What are the rules to create a chatPromptTemplate in .env.local?

[houghtonweihu]

We know that chatPromptTemplate for google/gemma-7b-it in .env.local is:

"chatPromptTemplate" : "{{#each messages}}{{#ifUser}}<start_of_turn>user\n{{#if @FIRST}}{{#if @root.preprompt}}{{@root.preprompt}}\n{{/if}}{{/if}}{{content}}<end_of_turn>\n<start_of_turn>model\n{{/ifUser}}{{#ifAssistant}}{{content}}<end_of_turn>\n{{/ifAssistant}}{{/each}}",

and its chat template is:
"chat_template": "{{ bos_token }}{% if messages[0]['role'] == 'system' %}{{ raise_exception('System role not supported') }}{% endif %}{% for message in messages %}{% if (message['role'] == 'user') != (loop.index0 % 2 == 0) %}{{ raise_exception('Conversation roles must alternate user/assistant/user/assistant/...') }}{% endif %}{% if (message['role'] == 'assistant') %}{% set role = 'model' %}{% else %}{% set role = message['role'] %}{% endif %}{{ '<start_of_turn>' + role + '\n' + message['content'] | trim + '<end_of_turn>\n' }}{% endfor %}{% if add_generation_prompt %}{{'<start_of_turn>model\n'}}{% endif %}",

The question is:
Are there any rules that are used to create the chatPromptTemplate for a model? Usually we have
the chat template from the model. But when we need to use this model in chat-ui, we have to use chatPromptTemplate.

[nsarrazin]

We settled on using handlebars for chat templates within chat-ui as the chat templates you refer to use jinja, which didn't have a satisfying JS implementation at the time.

Now we have better support for jinja and this PR adds support for using chat templates directly. It's still in draft stage but feel free to let us know if this would be useful to you!

In the meantime here's a list of some prompt template examples: https://github.com/huggingface/chat-ui/blob/main/PROMPTS.md which should help you get started in writing your own.

[philippgille]

There are some things I don't understand about the templates. For example the OpenChat template:

1. Why does the OpenChat template start with <s> but doesn't have any </s> to end the tag? Is there documentation on what <s> is?
2. Why does it reference {{@root.preprompt}}, while others reference just {{preprompt}}? Where is each one from?