chat_template.jinja

{{- bos_token -}}
{#-
  Fixed chat template for LiquidAI/LFM2.5-1.2B-Instruct.

  Framework-agnostic — works with HuggingFace transformers apply_chat_template(),
  vLLM, TGI, and any Jinja2-based rendering pipeline.

  Bugs fixed in the upstream HF template:
  1. content=None on assistant messages renders "null" (via tojson) instead of empty
  2. tool_calls field on assistant messages is completely ignored — multi-turn tool
     conversations lose all tool call context
  3. content=None on tool messages renders "null" instead of empty

  Tool call reconstruction: when assistant messages carry a tool_calls field (OpenAI
  format), this template reconstructs them into LFM's native format:
    <|tool_call_start|>[func_name(param="value")]<|tool_call_end|>

  Handles function.arguments as either a Python dict (pre-parsed) or a JSON string
  (OpenAI wire format). Dict arguments get full pythonic formatting; JSON strings
  are embedded as-is (best effort — no from_json filter in standard Jinja2).

  Options:
    keep_past_thinking  (default: false)  — preserve <think> blocks in non-final assistant turns

  Ref: https://docs.liquid.ai/lfm/key-concepts/tool-use
  Ref: https://huggingface.co/LiquidAI/LFM2.5-1.2B-Instruct/blob/main/chat_template.jinja
-#}
{%- set keep_past_thinking = keep_past_thinking | default(false) -%}

{#- Extract system prompt from first message if present -#}
{%- set ns = namespace(system_prompt="") -%}
{%- if messages[0]["role"] == "system" -%}
    {%- set ns.system_prompt = messages[0]["content"] -%}
    {%- set messages = messages[1:] -%}
{%- endif -%}

{#- Append tool definitions to system prompt -#}
{%- if tools -%}
    {%- set ns.system_prompt = ns.system_prompt + ("\n" if ns.system_prompt else "") + "List of tools: [" -%}
    {%- for tool in tools -%}
        {%- if tool is not string -%}
            {%- set tool = tool | tojson -%}
        {%- endif -%}
        {%- set ns.system_prompt = ns.system_prompt + tool -%}
        {%- if not loop.last -%}
            {%- set ns.system_prompt = ns.system_prompt + ", " -%}
        {%- endif -%}
    {%- endfor -%}
    {%- set ns.system_prompt = ns.system_prompt + "]" -%}
{%- endif -%}

{%- if ns.system_prompt -%}
    {{- "<|im_start|>system\n" + ns.system_prompt + "<|im_end|>\n" -}}
{%- endif -%}

{#- Find last assistant index for think-stripping logic -#}
{%- set ns.last_assistant_index = -1 -%}
{%- for message in messages -%}
    {%- if message["role"] == "assistant" -%}
        {%- set ns.last_assistant_index = loop.index0 -%}
    {%- endif -%}
{%- endfor -%}

{#- Macro: format a Python value in the style LFM was trained on -#}
{#- Strings → double quotes (via tojson), bools → True/False, None → None -#}
{%- macro pyval(v) -%}
    {%- if v is none -%}None
    {%- elif v is boolean and v -%}True
    {%- elif v is boolean and not v -%}False
    {%- elif v is string -%}{{ v | tojson }}
    {%- elif v is mapping -%}{
        {%- for mk, mv in v.items() -%}
            {{ mk | tojson }}: {{ pyval(mv) }}
            {%- if not loop.last -%}, {% endif -%}
        {%- endfor -%}}
    {%- elif v is iterable -%}[
        {%- for item in v -%}
            {{ pyval(item) }}
            {%- if not loop.last -%}, {% endif -%}
        {%- endfor -%}]
    {%- else -%}{{ v }}
    {%- endif -%}
{%- endmacro -%}

{#- Render each message -#}
{%- for message in messages -%}
    {{- "<|im_start|>" + message["role"] + "\n" -}}

    {%- if message["role"] == "assistant" -%}
        {#- --- ASSISTANT MESSAGE --- -#}

