deduplicate interfaces higher up

Author: dleavitt

lib/graphql/schema/member/has_interfaces.rb

@@ -33,9 +33,9 @@ def implements(*new_interfaces, **options)
             end
           end
 
-          # Remove any String or late-bound interfaces which are being replaced
           own_interface_type_memberships.reject! { |old_i_m|
             if !(old_i_m.respond_to?(:abstract_type) && old_i_m.abstract_type.is_a?(Module))
+              # Remove any String or late-bound interfaces which are being replaced
               old_int_type = old_i_m.respond_to?(:abstract_type) ? old_i_m.abstract_type : old_i_m
               old_name = Schema::Member::BuildType.to_type_name(old_int_type)
 
@@ -45,6 +45,11 @@ def implements(*new_interfaces, **options)
 
                 new_name == old_name
               }
+            elsif old_i_m.respond_to?(:abstract_type)
+              # Remove any existing implementations of the same interface
+              new_memberships.any? { |new_i_m|
+                new_i_m.respond_to?(:abstract_type) && new_i_m.abstract_type == old_i_m.abstract_type
+              }
             end
           }
           own_interface_type_memberships.concat(new_memberships)
@@ -80,7 +85,7 @@ def interfaces(context = GraphQL::Query::NullContext)
             visible_interfaces.concat(superclass.interfaces(context))
           end
 
-          visible_interfaces.uniq
+          visible_interfaces
         end
       end
     end