Issue 1:
🚀 Feature request

Add decoding inputs to generate

Motivation

When generating with encoder-decoder, one may want to insert context for the decoder.

I'm currently working on summarization given that I know some parts of the gt. But other ideas can come to mind.

Your contribution

@torch.no_grad()
def generate(
self,
input_ids: Optional[torch.LongTensor] = None,
max_length: Optional[int] = None,
min_length: Optional[int] = None,
do_sample: Optional[bool] = None,
early_stopping: Optional[bool] = None,
num_beams: Optional[int] = None,
temperature: Optional[float] = None,
top_k: Optional[int] = None,
top_p: Optional[float] = None,
repetition_penalty: Optional[float] = None,
bad_words_ids: Optional[Iterable[int]] = None,
bos_token_id: Optional[int] = None,
pad_token_id: Optional[int] = None,
eos_token_id: Optional[int] = None,
length_penalty: Optional[float] = None,
no_repeat_ngram_size: Optional[int] = None,
num_return_sequences: Optional[int] = None,
attention_mask: Optional[torch.LongTensor] = None,
decoder_start_token_id: Optional[int] = None,
decoder_input_ids: Optional[torch.LongTensor] = None,
decoder_attention_mask: Optional[torch.LongTensor] = None,
use_cache: Optional[bool] = None,
**model_specific_kwargs
) -> torch.LongTensor:

r""" Generates sequences for models with a LM head. The method currently supports greedy decoding, beam-search decoding, sampling with temperature, sampling with top-k or nucleus sampling.

Adapted in part from Facebook's XLM beam search code_.

.. _Facebook's XLM beam search code:
https://github.com/facebookresearch/XLM/blob/9e6f6814d17be4fe5b15f2e6c43eb2b2d76daeb4/src/model/transformer.py#L529

Parameters:

input_ids: (`optional`) `torch.LongTensor` of shape `(batch_size, sequence_length)`
The sequence used as a prompt for the generation. If `None` the method initializes
it as an empty `torch.LongTensor` of shape `(1,)`.

max_length: (`optional`) int
The max length of the sequence to be generated. Between `min_length` and infinity. Default to 20.

min_length: (`optional`) int
The min length of the sequence to be generated. Between 0 and infinity. Default to 0.

do_sample: (`optional`) bool
If set to `False` greedy decoding is used. Otherwise sampling is used. Defaults to `False` as defined in `configuration_utils.PretrainedConfig`.

early_stopping: (`optional`) bool
if set to `True` beam search is stopped when at least `num_beams` sentences finished per batch. Defaults to `False` as defined in `configuration_utils.PretrainedConfig`.

num_beams: (`optional`) int
Number of beams for beam search. Must be between 1 and infinity. 1 means no beam search. Default to 1.

temperature: (`optional`) float
The value used to module the next token probabilities. Must be strictly positive. Default to 1.0.

top_k: (`optional`) int
The number of highest probability vocabulary tokens to keep for top-k-filtering. Between 1 and infinity. Default to 50.

top_p: (`optional`) float
The cumulative probability of parameter highest probability vocabulary tokens to keep for nucleus sampling. Must be between 0 and 1. Default to 1.

repetition_penalty: (`optional`) float
The parameter for repetition penalty. Between 1.0 and infinity. 1.0 means no penalty. Default to 1.0.

pad_token_id: (`optional`) int
Padding token. Default to specicic model pad_token_id or None if it does not exist.

bos_token_id: (`optional`) int
BOS token. Defaults to `bos_token_id` as defined in the models config.

eos_token_id: (`optional`) int
EOS token. Defaults to `eos_token_id` as defined in the models config.

length_penalty: (`optional`) float
Exponential penalty to the length. Default to 1.

no_repeat_ngram_size: (`optional`) int
If set to int > 0, all ngrams of size `no_repeat_ngram_size` can only occur once.
bad_words_ids: (`optional`) list of lists of int
`bad_words_ids` contains tokens that are not allowed to be generated. In order to get the tokens of the words that should not appear in the generated text, use `tokenizer.encode(bad_word, add_prefix_space=True)`.

num_return_sequences: (`optional`) int
The number of independently computed returned sequences for each element in the batch. Default to 1.

attention_mask (`optional`) obj: `torch.LongTensor` of same shape as `input_ids`
Mask to avoid performing attention on padding token indices.
Mask values selected in ``[0, 1]``:
``1`` for tokens that are NOT MASKED, ``0`` for MASKED tokens.
Defaults to `None`.

