decouple the `join_constraints` method from the parent pointer

activerecord/lib/active_record/associations/join_dependency.rb

@@ -80,7 +80,7 @@ def merge_outer_joins!(other)
       end
 
       def join_constraints
-        join_root.children.flat_map { |c| c.flat_map(&:join_constraints) }
+        make_joins join_root
       end
 
       def columns
@@ -111,6 +111,12 @@ def instantiate(result_set)
 
       private
 
+      def make_joins(node)
+        node.children.flat_map { |child|
+          child.join_constraints(node).concat make_joins(child)
+        }
+      end
+
       def merge_node(left, right)
         intersection, missing = right.children.map { |node1|
           [left.children.find { |node2| node1.match? node2 }, node1]

activerecord/lib/active_record/associations/join_dependency/join_association.rb

@@ -38,7 +38,7 @@ def match?(other)
           super && reflection == other.reflection
         end
 
-        def join_constraints
+        def join_constraints(parent)
           joins         = []
           tables        = @tables.dup