Fold remaining custom stdlib *Buffer types into _typeshed. (#6082)

Add ctypes base type to WriteableBuffer.
Add a ReadOnlyBuffer type from fcntl.
Base ReadableBuffer on WriteableBuffer and ReadOnlyBuffer.
Use these types in fcntl and ctypes stubs.

stdlib/_typeshed/__init__.pyi

@@ -3,6 +3,7 @@
 # See the README.md file in this directory for more information.
 
 import array
+import ctypes
 import mmap
 import sys
 from os import PathLike
@@ -167,8 +168,13 @@ class SupportsNoArgReadline(Protocol[_T_co]):
 class SupportsWrite(Protocol[_T_contra]):
     def write(self, __s: _T_contra) -> Any: ...
 
-ReadableBuffer = Union[bytes, bytearray, memoryview, array.array[Any], mmap.mmap]  # stable
-WriteableBuffer = Union[bytearray, memoryview, array.array[Any], mmap.mmap]  # stable
+ReadOnlyBuffer = bytes  # stable
+# Anything that implements the read-write buffer interface.
+# The buffer interface is defined purely on the C level, so we cannot define a normal Protocol
+# for it. Instead we have to list the most common stdlib buffer classes in a Union.
+WriteableBuffer = Union[bytearray, memoryview, array.array[Any], mmap.mmap, ctypes._CData]  # stable
+# Same as _WriteableBuffer, but also includes read-only buffer types (like bytes).
+ReadableBuffer = Union[ReadOnlyBuffer, WriteableBuffer]  # stable
 
 # stable
 if sys.version_info >= (3, 10):

stdlib/ctypes/__init__.pyi

@@ -1,5 +1,5 @@
 import sys
-from array import array
+from _typeshed import ReadableBuffer, WriteableBuffer
 from typing import (
     Any,
     Callable,
@@ -72,13 +72,6 @@ if sys.platform == "win32":
 pydll: LibraryLoader[PyDLL]
 pythonapi: PyDLL
 
-# Anything that implements the read-write buffer interface.
-# The buffer interface is defined purely on the C level, so we cannot define a normal Protocol
-# for it. Instead we have to list the most common stdlib buffer classes in a Union.
-_WritableBuffer = _UnionT[bytearray, memoryview, array[Any], _CData]
-# Same as _WritableBuffer, but also includes read-only buffer types (like bytes).
-_ReadOnlyBuffer = _UnionT[_WritableBuffer, bytes]
-
 class _CDataMeta(type):
     # By default mypy complains about the following two methods, because strictly speaking cls
     # might not be a Type[_CT]. However this can never actually happen, because the only class that
@@ -91,9 +84,9 @@ class _CData(metaclass=_CDataMeta):
     _b_needsfree_: bool
     _objects: Mapping[Any, int] | None
     @classmethod
-    def from_buffer(cls: Type[_CT], source: _WritableBuffer, offset: int = ...) -> _CT: ...
+    def from_buffer(cls: Type[_CT], source: WriteableBuffer, offset: int = ...) -> _CT: ...
     @classmethod
-    def from_buffer_copy(cls: Type[_CT], source: _ReadOnlyBuffer, offset: int = ...) -> _CT: ...
+    def from_buffer_copy(cls: Type[_CT], source: ReadableBuffer, offset: int = ...) -> _CT: ...
     @classmethod
     def from_address(cls: Type[_CT], address: int) -> _CT: ...
     @classmethod

stdlib/fcntl.pyi

@@ -1,7 +1,6 @@
 import sys
-from _typeshed import FileDescriptorLike
-from array import array
-from typing import Any, Union, overload
+from _typeshed import FileDescriptorLike, ReadOnlyBuffer, WriteableBuffer
+from typing import Any, overload
 from typing_extensions import Literal
 
 FASYNC: int
@@ -85,17 +84,13 @@ LOCK_WRITE: int
 def fcntl(__fd: FileDescriptorLike, __cmd: int, __arg: int = ...) -> int: ...
 @overload
 def fcntl(__fd: FileDescriptorLike, __cmd: int, __arg: bytes) -> bytes: ...
-
-_ReadOnlyBuffer = bytes
-_WritableBuffer = Union[bytearray, memoryview, array[Any]]
-
 @overload
 def ioctl(__fd: FileDescriptorLike, __request: int, __arg: int = ..., __mutate_flag: bool = ...) -> int: ...
 @overload
-def ioctl(__fd: FileDescriptorLike, __request: int, __arg: _WritableBuffer, __mutate_flag: Literal[True] = ...) -> int: ...
+def ioctl(__fd: FileDescriptorLike, __request: int, __arg: WriteableBuffer, __mutate_flag: Literal[True] = ...) -> int: ...
 @overload
-def ioctl(__fd: FileDescriptorLike, __request: int, __arg: _WritableBuffer, __mutate_flag: Literal[False]) -> bytes: ...
+def ioctl(__fd: FileDescriptorLike, __request: int, __arg: WriteableBuffer, __mutate_flag: Literal[False]) -> bytes: ...
 @overload
-def ioctl(__fd: FileDescriptorLike, __request: int, __arg: _ReadOnlyBuffer, __mutate_flag: bool = ...) -> bytes: ...
+def ioctl(__fd: FileDescriptorLike, __request: int, __arg: ReadOnlyBuffer, __mutate_flag: bool = ...) -> bytes: ...
 def flock(__fd: FileDescriptorLike, __operation: int) -> None: ...
 def lockf(__fd: FileDescriptorLike, __cmd: int, __len: int = ..., __start: int = ..., __whence: int = ...) -> Any: ...