From b4f4c5e01374945b5ed87db123ea522cdf58b2a7 Mon Sep 17 00:00:00 2001
From: Ben Browning <bbrownin@redhat.com>
Date: Thu, 18 Jun 2026 11:04:02 +0000
Subject: [PATCH] [Bugfix] [Parser] Fix Qwen3 partial param regex dropping
 values containing <

_PARTIAL_PARAM_RE used [^<]*$ to capture in-progress parameter content.
When a value contained a literal < (HTML, code, math like x<5), the
regex failed to match entirely, silently dropping the parameter during
streaming.

Fix by changing [^<]*$ to (.*)$ so the capture group accepts any
character including <.

Co-Authored-By: Claude <noreply@anthropic.com>

Signed-off-by: Ben Browning <bbrownin@redhat.com>
---
 tests/parser/engine/test_qwen3.py | 18 ++++++++++++++++++
 vllm/parser/qwen3.py              |  2 +-
 2 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/tests/parser/engine/test_qwen3.py b/tests/parser/engine/test_qwen3.py
index 7c2255ac7b2b..06784212e1b7 100644
--- a/tests/parser/engine/test_qwen3.py
+++ b/tests/parser/engine/test_qwen3.py
@@ -615,6 +615,24 @@ def test_partial_multiline(self):
         assert result["command"] == "ls -la"
         assert result["desc"] == "\npartial value"
 
+    def test_partial_value_with_angle_bracket(self):
+        from vllm.parser.qwen3 import (
+            _qwen3_arg_converter,
+        )
+
+        raw = "<parameter=expr>x<5"
+        result = json.loads(_qwen3_arg_converter(raw, partial=True))
+        assert result == {"expr": "x<5"}
+
+    def test_partial_value_with_angle_bracket_and_complete_param(self):
+        from vllm.parser.qwen3 import (
+            _qwen3_arg_converter,
+        )
+
+        raw = "<parameter=city>Tokyo</parameter>\n<parameter=expr>x<5"
+        result = json.loads(_qwen3_arg_converter(raw, partial=True))
+        assert result == {"city": "Tokyo", "expr": "x<5"}
+
 
 class TestSchemaAwareTypeCoercion:
     """Verify that _fix_arg_types corrects miscoerced values using the
diff --git a/vllm/parser/qwen3.py b/vllm/parser/qwen3.py
index ed47b1b9254d..45e3c7e43255 100644
--- a/vllm/parser/qwen3.py
+++ b/vllm/parser/qwen3.py
@@ -49,7 +49,7 @@
     r"(?:<\s*/\s*parameter\s*>|(?=<\s*parameter\s*=))",
     re.DOTALL,
 )
-_PARTIAL_PARAM_RE = re.compile(r"<\s*parameter\s*=\s*([^>]+)>([^<]*)$", re.DOTALL)
+_PARTIAL_PARAM_RE = re.compile(r"<\s*parameter\s*=\s*([^>]+)>(.*)$", re.DOTALL)
 
 
 def _qwen3_arg_converter(raw_args: str, partial: bool) -> str: