feat(relay): add option for strict connection types (#1504)

* types: add option for strict connection types

* chore: appease linter

* chore: appease linter

* test: add test

---------

Co-authored-by: Erik Wrede <erikwrede@users.noreply.github.com>

Author: garobrik

graphene/relay/connection.py

@@ -13,12 +13,18 @@
 
 
 def get_edge_class(
-    connection_class: Type["Connection"], _node: Type[AbstractNode], base_name: str
+    connection_class: Type["Connection"],
+    _node: Type[AbstractNode],
+    base_name: str,
+    strict_types: bool = False,
 ):
     edge_class = getattr(connection_class, "Edge", None)
 
     class EdgeBase:
-        node = Field(_node, description="The item at the end of the edge")
+        node = Field(
+            NonNull(_node) if strict_types else _node,
+            description="The item at the end of the edge",
+        )
         cursor = String(required=True, description="A cursor for use in pagination")
 
     class EdgeMeta:
@@ -83,7 +89,9 @@ class Meta:
         abstract = True
 
     @classmethod
-    def __init_subclass_with_meta__(cls, node=None, name=None, _meta=None, **options):
+    def __init_subclass_with_meta__(
+        cls, node=None, name=None, strict_types=False, _meta=None, **options
+    ):
         if not _meta:
             _meta = ConnectionOptions(cls)
         assert node, f"You have to provide a node in {cls.__name__}.Meta"
@@ -111,10 +119,10 @@ def __init_subclass_with_meta__(cls, node=None, name=None, _meta=None, **options
             )
 
         if "edges" not in _meta.fields:
-            edge_class = get_edge_class(cls, node, base_name)  # type: ignore
+            edge_class = get_edge_class(cls, node, base_name, strict_types)  # type: ignore
             cls.Edge = edge_class
             _meta.fields["edges"] = Field(
-                NonNull(List(edge_class)),
+                NonNull(List(NonNull(edge_class) if strict_types else edge_class)),
                 description="Contains the nodes in this connection.",
             )
 

graphene/relay/tests/test_connection.py

@@ -299,3 +299,20 @@ def resolve_test_connection(root, info, **args):
     executed = schema.execute("{ testConnection { edges { cursor } } }")
     assert not executed.errors
     assert executed.data == {"testConnection": {"edges": []}}
+
+
+def test_connectionfield_strict_types():
+    class MyObjectConnection(Connection):
+        class Meta:
+            node = MyObject
+            strict_types = True
+
+    connection_field = ConnectionField(MyObjectConnection)
+    edges_field_type = connection_field.type._meta.fields["edges"].type
+    assert isinstance(edges_field_type, NonNull)
+
+    edges_list_element_type = edges_field_type.of_type.of_type
+    assert isinstance(edges_list_element_type, NonNull)
+
+    node_field = edges_list_element_type.of_type._meta.fields["node"]
+    assert isinstance(node_field.type, NonNull)