[Model] Use explicit types in get_generation_prompt (#33551)

Signed-off-by: DarkLight1337 <tlleungac@connect.ust.hk>

vllm/model_executor/models/whisper.py

@@ -5,7 +5,7 @@ import enum
 import math
 from collections.abc import Iterable, Mapping, Sequence
 from contextlib import nullcontext
-from typing import Annotated, Literal, cast
+from typing import Annotated, Literal
 
 import numpy as np
 import torch
@@ -21,7 +21,7 @@ from vllm.compilation.decorators import support_torch_compile
 from vllm.config import CacheConfig, ModelConfig, SpeechToTextConfig, VllmConfig
 from vllm.config.multimodal import BaseDummyOptions
 from vllm.distributed import get_tensor_model_parallel_world_size
-from vllm.inputs.data import PromptType
+from vllm.inputs.data import ExplicitEncoderDecoderPrompt, PromptType, TextPrompt
 from vllm.logger import init_logger
 from vllm.model_executor.layers.activation import get_act_fn
 from vllm.model_executor.layers.attention import (
@@ -815,21 +815,18 @@ class WhisperForConditionalGeneration(
             raise ValueError(
                 "Language must be specified when creating the Whisper prompt"
             )
-        prompt = {
-            "encoder_prompt": {
-                # Whisper does not support encoder prompt.
-                "prompt": "",
-                "multi_modal_data": {
-                    "audio": (audio, stt_config.sample_rate),
-                },
-            },
-            "decoder_prompt": (
-                (f"<|prev|>{request_prompt}" if request_prompt else "")
-                + f"<|startoftranscript|><|{language}|>"
-                + f"<|{task_type}|><|notimestamps|>"
+
+        decoder_text = (
+            f"<|prev|>{request_prompt}" if request_prompt else ""
+        ) + f"<|startoftranscript|><|{language}|><|{task_type}|><|notimestamps|>"
+
+        return ExplicitEncoderDecoderPrompt(
+            encoder_prompt=TextPrompt(
+                prompt="",  # Whisper does not support encoder prompt.
+                multi_modal_data={"audio": (audio, stt_config.sample_rate)},
             ),
-        }
-        return cast(PromptType, prompt)
+            decoder_prompt=TextPrompt(prompt=decoder_text),
+        )
 
     @classmethod
     def get_placeholder_str(cls, modality: str, i: int) -> str | None: