Add NoReturn type to typing stubs

Author: Michael0x2a

stdlib/2/typing.pyi

@@ -24,6 +24,11 @@ ClassVar: _SpecialForm = ...
 
 class GenericMeta(type): ...
 
+# Return type that indicates a function does not return.
+# This type is equivalent to the None type, but the no-op Union is necessary to
+# distinguish the None type from the None value.
+NoReturn = typing.Union[None]
+
 # Type aliases and type constructors
 
 class TypeAlias:

stdlib/3/typing.pyi

@@ -25,6 +25,11 @@ ClassVar: _SpecialForm = ...
 
 class GenericMeta(type): ...
 
+# Return type that indicates a function does not return.
+# This type is equivalent to the None type, but the no-op Union is necessary to
+# distinguish the None type from the None value.
+NoReturn = typing.Union[None]
+
 # Type aliases and type constructors
 
 class TypeAlias: