ruiling-smartbear · Sep 6, 2026
diff --git a/tests/utils/deepseek_r1_chat_template.jinja b/tests/utils/deepseek_r1_chat_template.jinja
@@ -0,0 +1 @@
+{% if not add_generation_prompt is defined %}{% set add_generation_prompt = false %}{% endif %}{% set ns = namespace(is_first=false, is_tool=false, is_output_first=true, system_prompt='') %}{%- for message in messages %}{%- if message['role'] == 'system' %}{% set ns.system_prompt = message['content'] %}{%- endif %}{%- endfor %}{{bos_token}}{{ns.system_prompt}}{%- for message in messages %}{%- if message['role'] == 'user' %}{%- set ns.is_tool = false -%}{{'<｜User｜>' + message['content']}}{%- endif %}{%- if message['role'] == 'assistant' and message['content'] is none %}{%- set ns.is_tool = false -%}{%- for tool in message['tool_calls']%}{%- if not ns.is_first %}{{'<｜Assistant｜><｜tool▁calls▁begin｜><｜tool▁call▁begin｜>' + tool['type'] + '<｜tool▁sep｜>' + tool['function']['name'] + '\n' + '```json' + '\n' + tool['function']['arguments'] + '\n' + '```' + '<｜tool▁call▁end｜>'}}{%- set ns.is_first = true -%}{%- else %}{{'\n' + '<｜tool▁call▁begin｜>' + tool['type'] + '<｜tool▁sep｜>' + tool['function']['name'] + '\n' + '```json' + '\n' + tool['function']['arguments'] + '\n' + '```' + '<｜tool▁call▁end｜>'}}{{'<｜tool▁calls▁end｜><｜end▁of▁sentence｜>'}}{%- endif %}{%- endfor %}{%- endif %}{%- if message['role'] == 'assistant' and message['content'] is not none %}{%- if ns.is_tool %}{{'<｜tool▁outputs▁end｜>' + message['content'] + '<｜end▁of▁sentence｜>'}}{%- set ns.is_tool = false -%}{%- else %}{% set content = message['content'] %}{% if '</think>' in content %}{% set content = content.split('</think>')[-1] %}{% endif %}{{'<｜Assistant｜>' + content + '<｜end▁of▁sentence｜>'}}{%- endif %}{%- endif %}{%- if message['role'] == 'tool' %}{%- set ns.is_tool = true -%}{%- if ns.is_output_first %}{{'<｜tool▁outputs▁begin｜><｜tool▁output▁begin｜>' + message['content'] + '<｜tool▁output▁end｜>'}}{%- set ns.is_output_first = false %}{%- else %}{{'\n<｜tool▁output▁begin｜>' + message['content'] + '<｜tool▁output▁end｜>'}}{%- endif %}{%- endif %}{%- endfor -%}{% if ns.is_tool %}{{'<｜tool▁outputs▁end｜>'}}{% endif %}{% if add_generation_prompt and not ns.is_tool %}{{'<｜Assistant｜><think>\n'}}{% endif %}
diff --git a/tests/utils/test_chat_template_tool_arguments_on_cpu.py b/tests/utils/test_chat_template_tool_arguments_on_cpu.py
@@ -0,0 +1,295 @@
+# Copyright 2025 Bytedance Ltd. and/or its affiliates
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import copy
+import json
+import os
+
+import pytest
+from jinja2.sandbox import ImmutableSandboxedEnvironment
+from transformers.utils.chat_template_utils import render_jinja_template
+
+from verl.utils.tokenizer.chat_template import apply_chat_template, tool_call_arguments_as_json
+
+# The tool-call branch of the DeepSeek-V3.1 chat template as shipped in its
+# tokenizer_config.json: ``tool['function']['arguments']`` is concatenated into the
+# prompt without ``| tojson``, so a mapping raises TypeError inside Jinja. R1 and V3
+# do the same inside a ```json block.
+_DEEPSEEK_V31_TOOL_CALL_TEMPLATE = (
+    "{{ bos_token }}"
+    "{%- for message in messages -%}"
+    "{%- if message['role'] == 'user' -%}{{'<｜User｜>' + message['content']}}{%- endif -%}"
+    "{%- if message['role'] == 'assistant' and message['tool_calls'] -%}"
+    "{{'<｜Assistant｜><think></think>'}}"
+    "{%- for tool in message['tool_calls'] -%}"
+    "{{'<｜tool▁calls▁begin｜><｜tool▁call▁begin｜>' + tool['function']['name'] + '<｜tool▁sep｜>'"
+    " + tool['function']['arguments'] + '<｜tool▁call▁end｜>'}}"
+    "{%- endfor -%}"
+    "{{'<｜tool▁calls▁end｜><｜end▁of▁sentence｜>'}}"
+    "{%- endif -%}"
+    "{%- if message['role'] == 'tool' -%}"
+    "{{'<｜tool▁output▁begin｜>' + message['content'] + '<｜tool▁output▁end｜>'}}"
+    "{%- endif -%}"
+    "{%- endfor -%}"
+)
+
+
+class _RecordingTokenizer:
+    """Records every message list handed to ``apply_chat_template``."""
+
+    name_or_path = "unit-test/recording"
+
+    def __init__(self):
+        self.seen = []
+
+    def render(self, messages, add_generation_prompt):
+        raise NotImplementedError
+
+    def apply_chat_template(
+        self, messages, tokenize=True, add_generation_prompt=True, tools=None, return_dict=False, **kwargs
+    ):
+        self.seen.append(messages)
+        rendered = self.render(messages, add_generation_prompt)
+        if tokenize:
+            return [ord(char) for char in rendered]
+        return rendered
+
+
+class _ConcatenatingTokenizer(_RecordingTokenizer):
+    """Splices tool-call arguments in by string concatenation, like DeepSeek-R1 / V3 / V3.1."""
+
+    def render(self, messages, add_generation_prompt):
+        rendered = ""
+        for message in messages:
+            if message["role"] == "assistant" and message.get("tool_calls"):
+                for tool_call in message["tool_calls"]:
+                    function = tool_call["function"]
+                    rendered += "<call>" + function["name"] + "\n```json\n" + function["arguments"] + "\n```</call>"
+                continue
+            rendered += f"<{message['role']}>" + message.get("content", "")
+        if add_generation_prompt:
+            rendered += "<assistant>"
+        return rendered
+
+
+class _JsonFilterTokenizer(_RecordingTokenizer):
+    """Renders tool-call arguments through ``| tojson``, like Qwen and Llama templates."""
+
+    def render(self, messages, add_generation_prompt):
+        rendered = ""
+        for message in messages:
+            if message["role"] == "assistant" and message.get("tool_calls"):
+                for tool_call in message["tool_calls"]:
+                    function = tool_call["function"]
+                    rendered += "<call>" + json.dumps({"name": function["name"], "arguments": function["arguments"]})
+                continue
+            rendered += f"<{message['role']}>" + message.get("content", "")
+        if add_generation_prompt:
+            rendered += "<assistant>"
+        return rendered
+
+
+class _JinjaTokenizer:
+    """Renders through a sandboxed Jinja environment, the way transformers does."""
+
+    name_or_path = "unit-test/deepseek-v3.1-tool-branch"
+    bos_token = "<｜begin▁of▁sentence｜>"
+
+    def __init__(self, template=_DEEPSEEK_V31_TOOL_CALL_TEMPLATE):
+        self._template = ImmutableSandboxedEnvironment().from_string(template)
+
+    def apply_chat_template(
+        self, messages, tokenize=True, add_generation_prompt=True, tools=None, return_dict=False, **kwargs
+    ):
+        rendered = self._template.render(
+            messages=messages, bos_token=self.bos_token, add_generation_prompt=add_generation_prompt
+        )
+        if tokenize:
+            return [ord(char) for char in rendered]
+        return rendered
+
+
+def _tool_call_history(arguments):
+    return [
+        {"role": "user", "content": "Weather in Seattle?"},
+        {
+            "role": "assistant",
+            "content": "",
+            "tool_calls": [
+                {"id": "c0", "type": "function", "function": {"name": "get_weather", "arguments": arguments}}
+            ],
+        },
+        {"role": "tool", "content": "rain", "tool_call_id": "c0"},
+    ]
+
+
+def test_tool_call_arguments_as_json_serializes_only_mappings():
+    messages = _tool_call_history({"city": "Seattle"})
+    original = copy.deepcopy(messages)
+
+    converted, changed = tool_call_arguments_as_json(messages)
+
+    assert changed
+    assert converted[1]["tool_calls"][0]["function"]["arguments"] == '{"city": "Seattle"}'
+    assert converted[1]["tool_calls"][0]["id"] == "c0"
+    # Untouched messages are the same objects; the input is not mutated.
