[Bug]: MiniCPM5 chat template may lose text after <tool_sep> due to loop-local assignments

[harelhuang]

Is there an existing issue?

• I searched existing issues for tool_sep, processed_content, chat_template, and jinja and did not find this problem reported.

Describe the bug

MiniCPM5-2B's chat template appears to use loop-local set assignments to accumulate processed_content for use after the loops. Jinja2 does not propagate these assignments to the enclosing scope.

With assistant content BEFORE<tool_sep>AFTER and one tool call, the rendered prompt loses AFTER. The tool XML is emitted once by the later direct-output branch.

Template: openbmb/MiniCPM5-2B/chat_template.jinja, revision a063f08de1bd09dfc9ae4cf3da35e6064949e533.

To reproduce

Download the unchanged template as chat_template.jinja, then run this script in the same directory. It only requires Jinja2; no model weights or inference are involved.

from pathlib import Path

from jinja2 import Environment


template = Environment(trim_blocks=True, lstrip_blocks=True).from_string(
    Path("chat_template.jinja").read_text(encoding="utf-8")
)

for content in ["BEFORE", "BEFORE<tool_sep>AFTER"]:
    output = template.render(
        bos_token="",
        tools=[],
        messages=[
            {"role": "user", "content": "Question"},
            {
                "role": "assistant",
                "content": content,
                "tool_calls": [
                    {
                        "function": {
                            "name": "lookup",
                            "arguments": {"q": "weather"},
                        }
                    }
                ],
            },
        ],
        add_generation_prompt=False,
    )
    print("Input:", content)
    print("Contains AFTER:", "AFTER" in output)
    print("Tool XML count:", output.count('<function name="'))
    print(repr(output))

Observed output:

Input: BEFORE
Contains AFTER: False
Tool XML count: 1
'<|im_start|>user\nQuestion<|im_end|>\n<|im_start|>assistant\n<think>\n\n</think>\n\nBEFORE\n<function name="lookup"><param name="q">weather</param></function><|im_end|>\n'
Input: BEFORE<tool_sep>AFTER
Contains AFTER: False
Tool XML count: 1
'<|im_start|>user\nQuestion<|im_end|>\n<|im_start|>assistant\n<think>\n\n</think>\n\nBEFORE\n<function name="lookup"><param name="q">weather</param></function><|im_end|>\n'

Expected behavior

Assuming <tool_sep> marks an in-place tool-call position, I would expect both surrounding text segments to survive, with the tool XML inserted between BEFORE and AFTER. Could you confirm whether this is the intended behavior?

Environment

• Python 3.12.2
• Jinja2 3.1.3
• Direct rendering of the unchanged template with Environment(trim_blocks=True, lstrip_blocks=True)

Additional context

The assignments at template lines 84, 86, and 112 are inside nested loops. When line 116 reads processed_content, its enclosing value remains content_parts[0]. Jinja documents this assignment-scoping behavior and the use of namespace objects for cross-scope state.

The final tool-output condition at line 127 also reads has_tool_sep, which is not defined anywhere in this template or supplied by this reproducer. The condition is therefore true for the tool-calling messages above. If accumulation is changed to persist across loops, that final output condition should be reviewed together with it so that each tool call is emitted once.