`What are attention masks? <../glossary.html#attention-mask>`__

decoder_start_token_id=None: (`optional`) int
If an encoder-decoder model starts decoding with a different token than BOS.
Defaults to `None` and is changed to `BOS` later.

use_cache: (`optional`) bool
If `use_cache` is True, past key values are used to speed up decoding if applicable to model. Defaults to `True`.

model_specific_kwargs: (`optional`) dict
Additional model specific kwargs will be forwarded to the `forward` function of the model.

Return:

output: `torch.LongTensor` of shape `(batch_size * num_return_sequences, sequence_length)`
sequence_length is either equal to max_length or shorter if all batches finished early due to the `eos_token_id`

Examples::

tokenizer = AutoTokenizer.from_pretrained('distilgpt2') # Initialize tokenizer
model = AutoModelWithLMHead.from_pretrained('distilgpt2') # Download model and configuration from S3 and cache.
outputs = model.generate(max_length=40) # do greedy decoding
print('Generated: {}'.format(tokenizer.decode(outputs[0], skip_special_tokens=True)))

tokenizer = AutoTokenizer.from_pretrained('openai-gpt') # Initialize tokenizer
model = AutoModelWithLMHead.from_pretrained('openai-gpt') # Download model and configuration from S3 and cache.
input_context = 'The dog'
input_ids = tokenizer.encode(input_context, return_tensors='pt') # encode input context
outputs = model.generate(input_ids=input_ids, num_beams=5, num_return_sequences=3, temperature=1.5) # generate 3 independent sequences using beam search decoding (5 beams) with sampling from initial context 'The dog'
for i in range(3): # 3 output sequences were generated
print('Generated {}: {}'.format(i, tokenizer.decode(outputs[i], skip_special_tokens=True)))

tokenizer = AutoTokenizer.from_pretrained('distilgpt2') # Initialize tokenizer
model = AutoModelWithLMHead.from_pretrained('distilgpt2') # Download model and configuration from S3 and cache.
input_context = 'The dog'
input_ids = tokenizer.encode(input_context, return_tensors='pt') # encode input context
outputs = model.generate(input_ids=input_ids, max_length=40, temperature=0.7, num_return_sequences=3) # 3 generate sequences using by sampling
for i in range(3): # 3 output sequences were generated
print('Generated {}: {}'.format(i, tokenizer.decode(outputs[i], skip_special_tokens=True)))

tokenizer = AutoTokenizer.from_pretrained('ctrl') # Initialize tokenizer
model = AutoModelWithLMHead.from_pretrained('ctrl') # Download model and configuration from S3 and cache.
input_context = 'Legal My neighbor is' # "Legal" is one of the control codes for ctrl
input_ids = tokenizer.encode(input_context, return_tensors='pt') # encode input context
outputs = model.generate(input_ids=input_ids, max_length=50, temperature=0.7, repetition_penalty=1.2) # generate sequences
print('Generated: {}'.format(tokenizer.decode(outputs[0], skip_special_tokens=True)))

tokenizer = AutoTokenizer.from_pretrained('gpt2') # Initialize tokenizer
model = AutoModelWithLMHead.from_pretrained('gpt2') # Download model and configuration from S3 and cache.
input_context = 'My cute dog' # "Legal" is one of the control codes for ctrl
bad_words_ids = [tokenizer.encode(bad_word, add_prefix_space=True) for bad_word in ['idiot', 'stupid', 'shut up']]
input_ids = tokenizer.encode(input_context, return_tensors='pt') # encode input context
outputs = model.generate(input_ids=input_ids, max_length=100, do_sample=True, bad_words_ids=bad_words_ids) # generate sequences without allowing bad_words to be generated
"""

