Implement __hash__ for GraphQLError

graphql/error/graphql_error.py

@@ -79,6 +79,8 @@ class GraphQLError(Exception):
         "extensions",
     )
 
+    __hash__ = Exception.__hash__
+
     def __init__(
         self,
         message: str,
@@ -89,7 +91,7 @@ def __init__(
         original_error: Exception = None,
         extensions: Dict[str, Any] = None,
     ) -> None:
-        super(GraphQLError, self).__init__(message)
+        super().__init__(message)
         self.message = message
         if nodes and not isinstance(nodes, list):
             nodes = [nodes]  # type: ignore

tests/error/test_graphql_error.py

@@ -126,3 +126,11 @@ def default_error_formatter_includes_extension_fields():
             "path": None,
             "extensions": {"foo": "bar"},
         }
+
+    def is_hashable():
+        hash(GraphQLError("msg"))
+
+    def hashes_are_unique_per_instance():
+        e1 = GraphQLError("msg")
+        e2 = GraphQLError("msg")
+        assert hash(e1) != hash(e2)