feat: Support multiple chat templates - step 1 (#1396)

* Support multiple chat templates - step 1

As a first step, allow user to to select template from metadata with chat_format parameter in the form of `chat_template.name`.

* register chat templates to self.chat_formats instead of globally

* Don't expose internal chat handlers yet

---------

Co-authored-by: Andrei <abetlen@gmail.com>

llama_cpp/llama.py

@@ -378,6 +378,7 @@ class Llama:
 
         self.chat_format = chat_format
         self.chat_handler = chat_handler
+        self._chat_handlers: Dict[str, llama_chat_format.LlamaChatCompletionHandler] = {}
 
         self.draft_model = draft_model
 
@@ -409,10 +410,33 @@ class Llama:
         if self.verbose:
             print(f"Model metadata: {self.metadata}", file=sys.stderr)
 
+        eos_token_id = int(self.metadata.get("tokenizer.ggml.eos_token_id", self.token_eos()))
+        bos_token_id = int(self.metadata.get("tokenizer.ggml.bos_token_id", self.token_bos()))
+
+        eos_token = self._model.token_get_text(eos_token_id)
+        bos_token = self._model.token_get_text(bos_token_id)
+
+        # Unfortunately the llama.cpp API does not return metadata arrays, so we can't get template names from tokenizer.chat_templates
+        template_choices = dict((name[10:], template) for name, template in self.metadata.items() if name.startswith("tokenizer.chat_template."))
+
+        if "tokenizer.chat_template" in self.metadata:
+            template_choices["chat_template.default"] = self.metadata["tokenizer.chat_template"]
+
+        if self.verbose and template_choices:
+            print(f"Available chat formats from metadata: {', '.join(template_choices.keys())}", file=sys.stderr)
+
+        for name, template in template_choices.items():
+            self._chat_handlers[name] = llama_chat_format.Jinja2ChatFormatter(
+                template=template,
+                eos_token=eos_token,
+                bos_token=bos_token,
+                stop_token_ids=[eos_token_id],
+            ).to_chat_handler()
+
         if (
             self.chat_format is None
             and self.chat_handler is None
-            and "tokenizer.chat_template" in self.metadata
+            and "chat_template.default" in template_choices
         ):
             chat_format = llama_chat_format.guess_chat_format_from_gguf_metadata(
                 self.metadata
@@ -423,30 +447,12 @@ class Llama:
                 if self.verbose:
                     print(f"Guessed chat format: {chat_format}", file=sys.stderr)
             else:
-                template = self.metadata["tokenizer.chat_template"]
-                try:
-                    eos_token_id = int(self.metadata["tokenizer.ggml.eos_token_id"])
-                except:
-                    eos_token_id = self.token_eos()
-                try:
-                    bos_token_id = int(self.metadata["tokenizer.ggml.bos_token_id"])
-                except:
-                    bos_token_id = self.token_bos()
-
-                eos_token = self._model.token_get_text(eos_token_id)
-                bos_token = self._model.token_get_text(bos_token_id)
-
                 if self.verbose:
-                    print(f"Using gguf chat template: {template}", file=sys.stderr)
+                    print(f"Using gguf chat template: {template_choices['chat_template.default']}", file=sys.stderr)
                     print(f"Using chat eos_token: {eos_token}", file=sys.stderr)
                     print(f"Using chat bos_token: {bos_token}", file=sys.stderr)
 
-                self.chat_handler = llama_chat_format.Jinja2ChatFormatter(
+                self.chat_format = "chat_template.default"
-                    template=template,
-                    eos_token=eos_token,
-                    bos_token=bos_token,
-                    stop_token_ids=[eos_token_id],
-                ).to_chat_handler()
 
         if self.chat_format is None and self.chat_handler is None:
             self.chat_format = "llama-2"
@@ -1719,7 +1725,7 @@ class Llama:
         Returns:
             Generated chat completion or a stream of chat completion chunks.
         """
-        handler = self.chat_handler or llama_chat_format.get_chat_completion_handler(
+        handler = self.chat_handler or self._chat_handlers.get(self.chat_format) or llama_chat_format.get_chat_completion_handler(
             self.chat_format
         )
         return handler(