# We cannot generate if the model does not have a LM head
if self.get_output_embeddings() is None:
raise AttributeError(
"You tried to generate sequences with a model that does not have a LM Head."
"Please use another model class (e.g. `OpenAIGPTLMHeadModel`, `XLNetLMHeadModel`, `GPT2LMHeadModel`, `CTRLLMHeadModel`, `T5WithLMHeadModel`, `TransfoXLLMHeadModel`, `XLMWithLMHeadModel`, `BartForConditionalGeneration` )"
)

max_length = max_length if max_length is not None else self.config.max_length
min_length = min_length if min_length is not None else self.config.min_length
do_sample = do_sample if do_sample is not None else self.config.do_sample
early_stopping = early_stopping if early_stopping is not None else self.config.early_stopping
use_cache = use_cache if use_cache is not None else self.config.use_cache
num_beams = num_beams if num_beams is not None else self.config.num_beams
temperature = temperature if temperature is not None else self.config.temperature
top_k = top_k if top_k is not None else self.config.top_k
top_p = top_p if top_p is not None else self.config.top_p
repetition_penalty = repetition_penalty if repetition_penalty is not None else self.config.repetition_penalty
bos_token_id = bos_token_id if bos_token_id is not None else self.config.bos_token_id
pad_token_id = pad_token_id if pad_token_id is not None else self.config.pad_token_id
eos_token_id = eos_token_id if eos_token_id is not None else self.config.eos_token_id
length_penalty = length_penalty if length_penalty is not None else self.config.length_penalty
no_repeat_ngram_size = (
no_repeat_ngram_size if no_repeat_ngram_size is not None else self.config.no_repeat_ngram_size
)
bad_words_ids = bad_words_ids if bad_words_ids is not None else self.config.bad_words_ids
num_return_sequences = (
num_return_sequences if num_return_sequences is not None else self.config.num_return_sequences
)
decoder_start_token_id = (
decoder_start_token_id if decoder_start_token_id is not None else self.config.decoder_start_token_id
)

if input_ids is not None:
batch_size = input_ids.shape[0] # overriden by the input batch_size
else:
batch_size = 1

assert isinstance(max_length, int) and max_length > 0, "`max_length` should be a strictly positive integer."
assert isinstance(min_length, int) and min_length >= 0, "`min_length` should be a positive integer."
assert isinstance(do_sample, bool), "`do_sample` should be a boolean."
assert isinstance(early_stopping, bool), "`early_stopping` should be a boolean."
assert isinstance(use_cache, bool), "`use_cache` should be a boolean."
assert isinstance(num_beams, int) and num_beams > 0, "`num_beams` should be a strictly positive integer."
assert temperature > 0, "`temperature` should be strictly positive."
assert isinstance(top_k, int) and top_k >= 0, "`top_k` should be a positive integer."
assert 0 <= top_p <= 1, "`top_p` should be between 0 and 1."
assert repetition_penalty >= 1.0, "`repetition_penalty` should be >= 1."
assert input_ids is not None or (
isinstance(bos_token_id, int) and bos_token_id >= 0
), "If input_ids is not defined, `bos_token_id` should be a positive integer."
assert pad_token_id is None or (
isinstance(pad_token_id, int) and (pad_token_id >= 0)
), "`pad_token_id` should be a positive integer."
assert (eos_token_id is None) or (
isinstance(eos_token_id, int) and (eos_token_id >= 0)
), "`eos_token_id` should be a positive integer."
assert length_penalty > 0, "`length_penalty` should be strictly positive."
assert (
isinstance(no_repeat_ngram_size, int) and no_repeat_ngram_size >= 0
), "`no_repeat_ngram_size` should be a positive integer."
assert (
isinstance(num_return_sequences, int) and num_return_sequences > 0
), "`num_return_sequences` should be a strictly positive integer."
assert (
bad_words_ids is None or isinstance(bad_words_ids, list) and isinstance(bad_words_ids[0], list)
), "`bad_words_ids` is either `None` or a list of lists of tokens that should not be generated"

if input_ids is None:
assert isinstance(bos_token_id, int) and bos_token_id >= 0, (
"you should either supply a context to complete as `input_ids` input "
"or a `bos_token_id` (integer >= 0) as a first token to start the generation."
)
input_ids = torch.full(
(batch_size, 1), bos_token_id, dtype=torch.long, device=next(self.parameters()).device,
)
else:
assert input_ids.dim() == 2, "Input prompt should be of shape (batch_size, sequence length)."

