Improve validation error message when field names conflict

Related GraphQL-js commit: graphql/graphql-js@6103d2d

Author: syrusakbary

graphql/validation/rules/overlapping_fields_can_be_merged.py

@@ -257,7 +257,11 @@ def collect_field_asts_and_defs(self, parent_type, selection_set, visited_fragme
 
     @classmethod
     def fields_conflict_message(cls, reason_name, reason):
-        return 'Fields "{}" conflict because {}'.format(reason_name, cls.reason_message(reason))
+        return (
+            'Fields "{}" conflict because {}. '
+            'Use different aliases on the fields to fetch both if this was '
+            'intentional.'
+        ).format(reason_name, cls.reason_message(reason))
 
     @classmethod
     def reason_message(cls, reason):

graphql/validation/tests/test_overlapping_fields_can_be_merged.py

@@ -635,3 +635,13 @@ def test_ignores_unknown_types():
         }
     }
     ''')
+
+
+def test_error_message_contains_hint_for_alias_conflict():
+    error = OverlappingFieldsCanBeMerged.fields_conflict_message('x', 'a and b are different fields')
+    hint = (
+        'Fields "x" conflict because a and b are different fields. '
+        'Use different aliases on the fields to fetch both '
+        'if this was intentional.'
+    )
+    assert error == hint