Add _collections_abc module (#4000)

* Add _collections_abc module
* Rearrange collections.abc and collections to re-export from _collections_abc

Co-authored-by: Sebastian Rittau <srittau@rittau.biz>

stdlib/3/_collections_abc.pyi

@@ -0,0 +1,56 @@
+from typing import (
+    AbstractSet as Set,
+    AsyncGenerator as AsyncGenerator,
+    AsyncIterable as AsyncIterable,
+    AsyncIterator as AsyncIterator,
+    Awaitable as Awaitable,
+    ByteString as ByteString,
+    Callable as Callable,
+    Collection as Collection,
+    Container as Container,
+    Coroutine as Coroutine,
+    Generator as Generator,
+    Hashable as Hashable,
+    ItemsView as ItemsView,
+    Iterable as Iterable,
+    Iterator as Iterator,
+    KeysView as KeysView,
+    Mapping as Mapping,
+    MappingView as MappingView,
+    MutableMapping as MutableMapping,
+    MutableSequence as MutableSequence,
+    MutableSet as MutableSet,
+    Reversible as Reversible,
+    Sequence as Sequence,
+    Sized as Sized,
+    ValuesView as ValuesView,
+)
+
+# Without the real definition, mypy and pytest both think that __all__ is empty, so re-exports nothing
+__all__ = [
+    "Awaitable",
+    "Coroutine",
+    "AsyncIterable",
+    "AsyncIterator",
+    "AsyncGenerator",
+    "Hashable",
+    "Iterable",
+    "Iterator",
+    "Generator",
+    "Reversible",
+    "Sized",
+    "Container",
+    "Callable",
+    "Collection",
+    "Set",
+    "MutableSet",
+    "Mapping",
+    "MutableMapping",
+    "MappingView",
+    "KeysView",
+    "ItemsView",
+    "ValuesView",
+    "Sequence",
+    "MutableSequence",
+    "ByteString",
+]

stdlib/3/collections/__init__.pyi

@@ -1,44 +1,9 @@
 import sys
 import typing
-from typing import (
-    AbstractSet,
-    Any,
-    AsyncGenerator as AsyncGenerator,
-    AsyncIterable as AsyncIterable,
-    AsyncIterator as AsyncIterator,
-    Awaitable as Awaitable,
-    ByteString as ByteString,
-    Callable as Callable,
-    Collection as Collection,
-    Container as Container,
-    Coroutine as Coroutine,
-    Dict,
-    Generator as Generator,
-    Generic,
-    Hashable as Hashable,
-    ItemsView as ItemsView,
-    Iterable as Iterable,
-    Iterator as Iterator,
-    KeysView as KeysView,
-    List,
-    Mapping as Mapping,
-    MappingView as MappingView,
-    MutableMapping as MutableMapping,
-    MutableSequence as MutableSequence,
-    MutableSet as MutableSet,
-    Optional,
-    Reversible as Reversible,
-    Sequence as Sequence,
-    Sized as Sized,
-    Tuple,
-    Type,
-    TypeVar,
-    Union,
-    ValuesView as ValuesView,
-    overload,
-)
+from typing import Any, Dict, Generic, List, Optional, Tuple, Type, TypeVar, Union, overload
 
-Set = AbstractSet
+if sys.version_info < (3, 10):
+    from _collections_abc import *
 
 _S = TypeVar("_S")
 _T = TypeVar("_T")

stdlib/3/collections/abc.pyi

@@ -1,27 +1,2 @@
-from . import (
-    AsyncGenerator as AsyncGenerator,
-    AsyncIterable as AsyncIterable,
-    AsyncIterator as AsyncIterator,
-    Awaitable as Awaitable,
-    ByteString as ByteString,
-    Callable as Callable,
-    Collection as Collection,
-    Container as Container,
-    Coroutine as Coroutine,
-    Generator as Generator,
-    Hashable as Hashable,
-    ItemsView as ItemsView,
-    Iterable as Iterable,
-    Iterator as Iterator,
-    KeysView as KeysView,
-    Mapping as Mapping,
-    MappingView as MappingView,
-    MutableMapping as MutableMapping,
-    MutableSequence as MutableSequence,
-    MutableSet as MutableSet,
-    Reversible as Reversible,
-    Sequence as Sequence,
-    Set as Set,
-    Sized as Sized,
-    ValuesView as ValuesView,
-)
+from _collections_abc import *
+from _collections_abc import __all__ as __all__