# not allow to duplicate outputs when greedy decoding
if do_sample is False:
if num_beams == 1:
# no_beam_search greedy generation conditions
assert (
num_return_sequences == 1
), "Greedy decoding will always produce the same output for num_beams == 1 and num_return_sequences > 1. Please set num_return_sequences = 1"

else:
# beam_search greedy generation conditions
assert (
num_beams >= num_return_sequences
), "Greedy beam search decoding cannot return more sequences than it has beams. Please set num_beams >= num_return_sequences"

# create attention mask if necessary
# TODO (PVP): this should later be handled by the forward fn() in each model in the future see PR 3140
if (attention_mask is None) and (pad_token_id is not None) and (pad_token_id in input_ids):
attention_mask = input_ids.ne(pad_token_id).long()
elif attention_mask is None:
attention_mask = input_ids.new_ones(input_ids.shape)

# set pad_token_id to eos_token_id if not set. Important that this is done after
# attention_mask is created
if pad_token_id is None and eos_token_id is not None:
logger.warning(
"Setting `pad_token_id` to {} (first `eos_token_id`) to generate sequence".format(eos_token_id)
)
pad_token_id = eos_token_id

# current position and vocab size
if hasattr(self.config, "vocab_size"):
vocab_size = self.config.vocab_size
elif (
self.config.is_encoder_decoder
and hasattr(self.config, "decoder")
and hasattr(self.config.decoder, "vocab_size")
):
vocab_size = self.config.decoder.vocab_size

# set effective batch size and effective batch multiplier according to do_sample
if do_sample:
effective_batch_size = batch_size * num_return_sequences
effective_batch_mult = num_return_sequences
else:
effective_batch_size = batch_size
effective_batch_mult = 1

if self.config.is_encoder_decoder:
if decoder_start_token_id is None:
decoder_start_token_id = bos_token_id

assert (
decoder_start_token_id is not None
), "decoder_start_token_id or bos_token_id has to be defined for encoder-decoder generation"
assert hasattr(self, "get_encoder"), "{} should have a 'get_encoder' function defined".format(self)
assert callable(self.get_encoder), "{} should be a method".format(self.get_encoder)

# get encoder and store encoder outputs
encoder = self.get_encoder()

encoder_outputs: tuple = encoder(input_ids, attention_mask=attention_mask)

# Expand input ids if num_beams > 1 or num_return_sequences > 1

if self.config.is_encoder_decoder:
if decoder_input_ids is not None:
input_ids = decoder_input_ids
else:
# create empty decoder_input_ids
input_ids = torch.full(
(effective_batch_size * num_beams, 1),
decoder_start_token_id,
dtype=torch.long,
device=next(self.parameters()).device,
)
cur_len = 1

assert (
batch_size == encoder_outputs[0].shape[0]
), f"expected encoder_outputs[0] to have 1st dimension bs={batch_size}, got {encoder_outputs[0].shape[0]} "

# expand batch_idx to assign correct encoder output for expanded input_ids (due to num_beams > 1 and num_return_sequences > 1)
expanded_batch_idxs = (
torch.arange(batch_size)
.view(-1, 1)
.repeat(1, num_beams * effective_batch_mult)
.view(-1)
.to(input_ids.device)
)
# expand encoder_outputs
encoder_outputs = (encoder_outputs[0].index_select(0, expanded_batch_idxs), *encoder_outputs[1:])

else:
encoder_outputs = None
cur_len = input_ids.shape[-1]

assert (
cur_len < max_length
), f"The context has {cur_len} number of tokens, but `max_length` is only {max_length}. Please make sure that `max_length` is bigger than the number of tokens, by setting either `generate(max_length=...,...)` or `config.max_length = ...`"

