config: make _config_source_hint type safe

Set to `None` instead of using `hasattr`.

Author: bluetech

src/_pytest/config/__init__.py

@@ -1306,13 +1306,13 @@ def _unconfigure_python_path(self) -> None:
 
     def _validate_args(self, args: list[str], via: str) -> list[str]:
         """Validate known args."""
-        self._parser._config_source_hint = via  # type: ignore
+        self._parser._config_source_hint = via
         try:
             self._parser.parse_known_and_unknown_args(
                 args, namespace=copy.copy(self.option)
             )
         finally:
-            del self._parser._config_source_hint  # type: ignore
+            self._parser._config_source_hint = None
 
         return args
 

src/_pytest/config/argparsing.py

@@ -54,6 +54,7 @@ def __init__(
         # Maps alias -> canonical name.
         self._ini_aliases: dict[str, str] = {}
         self.extra_info: dict[str, Any] = {}
+        self._config_source_hint: str | None = None
 
     def processoption(self, option: Argument) -> None:
         if self._processopt:
@@ -460,7 +461,7 @@ def error(self, message: str) -> NoReturn:
         """Transform argparse error message into UsageError."""
         msg = f"{self.prog}: error: {message}"
 
-        if hasattr(self._parser, "_config_source_hint"):
+        if self._parser._config_source_hint is not None:
             msg = f"{msg} ({self._parser._config_source_hint})"
 
         raise UsageError(self.format_usage() + msg)