From 19406fae287380991908d2f27fe3975ba047147d Mon Sep 17 00:00:00 2001
From: Moe Huzaifa <mhuzaifa3@outlook.com>
Date: Tue, 25 Aug 2026 11:30:23 -0500
Subject: [PATCH] [Bugfix][Tokenizer] Replace bare asserts in the DeepSeek V4
 encoder (#53747)

Signed-off-by: mhuzaifa3 <mhuzaifa3@outlook.com>
---
 tests/tokenizers_/test_deepseek_v4.py   | 24 ++++++++++++++++++++++++
 vllm/tokenizers/deepseek_v4_encoding.py | 25 +++++++++++++++++--------
 2 files changed, 41 insertions(+), 8 deletions(-)

diff --git a/tests/tokenizers_/test_deepseek_v4.py b/tests/tokenizers_/test_deepseek_v4.py
index d452d1d7fe..6fd4be9fd8 100644
--- a/tests/tokenizers_/test_deepseek_v4.py
+++ b/tests/tokenizers_/test_deepseek_v4.py
@@ -403,3 +403,27 @@ def test_deepseek_v4_matches_reference_golden_fixtures(case_id, kwargs):
 
     expected = (FIXTURES_DIR / f"test_output_{case_id}.txt").read_text()
     assert prompt == expected
+
+
+def test_deepseek_v4_rejects_empty_developer_content():
+    with pytest.raises(ValueError):
+        _tokenizer().apply_chat_template(
+            [{"role": "developer", "content": ""}],
+            tokenize=False,
+            enable_thinking=True,
+            reasoning_effort="low",
+        )
+
+
+@pytest.mark.parametrize(
+    "kwargs",
+    [
+        {"thinking_mode": "bogus"},
+        {"thinking_mode": "thinking", "reasoning_effort": "turbo"},
+    ],
+)
+def test_deepseek_v4_encode_messages_rejects_invalid_arguments(kwargs):
+    from vllm.tokenizers.deepseek_v4_encoding import encode_messages
+
+    with pytest.raises(ValueError):
+        encode_messages([{"role": "user", "content": "Hello"}], **kwargs)
diff --git a/vllm/tokenizers/deepseek_v4_encoding.py b/vllm/tokenizers/deepseek_v4_encoding.py
index 6c0f804724..1447c9de95 100644
--- a/vllm/tokenizers/deepseek_v4_encoding.py
+++ b/vllm/tokenizers/deepseek_v4_encoding.py
@@ -225,8 +225,12 @@ def render_message(
     Returns:
         Encoded string for this message.
     """
-    assert 0 <= index < len(messages)
-    assert thinking_mode in ["chat", "thinking"], f"Invalid thinking_mode `{thinking_mode}`"
+    if not (0 <= index < len(messages)):
+        raise ValueError(
+            f"Index {index} out of range for messages list of length {len(messages)}"
+        )
+    if thinking_mode not in ["chat", "thinking"]:
+        raise ValueError(f"Invalid thinking_mode `{thinking_mode}`")
 
     prompt = ""
     msg = messages[index]
@@ -248,10 +252,11 @@ def render_message(
         tool_calls = tool_calls_from_openai_format(tool_calls)
 
     reasoning_effort = reasoning_effort or DEFAULT_REASONING_EFFORT
-    assert reasoning_effort in REASONING_EFFORT_PROMPTS, (
-        f"Invalid reasoning effort: {reasoning_effort}, expected one of "
-        f"{list(REASONING_EFFORT_PROMPTS)}"
-    )
+    if reasoning_effort not in REASONING_EFFORT_PROMPTS:
+        raise ValueError(
+            f"Invalid reasoning effort: {reasoning_effort}, expected one of "
+            f"{list(REASONING_EFFORT_PROMPTS)}"
+        )
     if index == 0 and thinking_mode == "thinking":
         prompt += REASONING_EFFORT_PROMPTS[reasoning_effort]
 
@@ -263,7 +268,8 @@ def render_message(
             prompt += "\n\n" + response_format_template.format(schema=to_json(response_format))
 
     elif role == "developer":
-        assert content, f"Invalid message for role `{role}`: {msg}"
+        if not content:
+            raise ValueError(f"Invalid message for role `{role}`: {msg}")
 
         content_developer = USER_SP_TOKEN
         content_developer += content
@@ -362,7 +368,10 @@ def render_message(
     task = messages[index].get("task")
     if task is not None:
         # Task special token for internal classification tasks
-        assert task in VALID_TASKS, f"Invalid task: '{task}'. Valid tasks are: {list(VALID_TASKS)}"
+        if task not in VALID_TASKS:
+            raise ValueError(
+                f"Invalid task: '{task}'. Valid tasks are: {list(VALID_TASKS)}"
+            )
         task_sp_token = DS_TASK_SP_TOKENS[task]
 
         if task != "action":