if num_return_sequences > 1 or num_beams > 1:
input_ids_len = input_ids.shape[-1]
input_ids = input_ids.unsqueeze(1).expand(batch_size, effective_batch_mult * num_beams, input_ids_len)
attention_mask = attention_mask.unsqueeze(1).expand(
batch_size, effective_batch_mult * num_beams, attention_mask.shape[-1]
)

input_ids = input_ids.contiguous().view(
effective_batch_size * num_beams, input_ids_len
) # shape: (batch_size * num_return_sequences * num_beams, cur_len)
attention_mask = attention_mask.contiguous().view(
effective_batch_size * num_beams, attention_mask.shape[-1]
) # shape: (batch_size * num_return_sequences * num_beams, cur_len)

if num_beams > 1:
output = self._generate_beam_search(
input_ids,
cur_len=cur_len,
max_length=max_length,
min_length=min_length,
do_sample=do_sample,
early_stopping=early_stopping,
temperature=temperature,
top_k=top_k,
top_p=top_p,
repetition_penalty=repetition_penalty,
no_repeat_ngram_size=no_repeat_ngram_size,
bad_words_ids=bad_words_ids,
pad_token_id=pad_token_id,
eos_token_id=eos_token_id,
batch_size=effective_batch_size,
num_return_sequences=num_return_sequences,
length_penalty=length_penalty,
num_beams=num_beams,
vocab_size=vocab_size,
encoder_outputs=encoder_outputs,
attention_mask=attention_mask,
use_cache=use_cache,
decoder_attention_mask=decoder_attention_mask,
model_specific_kwargs=model_specific_kwargs,
)
else:
output = self._generate_no_beam_search(
input_ids,
cur_len=cur_len,
max_length=max_length,
min_length=min_length,
do_sample=do_sample,
temperature=temperature,
top_k=top_k,
top_p=top_p,
repetition_penalty=repetition_penalty,
no_repeat_ngram_size=no_repeat_ngram_size,
bad_words_ids=bad_words_ids,
pad_token_id=pad_token_id,
eos_token_id=eos_token_id,
batch_size=effective_batch_size,
encoder_outputs=encoder_outputs,
attention_mask=attention_mask,
use_cache=use_cache,
decoder_attention_mask=decoder_attention_mask,
model_specific_kwargs=model_specific_kwargs,
)

return output

def _generate_no_beam_search(
self,
input_ids,
cur_len,
max_length,
min_length,
do_sample,
temperature,
top_k,
top_p,
repetition_penalty,
no_repeat_ngram_size,
bad_words_ids,
pad_token_id,
eos_token_id,
batch_size,
encoder_outputs,
attention_mask,
use_cache,
decoder_attention_mask,
model_specific_kwargs,
):
""" Generate sequences for each example without beam search (num_beams == 1).
All returned sequence are generated independantly.
"""
# length of generated sentences / unfinished sentences
unfinished_sents = input_ids.new(batch_size).fill_(1)
sent_lengths = input_ids.new(batch_size).fill_(max_length)

past = (encoder_outputs, None) if encoder_outputs is not None else None
while cur_len < max_length:
model_inputs = self.prepare_inputs_for_generation(
input_ids, past=past, attention_mask=attention_mask, use_cache=use_cache, **model_specific_kwargs
)

model_inputs['decoder_attention_mask'] = decoder_attention_mask
outputs = self(**model_inputs)

next_token_logits = outputs[0][:, -1, :]

scores = self.postprocess_next_token_scores(
scores=next_token_logits,
input_ids=input_ids,
no_repeat_ngram_size=no_repeat_ngram_size,
bad_words_ids=bad_words_ids,
cur_len=cur_len,
min_length=min_length,
max_length=max_length,
eos_token_id=eos_token_id,
repetition_penalty=repetition_penalty,
batch_size=batch_size,
num_beams=1,
)

