Strengthen input validation and tests for 'parse_raw_prompts’. (#30652)

Signed-off-by: Kayvan Mivehnejad <K.Mivehnejad@gmail.com>

vllm/inputs/parse.py

@@ -45,16 +45,17 @@ def parse_raw_prompts(
 
         # case 4: array of token arrays
         if is_list_of(prompt, list):
-            first = prompt[0]
-            if not isinstance(first, list):
-                raise ValueError("prompt expected to be a list of lists")
-
-            if len(first) == 0:
-                raise ValueError("Please provide at least one prompt")
-
-            # strict validation: every nested list must be list[int]
-            if not all(is_list_of(elem, int) for elem in prompt):
-                raise TypeError("Nested lists must contain only integers")
+            if len(prompt) == 1 and isinstance(prompt[0], list) and len(prompt[0]) == 0:
+                raise ValueError("please provide at least one prompt")
+            for elem in prompt:
+                if not isinstance(elem, list):
+                    raise TypeError(
+                        "prompt must be a list of lists, but found a non-list element."
+                    )
+                if not is_list_of(elem, int):
+                    raise TypeError(
+                        "Nested lists of tokens must contain only integers."
+                    )
 
             prompt = cast(list[list[int]], prompt)
             return [TokensPrompt(prompt_token_ids=elem) for elem in prompt]