[Bugfix] Fix Llama3JsonToolParser regex to support deeply nested JSON

The previous regex pattern could only handle one level of JSON nesting,
causing it to fail on tool calls with nested parameters like:
{"name": "tool", "parameters": {"location": {"city": "SF", "state": "CA"}}}

This fix replaces the pattern with a recursive regex using (?R) that
supports arbitrary nesting depth while maintaining backward compatibility.

Added regression tests for 2-level and 3+ level nested JSON structures.

Signed-off-by: ym820 <yikai.mao@outlook.com>

Author: ym820

tests/entrypoints/openai/tool_parsers/test_llama3_json_tool_parser.py

@@ -132,3 +132,44 @@ def test_extract_tool_calls_multiple_json_with_surrounding_text(parser):
     assert result.tool_calls[0].function.name == "searchTool"
     assert result.tool_calls[1].function.name == "getOpenIncidentsTool"
     assert result.tool_calls[2].function.name == "searchTool"
+
+
+def test_extract_tool_calls_deeply_nested_json(parser):
+    # Test with deeply nested JSON (more than 2 levels)
+    # This is a regression test for the regex pattern bug
+    model_output = (
+        '{"name": "get_current_conditions", '
+        '"parameters": {"location": {"city": "San Francisco", "state": "CA"}, '
+        '"unit": "Fahrenheit"}}'
+    )
+    result = parser.extract_tool_calls(model_output, None)
+
+    assert result.tools_called is True
+    assert len(result.tool_calls) == 1
+    assert result.tool_calls[0].function.name == "get_current_conditions"
+
+    # Verify the entire parameters object is captured
+    import json
+    args = json.loads(result.tool_calls[0].function.arguments)
+    assert "location" in args
+    assert args["location"]["city"] == "San Francisco"
+    assert args["location"]["state"] == "CA"
+    assert args["unit"] == "Fahrenheit"
+
+
+def test_extract_tool_calls_very_deeply_nested_json(parser):
+    # Test with very deeply nested JSON (3+ levels)
+    model_output = (
+        '{"name": "complex_tool", '
+        '"parameters": {"level1": {"level2": {"level3": {"value": "deep"}}}}}'
+    )
+    result = parser.extract_tool_calls(model_output, None)
+
+    assert result.tools_called is True
+    assert len(result.tool_calls) == 1
+    assert result.tool_calls[0].function.name == "complex_tool"
+
+    # Verify the entire nested structure is captured
+    import json
+    args = json.loads(result.tool_calls[0].function.arguments)
+    assert args["level1"]["level2"]["level3"]["value"] == "deep"

vllm/entrypoints/openai/tool_parsers/llama_tool_parser.py

@@ -57,9 +57,10 @@ def __init__(self, tokenizer: PreTrainedTokenizerBase):
             0
         ]
         # Updated regex to match multiple JSONs separated by semicolons
-        # This pattern is more robust and can handle nested JSON objects
+        # This pattern uses recursion to handle arbitrarily nested JSON objects
+        # (?R) is a recursive pattern that matches the entire pattern again
         self.tool_call_regex = re.compile(
-            r"{[^{}]*(?:{[^{}]*}[^{}]*)*}(?:\s*;\s*{[^{}]*(?:{[^{}]*}[^{}]*)*})*",
+            r"\{(?:[^{}]|(?R))*\}(?:\s*;\s*\{(?:[^{}]|(?R))*\})*",
             re.DOTALL,
         )