# if model has past, then set the past variable to speed up decoding
if self._use_cache(outputs, use_cache):
past = outputs[1]

if do_sample:
# Temperature (higher temperature => more likely to sample low probability tokens)
if temperature != 1.0:
scores = scores / temperature
# Top-p/top-k filtering
next_token_logscores = top_k_top_p_filtering(scores, top_k=top_k, top_p=top_p)
# Sample
probs = F.softmax(next_token_logscores, dim=-1)
next_token = torch.multinomial(probs, num_samples=1).squeeze(1)
else:
# Greedy decoding
next_token = torch.argmax(next_token_logits, dim=-1)

# update generations and finished sentences
if eos_token_id is not None:
# pad finished sentences if eos_token_id exist
tokens_to_add = next_token * unfinished_sents + (pad_token_id) * (1 - unfinished_sents)
else:
tokens_to_add = next_token

# add token and increase length by one
input_ids = torch.cat([input_ids, tokens_to_add.unsqueeze(-1)], dim=-1)
cur_len = cur_len + 1

if eos_token_id is not None:
eos_in_sents = tokens_to_add == eos_token_id
# if sentence is unfinished and the token to add is eos, sent_lengths is filled with current length
is_sents_unfinished_and_token_to_add_is_eos = unfinished_sents.mul(eos_in_sents.long()).bool()
sent_lengths.masked_fill_(is_sents_unfinished_and_token_to_add_is_eos, cur_len)
# unfinished_sents is set to zero if eos in sentence
unfinished_sents.mul_((~eos_in_sents).long())

# stop when there is a 
 in each sentence, or if we exceed the maximul length
if unfinished_sents.max() == 0:
break

# extend attention_mask for new generated input if only decoder
if self.config.is_encoder_decoder is False:
attention_mask = torch.cat(
[attention_mask, attention_mask.new_ones((attention_mask.shape[0], 1))], dim=-1
)

return input_ids

def _generate_beam_search(
self,
input_ids,
cur_len,
max_length,
min_length,
do_sample,
early_stopping,
temperature,
top_k,
top_p,
repetition_penalty,
no_repeat_ngram_size,
bad_words_ids,
pad_token_id,
eos_token_id,
batch_size,
num_return_sequences,
length_penalty,
num_beams,
vocab_size,
encoder_outputs,
attention_mask,
use_cache,
decoder_attention_mask,
model_specific_kwargs,
):
""" Generate sequences for each example with beam search.
"""

# generated hypotheses
generated_hyps = [
BeamHypotheses(num_beams, max_length, length_penalty, early_stopping=early_stopping)
for _ in range(batch_size)
]

# scores for each sentence in the beam
beam_scores = torch.zeros((batch_size, num_beams), dtype=torch.float, device=input_ids.device)

# for greedy decoding it is made sure that only tokens of the first beam are considered to avoid sampling the exact same tokens three times
if do_sample is False:
beam_scores[:, 1:] = -1e9
beam_scores = beam_scores.view(-1) # shape (batch_size * num_beams,)

# cache compute states
past = (encoder_outputs, None) if encoder_outputs is not None else None

# done sentences
done = [False for _ in range(batch_size)]

while cur_len < max_length:
model_inputs = self.prepare_inputs_for_generation(
input_ids, past=past, attention_mask=attention_mask, use_cache=use_cache, **model_specific_kwargs
)
model_inputs['decoder_attention_mask'] = decoder_attention_mask
outputs = self(**model_inputs) # (batch_size * num_beams, cur_len, vocab_size)
next_token_logits = outputs[0][:, -1, :] # (batch_size * num_beams, vocab_size)

# if model has past, then set the past variable to speed up decoding
if self._use_cache(outputs, use_cache):
past = outputs[1]
if self.config.is_encoder_decoder and do_sample is False:
# TODO (PVP) still a bit hacky here - there might be a better solution
next_token_logits = self.adjust_logits_during_generation(
next_token_logits, cur_len=cur_len, max_length=max_length
)

scores = F.log_softmax(next_token_logits, dim=-1) # (batch_size * num_beams, vocab_size)

