[Bugfix] Fix IndexError when choosing tool while having a tool parser

[tjohnson31415]

When running the server supporting auto-tool use but with a streaming request that specifies the function to call, the [DONE] message does not get sent and there is an exception raised.

See #9048 for details on a repro case.

From what I see, the code is using the existence of tool_parser to indicate that it is being used for auto-tool choice, but it is valid to send a request without auto tools selection but with the server configured to support it. So the change here is to explicilty check for tool_choice_auto being true when using the tool_parser.

FIX #9048

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[maxdebayser]

@tjohnson31415 , I think these changes make sense, but this PR also fixed the error: #8709 . I can't reproduce the problem with the latest main anymore. If I apply this diff to the version I think you're using, the problem doesn't happen anymore:

@@ -285,12 +285,8 @@
         num_choices = 1 if request.n is None else request.n
         previous_num_tokens = [0] * num_choices
         finish_reason_sent = [False] * num_choices
-
         num_prompt_tokens = 0
 
-        tool_parser: Optional[ToolParser] = self.tool_parser(
-            tokenizer) if self.tool_parser else None
-
         if isinstance(request.tool_choice, ChatCompletionNamedToolChoiceParam):
             tool_choice_function_name = request.tool_choice.function.name
         else:
@@ -309,6 +305,21 @@
         else:
             previous_texts, all_previous_token_ids = None, None
 
+        # Prepare the tool parser if it's needed
+        try:
+            if tool_choice_auto and self.tool_parser:
+                tool_parsers: List[Optional[ToolParser]] = [
+                    self.tool_parser(tokenizer)
+                ] * num_choices
+            else:
+                tool_parsers = [None] * num_choices
+        except RuntimeError as e:
+            logger.error("Error in tool parser creation: %s", e)
+            data = self.create_streaming_error_response(str(e))
+            yield f"data: {data}\n\n"
+            yield "data: [DONE]\n\n"
+            return
+
         try:
             async for res in result_generator:
                 if res.prompt_token_ids is not None:
@@ -402,6 +413,7 @@
 
                 for output in res.outputs:
                     i = output.index
+                    tool_parser = tool_parsers[i]
 
                     if finish_reason_sent[i]:
                         continue

[tjohnson31415]

Ah, yep, looks like that fix works too. After that change, the non-None-ness of tool_parser now includes checking auto_tool_choice, so it is effectively the same.

Thanks for taking a look @maxdebayser!