Improve pymysql types (#1804)

Add all cursor types and missing show_warnings method in connections

Added show_warnings to connections. No return type specified as this
requires tracing back through missing return types in previous
author's work. This is out of scope for this pull request.

Added SSDictCursor, SSCursor and DictCursorMixin to complete the
Cursors definition.

third_party/2and3/pymysql/connections.pyi

@@ -100,10 +100,10 @@ class Connection:
     def __enter__(self): ...
     def __exit__(self, exc, value, traceback): ...
     def query(self, sql): ...
-    def next_result(self): ...
+    def next_result(self, unbuffered: bool = ...): ...
     def affected_rows(self): ...
     def kill(self, thread_id): ...
-    def ping(self, reconnect=True): ...
+    def ping(self, reconnect: bool = ...): ...
     def set_charset(self, charset): ...
     def read_packet(self, packet_type=...): ...
     def insert_id(self): ...
@@ -112,6 +112,7 @@ class Connection:
     def get_host_info(self): ...
     def get_proto_info(self): ...
     def get_server_info(self): ...
+    def show_warnings(self): ...
     Warning = ...  # type: Any
     Error = ...  # type: Any
     InterfaceError = ...  # type: Any

third_party/2and3/pymysql/cursors.pyi

@@ -1,4 +1,4 @@
-from typing import Union, Tuple, Any, Dict, Optional, Text
+from typing import Union, Tuple, Any, Dict, Optional, Text, Iterator, List
 from .connections import Connection
 
 Gen = Union[Tuple[Any, ...], Dict[str, Any]]
@@ -22,12 +22,25 @@ class Cursor:
     def executemany(self, query: str, args) -> int: ...
     def callproc(self, procname, args=...): ...
     def fetchone(self) -> Optional[Gen]: ...
-    def fetchmany(self, size: Optional[int] = ...) -> Optional[Gen]: ...
+    def fetchmany(self, size: Optional[int] = ...) -> Union[Optional[Gen], List[Gen]]: ...
     def fetchall(self) -> Optional[Tuple[Gen, ...]]: ...
-    def scroll(self, value, mode=''): ...
+    def scroll(self, value: int, mode: str = ...): ...
     def __iter__(self): ...
 
 class DictCursor(Cursor):
     def fetchone(self) -> Optional[Dict[str, Any]]: ...
-    def fetchmany(self, size=None) -> Optional[Tuple[Dict[str, Any], ...]]: ...
+    def fetchmany(self, size: Optional[int] = ...) -> Optional[Tuple[Dict[str, Any], ...]]: ...
     def fetchall(self) -> Optional[Tuple[Dict[str, Any], ...]]: ...
+
+class DictCursorMixin:
+    dict_type = ...  # type: Any
+
+class SSCursor(Cursor):
+    # fetchall return type is incompatible with the supertype.
+    def fetchall(self) -> List[Gen]: ...  # type: ignore
+    def fetchall_unbuffered(self) -> Iterator[Tuple[Gen, ...]]: ...
+    def __iter__(self) -> Iterator[Tuple[Gen, ...]]: ...
+    def fetchmany(self, size: Optional[int] = ...) -> List[Gen]: ...
+    def scroll(self, value: int, mode: str = ...) -> None: ...
+
+class SSDictCursor(DictCursorMixin, SSCursor): ...