        {#- Get text content, treating None as empty -#}
        {%- set text_content = message["content"] if "content" in message and message["content"] is string else "" -%}

        {#- Reconstruct tool_calls into native format if present -#}
        {%- set tc = message.get("tool_calls", none) if message.get is defined else message["tool_calls"] if "tool_calls" in message else none -%}
        {%- if tc -%}
            {%- set ns.tc_parts = [] -%}
            {%- for call in tc -%}
                {%- if call is mapping -%}
                    {%- set func = call["function"] -%}
                {%- else -%}
                    {%- set func = call.function -%}
                {%- endif -%}
                {%- if func is mapping -%}
                    {%- set fname = func["name"] -%}
                    {%- set fargs = func.get("arguments", {}) if func.get is defined else func["arguments"] if "arguments" in func else {} -%}
                {%- else -%}
                    {%- set fname = func.name -%}
                    {%- set fargs = func.arguments if func.arguments is defined else {} -%}
                {%- endif -%}

                {#- Arguments can be a dict (pre-parsed) or a JSON string (wire format) -#}
                {%- if fargs is mapping -%}
                    {#- Dict: format as pythonic key=value pairs -#}
                    {%- set ns.kv_parts = [] -%}
                    {%- for k, v in fargs.items() -%}
                        {%- set ns.kv_parts = ns.kv_parts + [k + "=" + pyval(v)] -%}
                    {%- endfor -%}
                    {%- set ns.tc_parts = ns.tc_parts + [fname + "(" + ns.kv_parts | join(", ") + ")"] -%}
                {%- elif fargs is string -%}
                    {#- JSON string: embed as-is (no from_json in standard Jinja2) -#}
                    {%- set ns.tc_parts = ns.tc_parts + [fname + "(" + fargs + ")"] -%}
                {%- else -%}
                    {%- set ns.tc_parts = ns.tc_parts + [fname + "()"] -%}
                {%- endif -%}
            {%- endfor -%}
            {%- set tool_call_str = "<|tool_call_start|>[" + ns.tc_parts | join(", ") + "]<|tool_call_end|>" -%}
        {%- else -%}
            {%- set tool_call_str = "" -%}
        {%- endif -%}

        {#- Combine: text content BEFORE tool call markers -#}
        {#- This ordering is safe for think-stripping: -#}
        {#-   <think>...</think>text<|tool_call_start|>...<|tool_call_end|> -#}
        {#-   split("</think>")[-1] → text + markers preserved -#}
        {%- if text_content and tool_call_str -%}
            {%- set content = text_content + tool_call_str -%}
        {%- elif tool_call_str -%}
            {%- set content = tool_call_str -%}
        {%- else -%}
            {%- set content = text_content -%}
        {%- endif -%}

        {#- Strip thinking from non-final assistant messages -#}
        {%- if not keep_past_thinking and loop.index0 != ns.last_assistant_index -%}
            {%- if "</think>" in content -%}
                {%- set content = content.split("</think>")[-1] | trim -%}
            {%- endif -%}
        {%- endif -%}

        {{- content -}}

    {%- elif message["role"] == "tool" -%}
        {#- --- TOOL RESULT MESSAGE --- -#}
        {#- Handle content=None gracefully (render empty instead of "null") -#}
        {%- set content = message["content"] if "content" in message else "" -%}
        {%- if content is none -%}
            {%- set content = "" -%}
        {%- endif -%}
        {%- if content is not string -%}
            {%- set content = content | tojson -%}
        {%- endif -%}
        {{- content -}}

    {%- else -%}
        {#- --- USER / SYSTEM / OTHER MESSAGES --- -#}
        {%- set content = message["content"] -%}
        {%- if content is not string -%}
            {%- set content = content | tojson -%}
        {%- endif -%}
        {{- content -}}

    {%- endif -%}

    {{- "<|im_end|>\n" -}}
{%- endfor -%}

{%- if add_generation_prompt -%}
    {{- "<|im_start|>assistant\n" -}}
{%- endif -%}