Use SupportsWrite protocol from typeshed (#18404)

mypy/main.py

@@ -11,7 +11,7 @@
 from collections.abc import Sequence
 from gettext import gettext
 from io import TextIOWrapper
-from typing import IO, Any, Final, NoReturn, Protocol, TextIO
+from typing import IO, TYPE_CHECKING, Any, Final, NoReturn, TextIO
 
 from mypy import build, defaults, state, util
 from mypy.config_parser import (
@@ -36,9 +36,8 @@
 from mypy.split_namespace import SplitNamespace
 from mypy.version import __version__
 
-
-class _SupportsWrite(Protocol):
-    def write(self, s: str, /) -> object: ...
+if TYPE_CHECKING:
+    from _typeshed import SupportsWrite
 
 
 orig_stat: Final = os.stat
@@ -378,17 +377,17 @@ def __init__(self, *args: Any, **kwargs: Any) -> None:
     # =====================
     # Help-printing methods
     # =====================
-    def print_usage(self, file: _SupportsWrite | None = None) -> None:
+    def print_usage(self, file: SupportsWrite[str] | None = None) -> None:
         if file is None:
             file = self.stdout
         self._print_message(self.format_usage(), file)
 
-    def print_help(self, file: _SupportsWrite | None = None) -> None:
+    def print_help(self, file: SupportsWrite[str] | None = None) -> None:
         if file is None:
             file = self.stdout
         self._print_message(self.format_help(), file)
 
-    def _print_message(self, message: str, file: _SupportsWrite | None = None) -> None:
+    def _print_message(self, message: str, file: SupportsWrite[str] | None = None) -> None:
         if message:
             if file is None:
                 file = self.stderr