Add unit tests for token alignment

outlines/fsm/fsm.py

@@ -423,7 +423,7 @@ def find_crossing_tokens(
 ) -> Dict[int, List[int]]:
     """Find the tokens that could replace one or more tokens at the end of token_ids
     while conserving the same intial text (and extending it by at least one character).
-    Return a dictionary with, for the indexes in the token_ids, the associated crossing tokens.
+    Return a dictionary with, for the indexes in the token_ids with matches, the associated crossing tokens.
     """
     reversed_vocabulary = {value: key for key, value in vocabulary.items()}
     len_token_ids = len(token_ids)
@@ -441,7 +441,8 @@ def find_crossing_tokens(
             if text.startswith(characters_considered)
             and len(text) > len(characters_considered)
         ]
-        crossing_tokens_map[len_token_ids - index - 1] = crossing_token_ids
+        if crossing_token_ids:
+            crossing_tokens_map[len_token_ids - index - 1] = crossing_token_ids
 
     return crossing_tokens_map
 

outlines/generate/api.py

@@ -1,8 +1,8 @@
-from typing import Iterator, List, Optional, Union
+from typing import Iterator, List, Optional, Tuple, Union
 
 import torch
 
-from outlines.fsm.fsm import FSMState
+from outlines.fsm.fsm import FSM, FSMState
 from outlines.generate.generator import sequence_generator
 
 
@@ -21,6 +21,53 @@ def __init__(
         self.device = device
         self.num_samples = sampler.samples
 
+    def align_prompt_tokens(
+        self,
+        prompt_token_ids: torch.Tensor,
+        attention_masks: torch.Tensor,
+        fsms: List[FSM],
+    ) -> Tuple[torch.Tensor, torch.Tensor]:
+        """Implement token alignment for each fsm. Return the updated tokens_ids and attention_masks"""
+        aligned_prompts, aligned_masks = zip(
+            *[
+                fsm.align_prompt_tokens(prompt, mask)
+                for prompt, mask, fsm in zip(prompt_token_ids, attention_masks, fsms)
+            ]
+        )
+        # We have to pad some of the prompts if they are not all of the same length after this operation
+        max_length_aligned_prompt = max(prompt.shape[0] for prompt in aligned_prompts)
+        padded_aligned_prompts = [
+            torch.cat(
+                [
+                    torch.full(
+                        (max_length_aligned_prompt - prompt.shape[0],),
+                        0,
+                        device=prompt_token_ids.device,
+                        dtype=prompt.dtype,
+                    ),
+                    prompt,
+                ]
+            )
+            for prompt in aligned_prompts
+        ]
+        padded_aligned_masks = [
+            torch.cat(
+                [
+                    torch.full(
+                        (max_length_aligned_prompt - mask.shape[0],),
+                        0,
+                        device=prompt_token_ids.device,
+                        dtype=mask.dtype,
+                    ),
+                    mask,
+                ]
+            )
+            for mask in aligned_masks
+        ]
+        aligned_prompt_token_ids = torch.stack(padded_aligned_prompts)
+        aligned_attention_masks = torch.stack(padded_aligned_masks)
+        return aligned_prompt_token_ids, aligned_attention_masks
+
     def get_generated_token_ids(
         self,
         prompt_token_ids: torch.Tensor,
@@ -189,49 +236,15 @@ def __call__(
         num_samples = self.num_samples
         batch_size = len(prompts)
 
-        fsm_states = [FSMState(0) for _ in range(batch_size * num_samples)]
-        fsms = [self.fsm.copy() for _ in range(batch_size * num_samples)]
-
         prompt_token_ids = torch.repeat_interleave(prompt_token_ids, num_samples, dim=0)
         attention_masks = torch.repeat_interleave(attention_masks, num_samples, dim=0)
 
-        # Token alignment may shorten some of the prompts by removing tokens at their end.
-        # We have to pad some of the prompts if they are not all of the same length after this operation
-        aligned_prompts, aligned_masks = zip(
-            *[
-                fsm.align_prompt_tokens(prompt, mask)
-                for prompt, mask, fsm in zip(prompt_token_ids, attention_masks, fsms)
-            ]
+        fsm_states = [FSMState(0) for _ in range(batch_size * num_samples)]
+        fsms = [self.fsm.copy() for _ in range(batch_size * num_samples)]
+
+        aligned_prompt_token_ids, aligned_attention_masks = self.align_prompt_tokens(
+            prompt_token_ids, attention_masks, fsms
         )
-        max_length_aligned_prompt = max(prompt.shape[0] for prompt in aligned_prompts)
-        padded_aligned_prompts = [
-            torch.cat(
-                [
-                    torch.full(
-                        (max_length_aligned_prompt - prompt.shape[0],),
-                        0,
-                        dtype=prompt.dtype,
-                    ),
-                    prompt,
-                ]
-            )
-            for prompt in aligned_prompts
-        ]
-        padded_aligned_masks = [
-            torch.cat(
-                [
-                    torch.full(
-                        (max_length_aligned_prompt - mask.shape[0],),
-                        0,
-                        dtype=mask.dtype,
-                    ),
-                    mask,
-                ]
-            )
-            for mask in aligned_masks
-        ]
-        aligned_prompt_token_ids = torch.stack(padded_aligned_prompts)
-        aligned_attention_masks = torch.stack(padded_aligned_masks)
 
         weights = torch.zeros(
             (batch_size * num_samples), dtype=torch.float, device=self.device