+    assert converted[0] is messages[0]
+    assert converted[2] is messages[2]
+    assert messages == original
+
+
+def test_tool_call_arguments_as_json_reports_nothing_to_convert():
+    messages = _tool_call_history('{"city": "Seattle"}')
+
+    converted, changed = tool_call_arguments_as_json(messages)
+
+    assert not changed
+    assert converted == messages
+    assert all(after is before for after, before in zip(converted, messages, strict=True))
+
+
+def test_tool_call_arguments_as_json_keeps_non_ascii_and_nesting():
+    messages = _tool_call_history({"query": "天气", "ids": [1, 2], "opts": {"unit": "c"}})
+
+    converted, _ = tool_call_arguments_as_json(messages)
+
+    expected = '{"query": "天气", "ids": [1, 2], "opts": {"unit": "c"}}'
+    assert converted[1]["tool_calls"][0]["function"]["arguments"] == expected
+
+
+@pytest.mark.parametrize("tokenize", [False, True])
+def test_mapping_arguments_render_through_a_concatenating_template(tokenize):
+    tokenizer = _ConcatenatingTokenizer()
+    messages = _tool_call_history({"city": "Seattle"})
+    original = copy.deepcopy(messages)
+
+    output = apply_chat_template(tokenizer, messages, tokenize=tokenize, add_generation_prompt=True)
+
+    expected = (
+        '<user>Weather in Seattle?<call>get_weather\n```json\n{"city": "Seattle"}\n```</call><tool>rain<assistant>'
+    )
+    assert output == ([ord(char) for char in expected] if tokenize else expected)
+    # One failed attempt with the mapping, one retry with the JSON string.
+    assert len(tokenizer.seen) == 2
+    assert tokenizer.seen[0][1]["tool_calls"][0]["function"]["arguments"] == {"city": "Seattle"}
+    assert tokenizer.seen[1][1]["tool_calls"][0]["function"]["arguments"] == '{"city": "Seattle"}'
+    assert messages == original
+
+
+def test_string_arguments_render_in_one_attempt():
+    tokenizer = _ConcatenatingTokenizer()
+    messages = _tool_call_history('{"city": "Seattle"}')
+
+    output = apply_chat_template(tokenizer, messages, tokenize=False, add_generation_prompt=False)
+
+    assert output == '<user>Weather in Seattle?<call>get_weather\n```json\n{"city": "Seattle"}\n```</call><tool>rain'
+    assert len(tokenizer.seen) == 1
+
+
+def test_templates_that_render_mappings_receive_the_mapping():
+    tokenizer = _JsonFilterTokenizer()
+    messages = _tool_call_history({"city": "Seattle"})
+
+    output = apply_chat_template(tokenizer, messages, tokenize=False, add_generation_prompt=False)
+
+    assert output == (
+        '<user>Weather in Seattle?<call>{"name": "get_weather", "arguments": {"city": "Seattle"}}<tool>rain'
+    )
+    assert len(tokenizer.seen) == 1
+    assert tokenizer.seen[0] is messages
+
+
+def test_deepseek_v31_tool_branch_renders_mapping_arguments_under_jinja():
+    tokenizer = _JinjaTokenizer()
+    messages = _tool_call_history({"city": "Seattle"})
+
+    # The template alone rejects the mapping, with the error the DeepSeek templates raise.
+    with pytest.raises(TypeError, match="can only concatenate str"):
+        tokenizer.apply_chat_template(messages, tokenize=False)
+
+    output = apply_chat_template(tokenizer, messages, tokenize=False, add_generation_prompt=False)
+
+    assert output == (
+        "<｜begin▁of▁sentence｜><｜User｜>Weather in Seattle?<｜Assistant｜><think></think>"
+        '<｜tool▁calls▁begin｜><｜tool▁call▁begin｜>get_weather<｜tool▁sep｜>{"city": "Seattle"}<｜tool▁call▁end｜>'
+        "<｜tool▁calls▁end｜><｜end▁of▁sentence｜><｜tool▁output▁begin｜>rain<｜tool▁output▁end｜>"
+    )
+
+
+class _OfficialTemplateTokenizer:
+    """Renders the DeepSeek-R1 chat template through transformers' own Jinja path.
