Olmo3 tool parser and tests

[pdasigi]

Purpose

This PR adds a tool parser for parsing the function calls made by the Olmo 3 model. Support for the model has already been merged (#24534). Olmo 3 outputs function calls in the following format

<function_calls>function1(arg1=value1)\nfunction2(arg2=value2)</function_calls>

This format is similar to the one that the existing Pythonic parser expects except for the presence of xml tags and function calls being delimited by newline characters instead of being represented as a list within brackets.

Test Plan

This PR also includes tests. Existing tests have not been modified or will be impacted.

Test Result

pytest tests/entrypoints/openai/tool_parsers/test_olmo3_tool_parser.py

Output:

========================================================================= test session starts ==========================================================================
platform darwin -- Python 3.11.13, pytest-8.4.2, pluggy-1.6.0
rootdir: /Users/pradeepd/workspace/vllm
configfile: pyproject.toml
plugins: anyio-4.10.0
collected 20 items                                                                                                                                                     

tests/entrypoints/openai/tool_parsers/test_olmo3_tool_parser.py ....................                                                                             [100%]

========================================================================== 20 passed in 1.67s ==========================================================================

---

Essential Elements of an Effective PR Description Checklist

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
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• (Optional) Release notes update. If your change is user facing, please update the release notes draft in the Google Doc.

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[gemini-code-assist]

Code Review

This pull request introduces a tool parser for the Olmo 3 model, which uses a Pythonic function call format wrapped in XML-like tags. The implementation is accompanied by a comprehensive set of tests. My review focuses on the correctness and maintainability of the new parser. I've identified a few issues related to how the XML tags are removed, which could lead to incorrect parsing of tool calls. Additionally, there's significant code duplication from an existing parser, which could pose future maintenance challenges. I've provided suggestions to address these points.

[gemini-code-assist]

This class duplicates a significant amount of code from PythonicToolParser. This creates a maintenance burden, as changes in one parser may need to be manually synchronized with the other. To improve maintainability, consider refactoring to share code. One approach is to have Olmo3PythonicToolParser inherit from PythonicToolParser and override specific methods. The differences in helper functions like _get_parameter_value could be handled by making them methods of the class, allowing them to be overridden as well.

[gemini-code-assist]

Using str.replace() to remove the <function_calls> tags is not safe. If the tag strings appear inside a function argument (e.g., as part of a string literal), replace() will incorrectly remove them, corrupting the tool call data. It's safer to use a regular expression to extract only the content between the outermost tags.

Suggested change

	# Remove xml tags.
	model_output = (
	model_output.replace("<function_calls>", "").replace("</function_calls>", "").strip()
	)
	# Extract content from within <function_calls> tags.
	match = re.search(r"<function_calls>(.*?)</function_calls>",
	model_output, re.DOTALL)
	if match:
	model_output = match.group(1).strip()

[gemini-code-assist]

Using rfind to remove the closing </function_calls> tag is unsafe. If the tag string appears within a function's string argument, rfind could find the wrong occurrence and truncate the text incorrectly. Since this is for streaming and the closing tag is expected at the very end of the complete tool call block, you can safely remove it by slicing from the end of the string.

            if current_text.endswith("</function_calls>"):
                current_text = current_text[:-len("</function_calls>")]