, which is consistent with what an LLM should do

[HuggingFaceDocBuilderDev]

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[gante]

changed the generation tests to use modelTest.input_name as BLIP is the only model that uses pixel values as main input and thus checking generated text length's will always fail.

I'd like very much to avoid this change -- extra logic for all tests to handle a niche corner case. Let's brainstorm alternatives! main_input in the generative tests is used to check the shapes. Perhaps we always want to look for input_ids or inputs_embeds in the input dictionary? 🤔

[zucchini-nlp]

@gante I tried to force input_ids always and I found another corner case with Whisper which expects input_features to be the main input for shape checking. I would very much love to make BLIP standard and maybe I'll make so in v5, because it will break a whole lot of things.

OMG, I found an option while writing this reply, whisper and the other audio model are encoder-decoder so we can make it work by getting main input in decoder-only models. Just before the check happens, in the same indent block :)
If you agree, I'll make the change hehe

[ArthurZucker]

AH actually we might need / want to force return_dict to TRUE, to avoid all the if elses

[gante]

OMG, I found an option while writing this reply, whisper and the other audio model are encoder-decoder so we can make it work by getting main input in decoder-only models. Just before the check happens, in the same indent block :)
If you agree, I'll make the change hehe

if it works, sounds good! (make sure to leave a comment)

[zucchini-nlp]

@gante requesting re-review, since the input-name was merged as a separate PR. I rebased main and ran tests again