Fix return types in urllib.request (#2389)

* Tighten return types of URL handlers

* urlopen() etc. return a modified HTTPResponse

* Add missing methods to HTTPResponse

Author: srittau

stdlib/3/http/client.pyi

@@ -104,6 +104,9 @@ if sys.version_info >= (3, 5):
         def __exit__(self, exc_type: Optional[Type[BaseException]],
                      exc_val: Optional[BaseException],
                      exc_tb: Optional[types.TracebackType]) -> bool: ...
+        def info(self) -> email.message.Message: ...
+        def geturl(self) -> str: ...
+        def getcode(self) -> int: ...
 else:
     class HTTPResponse(io.RawIOBase, BinaryIO):  # type: ignore
         msg = ...  # type: HTTPMessage
@@ -126,6 +129,9 @@ else:
         def __exit__(self, exc_type: Optional[Type[BaseException]],
                      exc_val: Optional[BaseException],
                      exc_tb: Optional[types.TracebackType]) -> bool: ...
+        def info(self) -> email.message.Message: ...
+        def geturl(self) -> str: ...
+        def getcode(self) -> int: ...
 
 class HTTPConnection:
     if sys.version_info >= (3, 7):

stdlib/3/urllib/request.pyi

@@ -2,7 +2,7 @@
 
 from typing import (
     Any, Callable, ClassVar, Dict, List, IO, Mapping, Optional, Sequence, Tuple,
-    TypeVar, Union, overload,
+    TypeVar, Union, overload, NoReturn,
 )
 from http.client import HTTPResponse, HTTPMessage
 from http.cookiejar import CookieJar
@@ -13,8 +13,11 @@ import sys
 import os
 
 _T = TypeVar('_T')
-_UrlopenRet = Union[HTTPResponse, addinfourl]
+_UrlopenRet = Union[_HTTPResponse, addinfourl]
 
+class _HTTPResponse(HTTPResponse):
+    url: str
+    msg: str  # type: ignore
 
 def urlopen(
     url: Union[str, Request], data: Optional[bytes] = ...,
@@ -155,33 +158,33 @@ class ProxyDigestAuthHandler(BaseHandler, AbstractDigestAuthHandler):
                        hdrs: Mapping[str, str]) -> Optional[_UrlopenRet]: ...
 
 class HTTPHandler(BaseHandler):
-    def http_open(self, req: Request) -> _UrlopenRet: ...
+    def http_open(self, req: Request) -> HTTPResponse: ...
 
 class HTTPSHandler(BaseHandler):
     def __init__(self, debuglevel: int = ...,
                  context: Optional[ssl.SSLContext] = ...,
                  check_hostname: bool = ...) -> None: ...
-    def https_open(self, req: Request) -> _UrlopenRet: ...
+    def https_open(self, req: Request) -> HTTPResponse: ...
 
 class FileHandler(BaseHandler):
-    def file_open(self, req: Request) -> _UrlopenRet: ...
+    def file_open(self, req: Request) -> addinfourl: ...
 
 class DataHandler(BaseHandler):
-    def data_open(self, req: Request) -> _UrlopenRet: ...
+    def data_open(self, req: Request) -> addinfourl: ...
 
 class FTPHandler(BaseHandler):
-    def ftp_open(self, req: Request) -> _UrlopenRet: ...
+    def ftp_open(self, req: Request) -> addinfourl: ...
 
 class CacheFTPHandler(FTPHandler):
     def setTimeout(self, t: float) -> None: ...
     def setMaxConns(self, m: int) -> None: ...
 
 class UnknownHandler(BaseHandler):
-    def unknown_open(self, req: Request) -> _UrlopenRet: ...
+    def unknown_open(self, req: Request) -> NoReturn: ...
 
 class HTTPErrorProcessor(BaseHandler):
-    def http_response(self) -> _UrlopenRet: ...
-    def https_response(self) -> _UrlopenRet: ...
+    def http_response(self, request, response) -> _UrlopenRet: ...
+    def https_response(self, request, response) -> _UrlopenRet: ...
 
 if sys.version_info >= (3, 6):
     def urlretrieve(url: str, filename: Optional[Union[str, os.PathLike]] = ...,