Annotate werkzeug wrap_file() and FileWrapper (#2519)

* Add FileWrapper protocol to wsgiref.types

* Annotate werkzeug's wrap_file and FileWrapper

* Remove empty line at end of file

* Fix _Readable protocols

stdlib/2and3/wsgiref/types.pyi

@@ -36,3 +36,9 @@ class ErrorStream(Protocol):
     def flush(self) -> None: ...
     def write(self, s: str) -> None: ...
     def writelines(self, seq: List[str]) -> None: ...
+
+class _Readable(Protocol):
+    def read(self, size: int = ...) -> bytes: ...
+# Optional file wrapper in wsgi.file_wrapper
+class FileWrapper(Protocol):
+    def __call__(self, file: _Readable, block_size: int = ...) -> Iterable[bytes]: ...

third_party/2and3/werkzeug/wsgi.pyi

@@ -1,4 +1,4 @@
-from typing import Any, Optional
+from typing import Any, Optional, Protocol, Iterable
 from wsgiref.types import WSGIEnvironment, InputStream
 
 def responder(f): ...
@@ -40,18 +40,21 @@ class ClosingIterator:
     def __next__(self): ...
     def close(self): ...
 
-def wrap_file(environ, file, buffer_size=8192): ...
+class _Readable(Protocol):
+    def read(self, size: int = ...) -> bytes: ...
+
+def wrap_file(environ: WSGIEnvironment, file: _Readable, buffer_size: int = ...) -> Iterable[bytes]: ...
 
 class FileWrapper:
-    file = ...  # type: Any
-    buffer_size = ...  # type: Any
-    def __init__(self, file, buffer_size=8192): ...
-    def close(self): ...
-    def seekable(self): ...
-    def seek(self, *args): ...
-    def tell(self): ...
-    def __iter__(self): ...
-    def __next__(self): ...
+    file: _Readable
+    buffer_size: int
+    def __init__(self, file: _Readable, buffer_size: int = ...) -> None: ...
+    def close(self) -> None: ...
+    def seekable(self) -> bool: ...
+    def seek(self, offset: int, whence: int = ...) -> None: ...
+    def tell(self) -> Optional[int]: ...
+    def __iter__(self) -> FileWrapper: ...
+    def __next__(self) -> bytes: ...
 
 class _RangeWrapper:
     iterable = ...  # type: Any