Unify file descriptor definitions (#3584)

The _types module can house any common type defintions used throughout
the rest of typeshed to keep defintions in sync.

First candidate is file descriptors where anything with `fileno()`
method is accepted. There were several different implementations in
various files that can be unified.

stdlib/2and3/_types.pyi

@@ -0,0 +1,10 @@
+# These types are for typeshed-only objects that don't exist at runtime
+
+from typing import type_check_only, Protocol, Union
+
+@type_check_only
+class HasFileno(Protocol):
+    def fileno(self) -> int: ...
+
+FileDescriptor = int
+FileDescriptorLike = Union[int, HasFileno]

stdlib/2and3/asyncore.pyi

@@ -7,6 +7,7 @@ import time
 import warnings
 from socket import SocketType
 from typing import Optional
+from _types import FileDescriptorLike
 
 from errno import (EALREADY, EINPROGRESS, EWOULDBLOCK, ECONNRESET, EINVAL,
                    ENOTCONN, ESHUTDOWN, EINTR, EISCONN, EBADF, ECONNABORTED,
@@ -141,5 +142,5 @@ class file_wrapper:
     def fileno(self) -> int: ...
 
 class file_dispatcher(dispatcher):
-    def __init__(self, fd: int, map: _maptype = ...) -> None: ...
+    def __init__(self, fd: FileDescriptorLike, map: _maptype = ...) -> None: ...
     def set_file(self, fd: int) -> None: ...

stdlib/2and3/select.pyi

@@ -1,10 +1,7 @@
 import sys
 from typing import Any, Iterable, List, Optional, Protocol, Tuple, Union
+from _types import FileDescriptorLike
 
-class _HasFileno(Protocol):
-    def fileno(self) -> int: ...
-
-_FileDescriptor = Union[int, _HasFileno]
 
 EPOLLERR: int
 EPOLLET: int
@@ -71,9 +68,9 @@ POLLWRNORM: int
 
 class poll:
     def __init__(self) -> None: ...
-    def register(self, fd: _FileDescriptor, eventmask: int = ...) -> None: ...
-    def modify(self, fd: _FileDescriptor, eventmask: int) -> None: ...
-    def unregister(self, fd: _FileDescriptor) -> None: ...
+    def register(self, fd: FileDescriptorLike, eventmask: int = ...) -> None: ...
+    def modify(self, fd: FileDescriptorLike, eventmask: int) -> None: ...
+    def unregister(self, fd: FileDescriptorLike) -> None: ...
     def poll(self, timeout: Optional[float] = ...) -> List[Tuple[int, int]]: ...
 
 def select(rlist: Iterable[Any], wlist: Iterable[Any], xlist: Iterable[Any],
@@ -94,7 +91,7 @@ class kevent(object):
     flags: int
     ident: int
     udata: Any
-    def __init__(self, ident: _FileDescriptor, filter: int = ..., flags: int = ..., fflags: int = ..., data: Any = ..., udata: Any = ...) -> None: ...
+    def __init__(self, ident: FileDescriptorLike, filter: int = ..., flags: int = ..., fflags: int = ..., data: Any = ..., udata: Any = ...) -> None: ...
 
 # BSD only
 class kqueue(object):
@@ -104,7 +101,7 @@ class kqueue(object):
     def control(self, changelist: Optional[Iterable[kevent]], max_events: int, timeout: float = ...) -> List[kevent]: ...
     def fileno(self) -> int: ...
     @classmethod
-    def fromfd(cls, fd: _FileDescriptor) -> kqueue: ...
+    def fromfd(cls, fd: FileDescriptorLike) -> kqueue: ...
 
 # Linux only
 class epoll(object):
@@ -118,12 +115,12 @@ class epoll(object):
     def close(self) -> None: ...
     closed: bool
     def fileno(self) -> int: ...
-    def register(self, fd: _FileDescriptor, eventmask: int = ...) -> None: ...
-    def modify(self, fd: _FileDescriptor, eventmask: int) -> None: ...
-    def unregister(self, fd: _FileDescriptor) -> None: ...
+    def register(self, fd: FileDescriptorLike, eventmask: int = ...) -> None: ...
+    def modify(self, fd: FileDescriptorLike, eventmask: int) -> None: ...
+    def unregister(self, fd: FileDescriptorLike) -> None: ...
     def poll(self, timeout: float = ..., maxevents: int = ...) -> List[Tuple[int, int]]: ...
     @classmethod
-    def fromfd(cls, fd: _FileDescriptor) -> epoll: ...
+    def fromfd(cls, fd: FileDescriptorLike) -> epoll: ...
 
 if sys.version_info >= (3, 3):
     # Solaris only
@@ -132,7 +129,7 @@ if sys.version_info >= (3, 3):
             def close(self) -> None: ...
             closed: bool
             def fileno(self) -> int: ...
-        def register(self, fd: _FileDescriptor, eventmask: int = ...) -> None: ...
-        def modify(self, fd: _FileDescriptor, eventmask: int = ...) -> None: ...
-        def unregister(self, fd: _FileDescriptor) -> None: ...
+        def register(self, fd: FileDescriptorLike, eventmask: int = ...) -> None: ...
+        def modify(self, fd: FileDescriptorLike, eventmask: int = ...) -> None: ...
+        def unregister(self, fd: FileDescriptorLike) -> None: ...
         def poll(self, timeout: Optional[float] = ...) -> List[Tuple[int, int]]: ...

stdlib/2and3/termios.pyi

@@ -1,8 +1,8 @@
 # Stubs for termios
 
 from typing import IO, List, Union
+from _types import FileDescriptorLike
 
-_FD = Union[int, IO[str]]
 _Attr = List[Union[int, List[bytes]]]
 
 # TODO constants not really documented
@@ -238,11 +238,11 @@ VWERASE: int
 XCASE: int
 XTABS: int
 
-def tcgetattr(fd: _FD) -> _Attr: ...
-def tcsetattr(fd: _FD, when: int, attributes: _Attr) -> None: ...
-def tcsendbreak(fd: _FD, duration: int) -> None: ...
-def tcdrain(fd: _FD) -> None: ...
-def tcflush(fd: _FD, queue: int) -> None: ...
-def tcflow(fd: _FD, action: int) -> None: ...
+def tcgetattr(fd: FileDescriptorLike) -> _Attr: ...
+def tcsetattr(fd: FileDescriptorLike, when: int, attributes: _Attr) -> None: ...
+def tcsendbreak(fd: FileDescriptorLike, duration: int) -> None: ...
+def tcdrain(fd: FileDescriptorLike) -> None: ...
+def tcflush(fd: FileDescriptorLike, queue: int) -> None: ...
+def tcflow(fd: FileDescriptorLike, action: int) -> None: ...
 
 class error(Exception): ...