Add NoReturn (#811)

* Add NoReturn

stdlib/2/__builtin__.pyi

@@ -11,6 +11,7 @@ from typing import (
     MutableSet, ItemsView, KeysView, ValuesView, Optional, Container,
 )
 from abc import abstractmethod, ABCMeta
+from mypy_extensions import NoReturn
 
 _T = TypeVar('_T')
 _T_co = TypeVar('_T_co', covariant=True)
@@ -682,7 +683,7 @@ def dir(o: object = ...) -> List[str]: ...
 def divmod(a: int, b: int) -> Tuple[int, int]: ...
 @overload
 def divmod(a: float, b: float) -> Tuple[float, float]: ...
-def exit(code: int = ...) -> None: ...
+def exit(code: int = ...) -> NoReturn: ...
 @overload
 def filter(function: Callable[[_T], Any],
            iterable: Iterable[_T]) -> List[_T]: ...

stdlib/2/os/__init__.pyi

@@ -5,6 +5,7 @@ from typing import (
     Dict, MutableMapping, NamedTuple, overload
 )
 from . import path
+from mypy_extensions import NoReturn
 
 error = OSError
 name = ...  # type: str
@@ -185,7 +186,7 @@ def execvpe(file: AnyStr, args: Union[Tuple[AnyStr], List[AnyStr]], env: Mapping
 def execv(path: AnyStr, args: Union[Tuple[AnyStr], List[AnyStr]]) -> None: ...
 def execve(path: AnyStr, args: Union[Tuple[AnyStr], List[AnyStr]], env: Mapping[AnyStr, AnyStr]) -> None: ...
 
-def _exit(n: int) -> None: ...
+def _exit(n: int) -> NoReturn: ...
 
 def fork() -> int: ...
 def forkpty() -> Tuple[int, int]: ...

stdlib/2/sys.pyi

@@ -5,6 +5,7 @@ from typing import (
     overload, Type,
 )
 from types import FrameType, ModuleType, TracebackType, ClassType
+from mypy_extensions import NoReturn
 
 class _flags:
     bytes_warning = ...  # type: int
@@ -118,7 +119,7 @@ def exc_info() -> Tuple[Optional[Type[BaseException]],
                         Optional[TracebackType]]: ...
 
 # sys.exit() accepts an optional argument of anything printable
-def exit(arg: Any = ...) -> None:
+def exit(arg: Any = ...) -> NoReturn:
     raise SystemExit()
 def getcheckinterval() -> int: ...  # deprecated
 def getdefaultencoding() -> str: ...