scores = self.postprocess_next_token_scores(
scores=scores,
input_ids=input_ids,
no_repeat_ngram_size=no_repeat_ngram_size,
bad_words_ids=bad_words_ids,
cur_len=cur_len,
min_length=min_length,
max_length=max_length,
eos_token_id=eos_token_id,
repetition_penalty=repetition_penalty,
batch_size=batch_size,
num_beams=num_beams,
)

assert scores.shape == (batch_size * num_beams, vocab_size), "Shapes of scores: {} != {}".format(
scores.shape, (batch_size * num_beams, vocab_size)
)

if do_sample:
_scores = scores + beam_scores[:, None].expand_as(scores) # (batch_size * num_beams, vocab_size)
# Temperature
if temperature != 1.0:
_scores = _scores / temperature
# Top-p/top-k filtering
_scores = top_k_top_p_filtering(
_scores, top_k=top_k, top_p=top_p, min_tokens_to_keep=2
) # (batch_size * num_beams, vocab_size)
# re-organize to group the beam together to sample from all beam_idxs
_scores = _scores.contiguous().view(
batch_size, num_beams * vocab_size
) # (batch_size, num_beams * vocab_size)

# Sample 2 next tokens for each beam (so we have some spare tokens and match output of greedy beam search)
probs = F.softmax(_scores, dim=-1)
next_tokens = torch.multinomial(probs, num_samples=2 * num_beams) # (batch_size, num_beams * 2)
# Compute next scores
next_scores = torch.gather(_scores, -1, next_tokens) # (batch_size, num_beams * 2)
# sort the sampled vector to make sure that the first num_beams samples are the best
next_scores, next_scores_indices = torch.sort(next_scores, descending=True, dim=1)
next_tokens = torch.gather(next_tokens, -1, next_scores_indices) # (batch_size, num_beams * 2)

else:
next_scores = scores + beam_scores[:, None].expand_as(scores) # (batch_size * num_beams, vocab_size)

# re-organize to group the beam together (we are keeping top hypothesis accross beams)
next_scores = next_scores.view(
batch_size, num_beams * vocab_size
) # (batch_size, num_beams * vocab_size)

next_scores, next_tokens = torch.topk(next_scores, 2 * num_beams, dim=1, largest=True, sorted=True)

assert next_scores.size() == next_tokens.size() == (batch_size, 2 * num_beams)

# next batch beam content
next_batch_beam = []

# for each sentence
for batch_idx in range(batch_size):

# if we are done with this sentence, add a pad token
if done[batch_idx]:
assert (
len(generated_hyps[batch_idx]) >= num_beams
), "Batch can only be done if at least {} beams have been generated".format(num_beams)
assert (
eos_token_id is not None and pad_token_id is not None
), "generated beams >= num_beams -> eos_token_id and pad_token have to be defined"
next_batch_beam.extend([(0, pad_token_id, 0)] * num_beams) # pad the batch
continue

# next sentence beam content, this will get added to next_batch_beam
next_sent_beam = []

# next tokens for this sentence
for beam_token_rank, (beam_token_id, beam_token_score) in enumerate(
zip(next_tokens[batch_idx], next_scores[batch_idx])
):
# get beam and token IDs
beam_id = beam_token_id // vocab_size
token_id = beam_token_id % vocab_size

effective_beam_id = batch_idx * num_beams + beam_id
# add to generated hypotheses if end of sentence
if (eos_token_id is not None) and (token_id.item() == eos_token_id):
# if beam_token does not belong to top num_beams tokens, it should not be added
is_beam_token_worse_than_top_num_beams = beam_token_rank >= num_beams
if is_beam_token_worse_than_top_num_beams:
continue
generated_hyps[batch_idx].add(
input_ids[effective_beam_id].clone(), beam_token_score.item(),
)
else:
# add next predicted token since it is not eos_token
next_sent_beam.append((beam_token_score, token_id, effective_beam_id))

# once the beam for next step is full, don't add more tokens to it.
if len(next_sent_beam) == num_beams:
break

# Check if we are done so that we can save a pad step if all(done)
done[batch_idx] = done[batch_idx] or generated_hyps[batch_idx].is_done(
next_scores[batch_idx].max().item(), cur_len
)

# update next beam content
assert len(next_sent_beam) == num_beams, "Beam should always be full"
next_batch_beam.extend(next_sent_beam)
assert len(next_batch_beam) == num_beams * (batch_idx + 1), "We should have added num_beams each step"

# stop when we are done with each sentence
if all(done):
break

# sanity check / prepare next batch
assert len(next_batch_beam) == batch_size * num_beams
beam_scores = beam_scores.new([x[0] for x in next_batch_beam])
beam_tokens = input_ids.new([x[1] for x in next_batch_beam])
beam_idx = input_ids.new([x[2] for x in next_batch_beam])

# re-order batch and update current length
input_ids = input_ids[beam_idx, :]
input_ids = torch.cat([input_ids, beam_tokens.unsqueeze(1)], dim=-1)
cur_len = cur_len + 1

# re-order internal states
if past is not None:
past = self._reorder_cache(past, beam_idx)

# extend attention_mask for new generated input if only decoder
if self.config.is_encoder_decoder is False:
attention_mask = torch.cat(
[attention_mask, attention_mask.new_ones((attention_mask.shape[0], 1))], dim=-1
)

# finalize all open beam hypotheses and add to generated hypotheses
for batch_idx in range(batch_size):
if done[batch_idx]:
continue

# test that beam scores match previously calculated scores if not eos and batch_idx not done
if eos_token_id is not None and all(
(token_id % vocab_size).item() != eos_token_id for token_id in next_tokens[batch_idx]
):
assert torch.all(
next_scores[batch_idx, :num_beams] == beam_scores.view(batch_size, num_beams)[batch_idx]
), "If batch_idx is not done, final next scores: {} have to equal to accumulated beam_scores: {}".format(
next_scores[:, :num_beams][batch_idx], beam_scores.view(batch_size, num_beams)[batch_idx],
)

# need to add best num_beams hypotheses to generated hyps
for beam_id in range(num_beams):
effective_beam_id = batch_idx * num_beams + beam_id
final_score = beam_scores[effective_beam_id].item()
final_tokens = input_ids[effective_beam_id]
generated_hyps[batch_idx].add(final_tokens, final_score)

# depending on whether greedy generation is wanted or not define different output_batch_size and output_num_return_sequences_per_batch
output_batch_size = batch_size if do_sample else batch_size * num_return_sequences
output_num_return_sequences_per_batch = 1 if do_sample else num_return_sequences

# select the best hypotheses
sent_lengths = input_ids.new(output_batch_size)
best = []

# retrieve best hypotheses
for i, hypotheses in enumerate(generated_hyps):
sorted_hyps = sorted(hypotheses.beams, key=lambda x: x[0])
for j in range(output_num_return_sequences_per_batch):
effective_batch_idx = output_num_return_sequences_per_batch * i + j
best_hyp = sorted_hyps.pop()[1]
sent_lengths[effective_batch_idx] = len(best_hyp)
best.append(best_hyp)

# shorter batches are padded
if sent_lengths.min().item() != sent_lengths.max().item():
assert pad_token_id is not None, "`Pad_token_id` has to be defined"
sent_max_len = min(sent_lengths.max().item() + 1, max_length)
decoded = input_ids.new(output_batch_size, sent_max_len).fill_(pad_token_id)

# fill with hypothesis and eos_token_id if necessary
for i, hypo in enumerate(best):
decoded[i, : sent_lengths[i]] = hypo
if sent_lengths[i] < max_length:
decoded[i, sent_lengths[i]] = eos_token_id
else:
# none of the hypotheses have an eos_token
assert (len(hypo) == max_length for hypo in best)
decoded = torch.stack(best).type(torch.long).to(next(self.parameters()).device)

return decoded

`

Issue 2:
🚀 Feature

For "class BertEncoder" in modeling_bert.py, remove duplicate hidden_states of the last layer

Motivation

Bert-Base models have 12 layers instead of 13 layers. But when config.output_hidden_states is true, "len(all_hidden_states)" is printed 13 instead of 12. It seems that the two lines under "# Add last layer" is improper, since the last layer's hidden_states are already added.