Define protocols for connection type overrides

Author: Mark Edwards

Diff for: pyproject.toml

@@ -31,6 +31,7 @@ packages = [
 [tool.poetry.dependencies]
 python = "^3.6"
 graphql-core = "^3.0"
+typing-extensions = "^3.6.2"
 
 [tool.poetry.dev-dependencies]
 pytest = "^5.3"

Diff for: src/graphql_relay/connection/arrayconnection.py

@@ -1,6 +1,7 @@
 import binascii
 import warnings
-from typing import Any, Optional, Sequence
+from typing import Any, List, Optional, Sequence
+from typing_extensions import Protocol
 
 from ..utils.base64 import base64, unbase64
 from .connectiontypes import (
@@ -21,13 +22,59 @@
 ]
 
 
+class EdgeType(Protocol):
+    @property
+    def node(self) -> Any: ...
+    @property
+    def cursor(self) -> ConnectionCursor: ...
+
+
+class EdgeConstructor(Protocol):
+    def __call__(self, *, node: Any, cursor: ConnectionCursor) -> EdgeType: ...
+
+
+class PageInfoType(Protocol):
+    @property
+    def startCursor(self) -> Optional[ConnectionCursor]: ...
+    def endCursor(self) -> Optional[ConnectionCursor]: ...
+    def hasPreviousPage(self) -> Optional[bool]: ...
+    def hasNextPage(self) -> Optional[bool]: ...
+
+
+class PageInfoConstructor(Protocol):
+    def __call__(
+        self,
+        *,
+        startCursor: Optional[ConnectionCursor],
+        endCursor: Optional[ConnectionCursor],
+        hasPreviousPage: Optional[bool],
+        hasNextPage: Optional[bool],
+    ) -> PageInfoType: ...
+
+
+class ConnectionType(Protocol):
+    @property
+    def edges(self): List[EdgeType]: ...
+    @property
+    def pageInfo(self): PageInfoType: ...
+
+
+class ConnectionConstructor(Protocol):
+    def __call__(
+        self,
+        *,
+        edges: List[EdgeType],
+        pageInfo: PageInfoType,
+    ) -> ConnectionType: ...
+
+
 def connection_from_array(
     data: Sequence,
     args: ConnectionArguments = None,
-    connection_type: Any = Connection,
-    edge_type: Any = Edge,
-    page_info_type: Any = PageInfo,
-) -> Connection:
+    connection_type: ConnectionConstructor = Connection,
+    edge_type: EdgeConstructor = Edge,
+    page_info_type: PageInfoConstructor = PageInfo,
+) -> ConnectionType:
     """Create a connection object from a sequence of objects.
 
     Note that different from its JavaScript counterpart which expects an array,
@@ -54,10 +101,10 @@ def connection_from_array(
 def connection_from_list(
     data: Sequence,
     args: ConnectionArguments = None,
-    connection_type: Any = Connection,
-    edge_type: Any = Edge,
-    pageinfo_type: Any = PageInfo,
-) -> Connection:
+    connection_type: ConnectionConstructor = Connection,
+    edge_type: EdgeConstructor = Edge,
+    pageinfo_type: PageInfoConstructor = PageInfo,
+) -> ConnectionType:
     """Deprecated alias for connection_from_array.
 
     We're now using the JavaScript terminology in Python as well, since list
@@ -84,10 +131,10 @@ def connection_from_array_slice(
     slice_start: int = 0,
     array_length: int = None,
     array_slice_length: int = None,
-    connection_type: Any = Connection,
-    edge_type: Any = Edge,
-    page_info_type: Any = PageInfo,
-) -> Connection:
+    connection_type: ConnectionConstructor = Connection,
+    edge_type: EdgeConstructor = Edge,
+    page_info_type: PageInfoConstructor = PageInfo,
+) -> ConnectionType:
     """Create a connection object from a slice of the result set.
 
     Note that different from its JavaScript counterpart which expects an array,
@@ -162,13 +209,13 @@ def connection_from_array_slice(
 def connection_from_list_slice(
     list_slice: Sequence,
     args: ConnectionArguments = None,
-    connection_type: Any = Connection,
-    edge_type: Any = Edge,
-    pageinfo_type: Any = PageInfo,
+    connection_type: ConnectionConstructor = Connection,
+    edge_type: EdgeConstructor = Edge,
+    pageinfo_type: PageInfoConstructor = PageInfo,
     slice_start=0,
     list_length=0,
     list_slice_length=None,
-) -> Connection:
+) -> ConnectionType:
     """Deprecated alias for connection_from_array_slice.
 
     We're now using the JavaScript terminology in Python as well, since list