build_followpos

# File actionpack/lib/action_dispatch/journey/gtg/builder.rb, line 129
          def build_followpos
            table = Hash.new { |h, k| h[k] = [] }.compare_by_identity
            @ast.each do |n|
              case n
              when Nodes::Cat
                lastpos(n.left).each do |i|
                  table[i] += firstpos(n.right)
                end
              end
            end
            table
          end