+
+    The template is the ``chat_template`` from the DeepSeek-R1 distill checkpoints'
+    ``tokenizer_config.json``; DeepSeek-V3 shares its tool-call branch. The tool-call
+    branch only runs for assistant messages whose ``content`` is ``None``, and it
+    concatenates ``tool['function']['arguments']`` into the prompt.
+    """
+
+    name_or_path = "unit-test/deepseek-r1"
+    bos_token = "<｜begin▁of▁sentence｜>"
+    eos_token = "<｜end▁of▁sentence｜>"
+
+    def __init__(self):
+        template_path = os.path.join(os.path.dirname(__file__), "deepseek_r1_chat_template.jinja")
+        with open(template_path, encoding="utf-8") as template_file:
+            self.chat_template = template_file.read()
+
+    def apply_chat_template(
+        self, messages, tokenize=True, add_generation_prompt=True, tools=None, return_dict=False, **kwargs
+    ):
+        rendered, _ = render_jinja_template(
+            conversations=[messages],
+            tools=tools,
+            chat_template=self.chat_template,
+            add_generation_prompt=add_generation_prompt,
+            bos_token=self.bos_token,
+            eos_token=self.eos_token,
+            **kwargs,
+        )
+        rendered = rendered[0]
+        if tokenize:
+            return [ord(char) for char in rendered]
+        return rendered
+
+
+def test_official_deepseek_r1_template_renders_mapping_arguments():
+    tokenizer = _OfficialTemplateTokenizer()
+    messages = _tool_call_history({"city": "Seattle"})
+    messages[1]["content"] = None
+
+    with pytest.raises(TypeError, match="can only concatenate str"):
+        tokenizer.apply_chat_template(messages, tokenize=False)
+
+    output = apply_chat_template(tokenizer, messages, tokenize=False, add_generation_prompt=False)
+
+    assert output == (
+        "<｜begin▁of▁sentence｜><｜User｜>Weather in Seattle?"
+        "<｜Assistant｜><｜tool▁calls▁begin｜><｜tool▁call▁begin｜>function<｜tool▁sep｜>get_weather\n"
+        '```json\n{"city": "Seattle"}\n```<｜tool▁call▁end｜>'
+        "<｜tool▁outputs▁begin｜><｜tool▁output▁begin｜>rain<｜tool▁output▁end｜><｜tool▁outputs▁end｜>"
+    )
+    assert messages[1]["tool_calls"][0]["function"]["arguments"] == {"city": "Seattle"}
+
+
+def test_type_errors_unrelated_to_arguments_still_propagate():
+    class _BrokenTokenizer(_RecordingTokenizer):
+        def render(self, messages, add_generation_prompt):
+            raise TypeError("boom")
+
+    tokenizer = _BrokenTokenizer()
+
+    with pytest.raises(TypeError, match="boom"):
+        apply_chat_template(tokenizer, _tool_call_history({"city": "Seattle"}), tokenize=False)
+    with pytest.raises(TypeError, match="boom"):
+        apply_chat_template(tokenizer, _tool_call_history('{"city": "Seattle"}'), tokenize=False)
diff --git a/tests/utils/test_continuous_token_on_cpu.py b/tests/utils/test_continuous_token_on_cpu.py
@@ -641,18 +641,51 @@ def test_deepseek_builder_renders_tool_appends_through_string_concatenating_temp
     ]
     updated_messages = previous_messages + [{"role": "tool", "content": "answer", "tool_call_id": "call_0"}]
 
-    # The base synthetic tool call carries a mapping, which this template family cannot splice in.
-    with pytest.raises(TypeError):
-        ContinuousTokenBuilder(tokenizer).tokenize_non_assistant_incremental_messages(
-            previous_messages, updated_messages
-        )
-
     assert isinstance(builder, DeepSeekContinuousTokenBuilder)
     incremental = builder.tokenize_non_assistant_incremental_messages(previous_messages, updated_messages)
 
     # Only the tool output: DeepSeek templates add no generation prompt after a tool message.
     assert incremental == [ord(char) for char in "<tool_output_begin>answer<tool_output_end>"]
 
+    # The base synthetic tool call carries a mapping. apply_chat_template serializes it
+    # for this template family, so the default builder renders the same append.
