[Bugfix] Fix gemma4_utils._parse_tool_arguments truncating strings with internal quotes

[Rih0z]

Purpose

Fix vllm/tool_parsers/gemma4_utils._parse_tool_arguments() silently truncating string values that contain " (double quotes). This breaks offline inference tool call parsing for any tool that passes structured text (HTML, code, JSON) as parameters.

This is not duplicating an existing PR. Checked: #38992 (streaming fix only), #39027 (chat template/reasoning, does not touch gemma4_utils.py), #38909 (streaming HTML duplication). No existing PR modifies _parse_tool_arguments.

Fixes #39069

The Bug

_parse_tool_arguments() replaces <|"|> delimiters with ", then uses regex [^"]* which stops at the first internal quote:

# Before: content:<|"|>She said "hello" loudly<|"|>
# After replace: content:"She said "hello" loudly"
# Regex [^"]* captures: "She said " → TRUNCATED

Measured output: {'content': 'She said '} instead of {'content': 'She said "hello" loudly'}

The Fix

The API server parser (gemma4_tool_parser.py) already has a correct implementation (_parse_gemma4_args) that handles <|"|> delimiters natively without replacement. This PR:

1. Moves _parse_gemma4_args, _parse_gemma4_array, _parse_gemma4_value from gemma4_tool_parser.py into gemma4_utils.py as public functions (parse_gemma4_args, etc.)
2. Updates gemma4_tool_parser.py to import from gemma4_utils.py (no behavior change for API server path)
3. Replaces the broken _parse_tool_arguments with a wrapper around parse_gemma4_args (backward compatible — still returns dict[str, str])
4. Adds tests/tool_parsers/test_gemma4_utils.py with regression tests for internal quotes, HTML attributes, braces, and code content
5. Adds test cases to existing test_gemma4_tool_parser.py for the same edge cases

Test commands run and results

# Direct function verification (vLLM not installed — pure Python test):
python -c "... _parse_tool_arguments('content:<|"|>She said \"hello\" loudly<|"|>') ..."
# Result: {'content': 'She said "hello" loudly'} ✅ (was: {'content': 'She said '})

python -c "... _parse_tool_arguments('path:<|"|>out.html<|"|>,content:<|"|><div class=\"main\">hello</div><|"|>') ..."  
# Result: {'path': 'out.html', 'content': '<div class="main">hello</div>'} ✅ (was: {'content': '<div class='})

All 8 manual tests passed (internal quotes, HTML attributes, braces, code, simple string, multi-value, empty, bare numeric).

AI Assistance Disclosure

AI assistance (Claude) was used for code analysis, identifying the root cause, writing tests, and drafting this PR. All changes were reviewed and verified by a human.

🤖 Generated with Claude Code

Co-authored-by: Claude Opus 4.6 (1M context) noreply@anthropic.com

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[gemini-code-assist]

Code Review

This pull request refactors the Gemma4 tool argument parsing by moving core logic to a shared utility module and enhancing the handling of special characters within delimited strings. It also adds comprehensive unit and regression tests. A bug was identified in the nested array parsing logic where the failure to skip string delimiters could lead to incorrect depth calculation when strings contain brackets.

[gemini-code-assist]

The nested array parsing logic is missing the string delimiter skipping logic. If a nested array contains a string with [ or ] characters (e.g., items: [ [<|"|>foo]<|"|> ]), the parser will incorrectly increment or decrement the depth counter and terminate early, leading to truncated or malformed results. This should be consistent with the logic used for nested objects and top-level arrays.

Suggested change

	while i < n and depth > 0:
	if arr_str[i] == "[":
	depth += 1
	elif arr_str[i] == "]":
	depth -= 1
	i += 1
	while i < n and depth > 0:
	if arr_str[i:].startswith(_ESCAPE_TOKEN):
	i += len(_ESCAPE_TOKEN)
	nd = arr_str.find(_ESCAPE_TOKEN, i)
	i = nd + len(_ESCAPE_TOKEN) if nd != -1 else n
	continue
	if arr_str[i] == "[":
	depth += 1
	elif arr_str[i] == "]":
	depth -= 1
	i += 1

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @Rih0z.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork