fix: normalize malformed <parameter> tags (Qwen3) (#10539)

openhands/llm/fn_call_converter.py

@@ -705,6 +705,25 @@ def _fix_stopword(content: str) -> str:
     return content
 
 
+def _normalize_parameter_tags(fn_body: str) -> str:
+    """Normalize malformed parameter tags to the canonical format.
+
+    Some models occasionally emit malformed parameter tags like:
+        <parameter=command=str_replace</parameter>
+    instead of the correct:
+        <parameter=command>str_replace</parameter>
+
+    This function rewrites the malformed form into the correct one to allow
+    downstream parsing to succeed.
+    """
+    # Replace '<parameter=name=value</parameter>' with '<parameter=name>value</parameter>'
+    return re.sub(
+        r'<parameter=([a-zA-Z0-9_]+)=([^<]*)</parameter>',
+        r'<parameter=\1>\2</parameter>',
+        fn_body,
+    )
+
+
 def convert_non_fncall_messages_to_fncall_messages(
     messages: list[dict],
     tools: list[ChatCompletionToolParam],
@@ -852,7 +871,7 @@ def convert_non_fncall_messages_to_fncall_messages(
 
             if fn_match:
                 fn_name = fn_match.group(1)
-                fn_body = fn_match.group(2)
+                fn_body = _normalize_parameter_tags(fn_match.group(2))
                 matching_tool = next(
                     (
                         tool['function']

tests/unit/llm/test_llm_fncall_converter.py

@@ -96,6 +96,52 @@ FNCALL_TOOLS: list[ChatCompletionToolParam] = [
 ]
 
 
+def test_malformed_parameter_parsing_recovery():
+    """Ensure we can recover when models emit malformed parameter tags like <parameter=command=str_replace</parameter>.
+
+    This simulates a tool call to str_replace_editor where the 'command' parameter is malformed.
+    """
+    from openhands.llm.fn_call_converter import (
+        convert_non_fncall_messages_to_fncall_messages,
+    )
+
+    # Construct an assistant message with malformed parameter tag for 'command'
+    assistant_message = {
+        'role': 'assistant',
+        'content': (
+            '<function=str_replace_editor>\n'
+            '<parameter=command=str_replace</parameter>\n'  # malformed form
+            '<parameter=path>/repo/app.py</parameter>\n'
+            '<parameter=old_str>foo</parameter>\n'
+            '<parameter=new_str>bar</parameter>\n'
+            '</function>'
+        ),
+    }
+
+    messages = [
+        {'role': 'system', 'content': 'test'},
+        {'role': 'user', 'content': 'do edit'},
+        assistant_message,
+    ]
+
+    converted = convert_non_fncall_messages_to_fncall_messages(messages, FNCALL_TOOLS)
+
+    # The last message should be assistant with a parsed tool call
+    last = converted[-1]
+    assert last['role'] == 'assistant'
+    assert 'tool_calls' in last and len(last['tool_calls']) == 1
+    tool_call = last['tool_calls'][0]
+    assert tool_call['type'] == 'function'
+    assert tool_call['function']['name'] == 'str_replace_editor'
+
+    # Arguments must be a valid JSON with command=str_replace and proper params
+    args = json.loads(tool_call['function']['arguments'])
+    assert args['command'] == 'str_replace'
+    assert args['path'] == '/repo/app.py'
+    assert args['old_str'] == 'foo'
+    assert args['new_str'] == 'bar'
+
+
 def test_convert_tools_to_description():
     formatted_tools = convert_tools_to_description(FNCALL_TOOLS)
     print(formatted_tools)