Replace a few instances of IO with protocols (#4296)

stdlib/3/imp.pyi

@@ -2,7 +2,7 @@ import os
 import sys
 import types
 from _typeshed import StrPath
-from typing import IO, Any, List, Optional, Tuple, TypeVar, Union
+from typing import IO, Any, List, Optional, Protocol, Tuple, TypeVar, Union
 
 from _imp import (
     acquire_lock as acquire_lock,
@@ -40,12 +40,23 @@ class NullImporter:
     def __init__(self, path: StrPath) -> None: ...
     def find_module(self, fullname: Any) -> None: ...
 
-# PathLike doesn't work for the pathname argument here
-def load_source(name: str, pathname: str, file: Optional[IO[Any]] = ...) -> types.ModuleType: ...
-def load_compiled(name: str, pathname: str, file: Optional[IO[Any]] = ...) -> types.ModuleType: ...
-def load_package(name: str, path: StrPath) -> types.ModuleType: ...
-def load_module(name: str, file: IO[Any], filename: str, details: Tuple[str, str, int]) -> types.ModuleType: ...
+# Technically, a text file has to support a slightly different set of operations than a binary file,
+# but we ignore that here.
+class _FileLike(Protocol):
+    closed: bool
+    mode: str
+    def read(self) -> Union[str, bytes]: ...
+    def close(self) -> Any: ...
+    def __enter__(self) -> Any: ...
+    def __exit__(self, *args: Any) -> Any: ...
 
+# PathLike doesn't work for the pathname argument here
+def load_source(name: str, pathname: str, file: Optional[_FileLike] = ...) -> types.ModuleType: ...
+def load_compiled(name: str, pathname: str, file: Optional[_FileLike] = ...) -> types.ModuleType: ...
+def load_package(name: str, path: StrPath) -> types.ModuleType: ...
+def load_module(name: str, file: Optional[_FileLike], filename: str, details: Tuple[str, str, int]) -> types.ModuleType: ...
+
+# IO[Any] is a TextIOWrapper if name is a .py file, and a FileIO otherwise.
 if sys.version_info >= (3, 6):
     def find_module(
         name: str, path: Union[None, List[str], List[os.PathLike[str]], List[StrPath]] = ...
@@ -56,4 +67,4 @@ else:
 
 def reload(module: types.ModuleType) -> types.ModuleType: ...
 def init_builtin(name: str) -> Optional[types.ModuleType]: ...
-def load_dynamic(name: str, path: str, file: Optional[IO[Any]] = ...) -> types.ModuleType: ...
+def load_dynamic(name: str, path: str, file: Any = ...) -> types.ModuleType: ...  # file argument is ignored