Rails deep_munge patch

deep_munge_fix.rb

# This is a monkey patch to fix the Rails deep_munge issue described here:
# https://github.com/rails/rails/issues/13420
#
# Rails converts incoming empty array params into nils. This patch reverts that.
# This goes in /config/initializers
#
# Before patch:
#
# | JSON                             | Hash                    |
# |----------------------------------|-------------------------|
# | { "person": null }               | { 'person' => nil }     |
# | { "person": [] }                 | { 'person' => nil }     |
# | { "person": [null] }             | { 'person' => nil }     |
# | { "person": [null, null, ...] }  | { 'person' => nil }     |
# | { "person": ["foo", null] }      | { 'person' => ["foo"] } |
#
# After patch:
#
# | JSON                             | Hash                    |
# |----------------------------------|-------------------------|
# | { "person": null }               | { 'person' => nil }     |
# | { "person": [] }                 | { 'person' => [] }      |
# | { "person": [null] }             | { 'person' => [] }      |
# | { "person": [null, null, ...] }  | { 'person' => [] }      |
# | { "person": ["foo", null] }      | { 'person' => ["foo"] } |


class DeepMungeFix
  def self.patch
    if test_query_params("test[]") == { "test" => nil }
      apply_patch

      unless test_query_params("test[]") == { "test" => [] }
        raise "patch failed!"
      end
    else
      raise "deep_munge patch not applied. Maybe this was fixed in this version of Rails?"
    end
  end

  def self.test_query_params(query_string)
    ActionDispatch::Request.new('QUERY_STRING' => query_string).query_parameters
  end

  def self.apply_patch
    ActionDispatch::Request.class_eval do
      def deep_munge(hash)
        hash.each do |k, v|
          case v
          when Array
            v.grep(Hash) { |x| deep_munge(x) }
            v.compact!
            ## This patch removes the next line
            # hash[k] = nil if v.empty?
          when Hash
            deep_munge(v)
          end
        end

        hash
      end
    end
  end
end

DeepMungeFix.patch