[whisper] Clarify error message when setting max_new_tokens (#33324)

* clarify error message when setting max_new_tokens

* sync error message in test_generate_with_prompt_ids_max_length

* there is no self

src/transformers/models/whisper/generation_whisper.py

@@ -1698,8 +1698,8 @@ def _set_max_new_tokens_and_length(self, config, decoder_input_ids, generation_c
         max_new_tokens = generation_config.max_new_tokens if generation_config.max_new_tokens is not None else 0
         if max_new_tokens + decoder_input_ids.shape[-1] > self.config.max_target_positions:
             raise ValueError(
-                f"The length of `decoder_input_ids` equal `prompt_ids` plus special start tokens is {decoder_input_ids.shape[-1]}, and the `max_new_tokens` "
-                f"is {max_new_tokens}. Thus, the combined length of "
+                f"The length of `decoder_input_ids`, including special start tokens, prompt tokens, and previous tokens, is {decoder_input_ids.shape[-1]}, "
+                f" and `max_new_tokens` is {max_new_tokens}. Thus, the combined length of "
                 f"`decoder_input_ids` and `max_new_tokens` is: {max_new_tokens + decoder_input_ids.shape[-1]}. This exceeds the "
                 f"`max_target_positions` of the Whisper model: {self.config.max_target_positions}. "
                 "You should either reduce the length of your prompt, or reduce the value of `max_new_tokens`, "

tests/models/whisper/test_modeling_whisper.py

@@ -1349,8 +1349,8 @@ def test_generate_with_prompt_ids_max_length(self):
 
         with self.assertRaisesRegex(
             ValueError,
-            f"The length of `decoder_input_ids` equal `prompt_ids` plus special start tokens is {decoder_input_ids.shape[-1]}, and the `max_new_tokens` "
-            f"is {max_new_tokens}. Thus, the combined length of "
+            f"The length of `decoder_input_ids`, including special start tokens, prompt tokens, and previous tokens, is {decoder_input_ids.shape[-1]}, "
+            f" and `max_new_tokens` is {max_new_tokens}. Thus, the combined length of "
             f"`decoder_input_ids` and `max_new_tokens` is: {max_new_tokens + decoder_input_ids.shape[-1]}. This exceeds the "
             f"`max_target_positions` of the Whisper model: {config.max_target_positions}. "
             "You should either reduce the length of your prompt, or reduce the value of `max_new_tokens`, "