fix: treat `--tool-call-parser` and `--dyn-tool-call-parser` independently for SGLang (#5849)

Signed-off-by: Krishnan Prashanth <kprashanth@nvidia.com>

components/src/dynamo/sglang/args.py

@@ -239,47 +239,13 @@ def _preprocess_for_encode_config(
     }
 
 
-def _set_parser(
-    sglang_str: Optional[str],
-    dynamo_str: Optional[str],
-    arg_name: str = "tool-call-parser",
-) -> Optional[str]:
-    """Resolve parser name from SGLang and Dynamo arguments.
-
-    Args:
-        sglang_str: Parser value from SGLang argument.
-        dynamo_str: Parser value from Dynamo argument.
-        arg_name: Name of the parser argument for logging.
-
-    Returns:
-        Resolved parser name, preferring Dynamo's value if both set.
-
-    Raises:
-        ValueError: If parser name is not valid.
-    """
-    # If both are present, give preference to dynamo_str
-    if sglang_str is not None and dynamo_str is not None:
-        logging.warning(
-            f"--dyn-{arg_name} and --{arg_name} are both set. Giving preference to --dyn-{arg_name}"
-        )
-        return dynamo_str
-    # If dynamo_str is not set, use try to use sglang_str if it matches with the allowed parsers
-    elif sglang_str is not None:
-        logging.warning(f"--dyn-{arg_name} is not set. Using --{arg_name}.")
-        if arg_name == "tool-call-parser" and sglang_str not in get_tool_parser_names():
-            raise ValueError(
-                f"--{arg_name} is not a valid tool call parser. Valid parsers are: {get_tool_parser_names()}"
-            )
-        elif (
-            arg_name == "reasoning-parser"
-            and sglang_str not in get_reasoning_parser_names()
-        ):
-            raise ValueError(
-                f"--{arg_name} is not a valid reasoning parser. Valid parsers are: {get_reasoning_parser_names()}"
-            )
-        return sglang_str
-    else:
-        return dynamo_str
+def _validate_parser_flags(
+    sglang_val: Optional[str], dynamo_val: Optional[str], name: str
+) -> None:
+    """Validate that --{name} (SGLang) and --dyn-{name} (Dynamo) are not both set."""
+    if sglang_val and dynamo_val:
+        logging.error(f"Cannot use both --{name} and --dyn-{name}.")
+        sys.exit(1)
 
 
 def _extract_config_section(
@@ -498,16 +464,20 @@ async def parse_args(args: list[str]) -> Config:
 
     parsed_namespace, parsed_component_name, parsed_endpoint_name = endpoint_parts
 
-    tool_call_parser = _set_parser(
+    # Validate parser flags: error if both --{name} and --dyn-{name} are set.
+    # --dyn-{name} choices are validated by argparse; --{name} by SGLang.
+    _validate_parser_flags(
         parsed_args.tool_call_parser,
         parsed_args.dyn_tool_call_parser,
         "tool-call-parser",
     )
-    reasoning_parser = _set_parser(
+    _validate_parser_flags(
         parsed_args.reasoning_parser,
         parsed_args.dyn_reasoning_parser,
         "reasoning-parser",
     )
+    tool_call_parser = parsed_args.dyn_tool_call_parser
+    reasoning_parser = parsed_args.dyn_reasoning_parser
 
     if parsed_args.custom_jinja_template and parsed_args.use_sglang_tokenizer:
         logging.error(

components/src/dynamo/sglang/tests/test_sglang_unit.py

@@ -75,3 +75,48 @@ async def test_custom_jinja_template_env_var_expansion(monkeypatch, mock_sglang_
         f"Expected custom_jinja_template value to be {JINJA_TEMPLATE_PATH}, "
         f"got {config.dynamo_args.custom_jinja_template}"
     )
+
+
+# --- Tool Call Parser Validation Tests ---
+
+
+@pytest.mark.asyncio
+async def test_tool_call_parser_valid_with_dynamo_tokenizer(mock_sglang_cli):
+    """Valid parser name works when using Dynamo's tokenizer."""
+    mock_sglang_cli(
+        "--model",
+        "Qwen/Qwen3-0.6B",
+        "--dyn-tool-call-parser",
+        "hermes",  # supported by Dynamo
+    )
+
+    config = await parse_args(sys.argv[1:])
+
+    assert config.dynamo_args.tool_call_parser == "hermes"
+
+
+@pytest.mark.asyncio
+async def test_tool_call_parser_invalid_with_dynamo_tokenizer(mock_sglang_cli):
+    """Invalid parser name exits when using Dynamo's tokenizer."""
+    mock_sglang_cli(
+        "--model", "Qwen/Qwen3-0.6B", "--dyn-tool-call-parser", "nonexistent_parser"
+    )
+
+    with pytest.raises(SystemExit):
+        await parse_args(sys.argv[1:])
+
+
+@pytest.mark.asyncio
+async def test_tool_call_parser_both_flags_error(mock_sglang_cli):
+    """Setting both --dyn-tool-call-parser and --tool-call-parser exits with error."""
+    mock_sglang_cli(
+        "--model",
+        "Qwen/Qwen3-0.6B",
+        "--dyn-tool-call-parser",
+        "hermes",
+        "--tool-call-parser",
+        "qwen25",
+    )
+
+    with pytest.raises(SystemExit):
+        await parse_args(sys.argv[1:])