Generate: min length can't be larger than max length (#16668)

* min length must be smaller than max length

* Update min_length in tests

Author: gante

src/transformers/generation_flax_utils.py

@@ -259,6 +259,7 @@ def generate(
         ```"""
         # set init values
         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
         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
@@ -269,6 +270,11 @@ def generate(
 
         if decoder_start_token_id is None and self.config.is_encoder_decoder:
             raise ValueError("`decoder_start_token_id` has to be defined for encoder-decoder generation.")
+        if min_length is not None and min_length > max_length:
+            raise ValueError(
+                f"Unfeasable length constraints: the minimum length ({min_length}) is larger than the maximum "
+                f"length ({max_length})"
+            )
 
         if self.config.is_encoder_decoder:
             # add encoder_outputs to model_kwargs
@@ -389,7 +395,6 @@ def _get_logits_processor(
         no_repeat_ngram_size = (
             no_repeat_ngram_size if no_repeat_ngram_size is not None else self.config.no_repeat_ngram_size
         )
-        min_length = min_length if min_length is not None else self.config.min_length
         eos_token_id = eos_token_id if eos_token_id is not None else self.config.eos_token_id
         forced_bos_token_id = (
             forced_bos_token_id if forced_bos_token_id is not None else self.config.forced_bos_token_id

src/transformers/generation_tf_utils.py

@@ -1489,6 +1489,11 @@ def _generate(
         if pad_token_id is None and eos_token_id is not None:
             logger.warning(f"Setting `pad_token_id` to {eos_token_id} (first `eos_token_id`) to generate sequence")
             pad_token_id = eos_token_id
+        if min_length is not None and min_length > max_length:
+            raise ValueError(
+                f"Unfeasable length constraints: the minimum length ({min_length}) is larger than the maximum "
+                f"length ({max_length})"
+            )
 
         # 2. Define model inputs
         input_ids = self._prepare_model_inputs(input_ids, bos_token_id)

src/transformers/generation_utils.py

@@ -700,7 +700,6 @@ def _get_logits_processor(
             else self.config.encoder_no_repeat_ngram_size
         )
         bad_words_ids = bad_words_ids if bad_words_ids is not None else self.config.bad_words_ids
-        min_length = min_length if min_length is not None else self.config.min_length
         eos_token_id = eos_token_id if eos_token_id is not None else self.config.eos_token_id
         diversity_penalty = diversity_penalty if diversity_penalty is not None else self.config.diversity_penalty
         forced_bos_token_id = (
@@ -1185,7 +1184,13 @@ def generate(
             )
         # default to config if still None
         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
 
+        if min_length is not None and min_length > max_length:
+            raise ValueError(
+                f"Unfeasable length constraints: the minimum length ({min_length}) is larger than the maximum "
+                f"length ({max_length})"
+            )
         if input_ids_seq_length >= max_length:
             input_ids_string = "decoder_input_ids" if self.config.is_encoder_decoder else "input_ids"
             logger.warning(

tests/generation/test_generation_utils.py

@@ -102,7 +102,7 @@ def _get_logits_processor_and_kwargs(
         diversity_penalty=None,
     ):
         process_kwargs = {
-            "min_length": input_length + 1,
+            "min_length": input_length + 1 if max_length is None else max_length - 1,
             "bad_words_ids": [[1, 0]],
             "no_repeat_ngram_size": 2,
             "repetition_penalty": 1.2,