+    base_incremental = ContinuousTokenBuilder(tokenizer).tokenize_non_assistant_incremental_messages(
+        previous_messages, updated_messages
+    )
+    assert base_incremental == incremental
+
+
+def test_deepseek_builder_renders_history_with_mapping_tool_call_arguments():
+    tokenizer = _DeepSeekBoundaryTokenizer()
+    builder = create_continuous_token_builder(tokenizer, model_family="deepseek")
+    messages = [
+        {"role": "user", "content": "question"},
+        {
+            "role": "assistant",
+            "content": "",
+            "tool_calls": [
+                {"id": "call_0", "type": "function", "function": {"name": "lookup", "arguments": {"q": "x"}}}
+            ],
+        },
+        {"role": "tool", "content": "answer", "tool_call_id": "call_0"},
+        {"role": "assistant", "content": "done"},
+        {"role": "user", "content": "next"},
+    ]
+
+    initial = builder.build_initial_tokens(messages)
+
+    expected = (
+        "<user>question\n"
+        '<assistant><tool_call_begin>lookup<tool_sep>{"q": "x"}<tool_call_end><eos>'
+        "<tool_output_begin>answer<tool_output_end>"
+        "<assistant>done\n"
+        "<user>next\n"
+        "<assistant>"
+    )
+    assert initial == [ord(char) for char in expected]
+    # The history itself is left as verl stores it.
+    assert messages[1]["tool_calls"][0]["function"]["arguments"] == {"q": "x"}
+
 
 def test_deepseek_builder_synthetic_tool_call_arguments_are_a_json_string():
     builder = DeepSeekContinuousTokenBuilder(_DeepSeekBoundaryTokenizer())
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		{% if not add_generation_prompt is defined %}{% set add_generation_prompt = false %}{% endif %}{% set ns = namespace(is_first=false, is_tool=false, is_output_first=true, system_prompt='') %}{%- for message in messages %}{%- if message['role'] == 'system' %}{% set ns.system_prompt = message['content'] %}{%- endif %}{%- endfor %}{{bos_token}}{{ns.system_prompt}}{%- for message in messages %}{%- if message['role'] == 'user' %}{%- set ns.is_tool = false -%}{{'<｜User｜>' + message['content']}}{%- endif %}{%- if message['role'] == 'assistant' and message['content'] is none %}{%- set ns.is_tool = false -%}{%- for tool in message['tool_calls']%}{%- if not ns.is_first %}{{'<｜Assistant｜><｜tool▁calls▁begin｜><｜tool▁call▁begin｜>' + tool['type'] + '<｜tool▁sep｜>' + tool['function']['name'] + '\n' + '```json' + '\n' + tool['function']['arguments'] + '\n' + '```' + '<｜tool▁call▁end｜>'}}{%- set ns.is_first = true -%}{%- else %}{{'\n' + '<｜tool▁call▁begin｜>' + tool['type'] + '<｜tool▁sep｜>' + tool['function']['name'] + '\n' + '```json' + '\n' + tool['function']['arguments'] + '\n' + '```' + '<｜tool▁call▁end｜>'}}{{'<｜tool▁calls▁end｜><｜end▁of▁sentence｜>'}}{%- endif %}{%- endfor %}{%- endif %}{%- if message['role'] == 'assistant' and message['content'] is not none %}{%- if ns.is_tool %}{{'<｜tool▁outputs▁end｜>' + message['content'] + '<｜end▁of▁sentence｜>'}}{%- set ns.is_tool = false -%}{%- else %}{% set content = message['content'] %}{% if '</think>' in content %}{% set content = content.split('</think>')[-1] %}{% endif %}{{'<｜Assistant｜>' + content + '<｜end▁of▁sentence｜>'}}{%- endif %}{%- endif %}{%- if message['role'] == 'tool' %}{%- set ns.is_tool = true -%}{%- if ns.is_output_first %}{{'<｜tool▁outputs▁begin｜><｜tool▁output▁begin｜>' + message['content'] + '<｜tool▁output▁end｜>'}}{%- set ns.is_output_first = false %}{%- else %}{{'\n<｜tool▁output▁begin｜>' + message['content'] + '<｜tool▁output▁end｜>'}}{%- endif %}{%- endif %}{%- endfor -%}{% if ns.is_tool %}{{'<｜tool▁outputs▁end｜>'}}{% endif %}{% if add_generation_prompt and not ns.is_tool %}{{'<｜Assistant｜><think>\n'}}{% endif %}