[Frontend] Remove confusing -O.xx flag error (#30169)

Signed-off-by: Yanan Cao <gmagogsfm@gmail.com>

tests/utils_/test_argparse_utils.py

@@ -458,22 +458,3 @@ def test_flat_product():
         (3, 4, "a", 5, 6),
         (3, 4, "b", 5, 6),
     ]
-
-
-def test_o_dotted_syntax_error():
-    """Test that -O.* dotted syntax raises a clear error message."""
-    parser = FlexibleArgumentParser()
-    parser.add_argument("-cc", "--compilation-config", type=json.loads)
-
-    # Test that -O.* syntax raises a clear ValueError
-    with pytest.raises(ValueError, match=r"The -O\.\* syntax is no longer supported"):
-        parser.parse_args(["-O.backend=eager"])
-
-    with pytest.raises(ValueError, match=r"Please use -cc\.\* instead"):
-        parser.parse_args(["-O.mode=2"])
-
-    with pytest.raises(
-        ValueError,
-        match=r"replace '-O\.cudagraph_mode=NONE' with '-cc\.cudagraph_mode=NONE'",
-    ):
-        parser.parse_args(["-O.cudagraph_mode=NONE"])

vllm/utils/argparse_utils.py

@@ -244,13 +244,6 @@ class FlexibleArgumentParser(ArgumentParser):
                 else:
                     key = pattern.sub(repl, arg, count=1)
                     processed_args.append(key)
-            elif arg.startswith("-O."):
-                # Provide clear error for deprecated -O.* syntax
-                raise ValueError(
-                    f"The -O.* syntax is no longer supported. "
-                    f"Please use -cc.* instead. "
-                    f"For example, replace '{arg}' with '{arg.replace('-O', '-cc', 1)}'"
-                )
             elif arg.startswith("-O") and arg != "-O":
                 # allow -O flag to be used without space, e.g. -O3 or -Odecode
                 # also handle -O=<optimization_level> here