Finding an object's referrers

object_referrers.rb

require 'objspace'
require 'fiddle'
require 'json'

def heap
  $heap ||= ObjectSpace
    .dump_all(output: :string)
    .lines.map { JSON.parse _1, symbolize_names: true }
    .reject { |obj| %w[ROOT IMEMO DATA].include? obj[:type] } # probably overzealous
end

public def referrers
  my_addr = JSON.parse(ObjectSpace.dump self, output: :string)['address']
  heap.select { |obj| obj[:references]&.include? my_addr }  # find referrers
      .filter_map { |obj| obj[:address] }                   # get their hex address if they have one
      .map { |addr| addr[2..-1].to_i(16) }                  # convert to int address
      .map { |addr| Fiddle::Pointer.new(addr).to_value }    # convert to Ruby reference
end

User   = Struct.new :id, :name
Users  = Struct.new :all
user1  = User.new 123, "Josh"
user2  = User.new 456, "Sal"
@users = Users.new [user1, user2]

# "Josh" shows up somewhere in the app
# We can see it came from User 123
# Which came from an array
# Stored by Users#all
# stored by main (in `@users`, but main's inspect doesn't show its ivars)
user1.name          # => "Josh"
  .referrers.first  # => #<struct User id=123, name="Josh">
  .referrers.first  # => [#<struct User id=123, name="Josh">, #<struct User id=456, name="Sal">]
  .referrers.first  # => #<struct Users all=[#<struct User id=123, name="Josh">, #<struct User id=456, name="Sal">]>
  .referrers.first  # => main