Sync from v0.13

vllm/beam_search.py

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+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+from dataclasses import dataclass
+from typing import TYPE_CHECKING, Any, Optional
+
+from vllm.logprobs import Logprob
+from vllm.lora.request import LoRARequest
+
+if TYPE_CHECKING:
+    from vllm.multimodal import MultiModalDataDict
+
+
+@dataclass
+class BeamSearchSequence:
+    """A sequence for beam search.
+    It keeps track of the tokens and the log probability of the sequence.
+    The text field is optional and will only be filled when the sequence is
+    about to be returned to the user.
+    """
+
+    # The tokens include the prompt.
+    tokens: list[int]
+    logprobs: list[dict[int, Logprob]]
+    lora_request: LoRARequest | None = None
+    cum_logprob: float = 0.0
+    text: str | None = None
+    finish_reason: str | None = None
+    stop_reason: int | str | None = None
+    multi_modal_data: Optional["MultiModalDataDict"] = None
+    mm_processor_kwargs: dict[str, Any] | None = None
+
+
+@dataclass
+class BeamSearchOutput:
+    """The output of beam search.
+    It contains the list of the best beam search sequences.
+    The length of the list is equal to the beam width.
+    """
+
+    sequences: list[BeamSearchSequence]
+
+
+class BeamSearchInstance:
+    def __init__(
+        self,
+        prompt_tokens: list[int],
+        lora_request: LoRARequest | None = None,
+        logprobs: list[dict[int, Logprob]] | None = None,
+        **kwargs,
+    ):
+        self.beams: list[BeamSearchSequence] = [
+            BeamSearchSequence(
+                tokens=prompt_tokens,
+                logprobs=[] if logprobs is None else list(logprobs),
+                lora_request=lora_request,
+                **kwargs,
+            )
+        ]
+        self.completed: list[BeamSearchSequence] = []
+
+
+def get_beam_search_score(
+    tokens: list[int],
+    cumulative_logprob: float,
+    eos_token_id: int,
+    length_penalty: float = 1.0,
+) -> float:
+    """Calculate the beam search score with length penalty.
+
+    Adapted from
+
+    https://github.com/huggingface/transformers/blob/ccb92be23def445f2afdea94c31286f84b89eb5b/src/transformers/generation/beam_search.py#L938
+    """
+    seq_len = len(tokens)
+    if tokens[-1] == eos_token_id:
+        seq_len -= 1
+
+    return cumulative_logprob / (seq_len**length_penalty)
+
+
+def create_sort_beams_key_function(eos_token_id: int, length_penalty: float):
+    def sort_beams_key(x: BeamSearchSequence) -> float:
+        return get_beam_search_score(
+            x.tokens, x.cum_logprob, eos_token_id, length_penalty
+        )
+
+    return sort_beams_key