Fix stub for SpooledTemporaryFile (#2452)

Fixes #2431

stdlib/3/tempfile.pyi

@@ -5,7 +5,7 @@
 
 import sys
 from types import TracebackType
-from typing import Any, AnyStr, Generic, IO, Optional, Tuple, Type
+from typing import Any, AnyStr, Generic, IO, Iterable, Iterator, List, Optional, Tuple, Type
 
 # global variables
 TMP_MAX: int
@@ -26,12 +26,41 @@ if sys.version_info >= (3, 5):
         dir: Optional[AnyStr] = ..., delete: bool = ...
     ) -> IO[Any]:
         ...
-    def SpooledTemporaryFile(
-        max_size: int = ..., mode: str = ..., buffering: int = ...,
-        encoding: str = ..., newline: str = ..., suffix: Optional[AnyStr] = ...,
-        prefix: Optional[AnyStr] = ..., dir: Optional[AnyStr] = ...
-    ) -> IO[Any]:
-        ...
+
+    # It does not actually derive from IO[AnyStr], but it does implement the
+    # protocol.
+    class SpooledTemporaryFile(IO[AnyStr]):
+        def __init__(self, max_size: int = ..., mode: str = ...,
+                     buffering: int = ..., encoding: Optional[str] = ...,
+                     newline: Optional[str] = ..., suffix: Optional[str] = ...,
+                     prefix: Optional[str] = ..., dir: Optional[str] = ...
+                     ) -> None: ...
+        def rollover(self) -> None: ...
+        def __enter__(self) -> SpooledTemporaryFile: ...
+        def __exit__(self, exc_type: Optional[Type[BaseException]],
+                     exc_val: Optional[BaseException],
+                     exc_tb: Optional[TracebackType]) -> bool: ...
+
+        # These methods are copied from the abstract methods of IO, because
+        # SpooledTemporaryFile implements IO.
+        # See also https://github.com/python/typeshed/pull/2452#issuecomment-420657918.
+        def close(self) -> None: ...
+        def fileno(self) -> int: ...
+        def flush(self) -> None: ...
+        def isatty(self) -> bool: ...
+        def read(self, n: int = ...) -> AnyStr: ...
+        def readable(self) -> bool: ...
+        def readline(self, limit: int = ...) -> AnyStr: ...
+        def readlines(self, hint: int = ...) -> List[AnyStr]: ...
+        def seek(self, offset: int, whence: int = ...) -> int: ...
+        def seekable(self) -> bool: ...
+        def tell(self) -> int: ...
+        def truncate(self, size: Optional[int] = ...) -> int: ...
+        def writable(self) -> bool: ...
+        def write(self, s: AnyStr) -> int: ...
+        def writelines(self, lines: Iterable[AnyStr]) -> None: ...
+        def __next__(self) -> AnyStr: ...
+        def __iter__(self) -> Iterator[AnyStr]: ...
 
     class TemporaryDirectory(Generic[AnyStr]):
         name = ...  # type: str