Remove OpenStruct references from Jbuilder

[mtsmfm]

While I was looking at #562, I noticed OpenStruct never responses map and count method.

docker run rubylang/all-ruby ./all-ruby -e 'require "ostruct"; p [:map, :count].map {|m| OpenStruct.new({}).respond_to?(m) }'

ruby-1.6.0            [false, false]
...
ruby-3.3.1            [false, false]

ruby-0.49             -e:1: syntax error
                      -e:1: syntax error
                      -e:1: syntax error
                      -e:1: syntax error
                      -e:1: syntax error
                      -e:1: syntax error
                      -e:1: syntax error
                      -e:1: syntax error
                      -e:1: syntax error
                  exit 9
ruby-0.50             -e:1: syntax error
                      -e:1: syntax error
                      -e:1: syntax error
                      -e:1: syntax error
                      -e:1: syntax error
                      -e:1: syntax error
                      -e:1: syntax error
                      -e:1: syntax error
                      -e:1: syntax error
                  exit 9
ruby-0.51             -e:1: syntax error
                  exit 1
...
ruby-0.76             -e:1: syntax error
                  exit 1
ruby-0.95             -e:1:in `require': No such file to load -- ostruct
                  exit 1
ruby-0.99.4-961224    -e:1:in `require': No such file to load -- ostruct
                        from -e:1
                  exit 1
ruby-1.0-961225       -e:1:in `require': No such file to load -- ostruct
                        from -e:1
                  exit 1
ruby-1.0-971002       -e:1:in `require': LoadError: No such file to load -- ostruct
                        from -e:1
                  exit 1
...
ruby-1.0-971225       -e:1:in `require': LoadError: No such file to load -- ostruct
                        from -e:1
                  exit 1
ruby-1.1a0            -e:1:in `require': LoadError| No such file to load -- ostruct
                        from -e:1
                  exit 1
ruby-1.1a1            -e:1:in `require': LoadError| No such file to load -- ostruct
                        from -e:1
                  exit 1
ruby-1.1a2            -e:1:in `require': LoadError:No such file to load -- ostruct
                        from -e:1
                  exit 1
ruby-1.1a3            -e:1:in `require': LoadError: No such file to load -- ostruct
                        from -e:1
                  exit 1
...
ruby-1.1a9            -e:1:in `require': LoadError: No such file to load -- ostruct
                        from -e:1
                  exit 1
ruby-1.1b0            -e:1:in `require': No such file to load -- ostruct (LoadError)
                        from -e:1
                  exit 1
ruby-1.1b1            -e:1:in `require': No such file to load -- ostruct (LoadError)
                        from -e:1
                  exit 1
ruby-1.1b2            -e:1: undefined iterator `map' for [8017, 8025](Array) (NameError)
                  exit 1
ruby-1.1b3            -e:1: undefined iterator `map' for [8017, 8025](Array) (NameError)
                  exit 1
ruby-1.1b4            -e:1: undefined iterator `map' for [8017, 8025] (NameError)
                  exit 1
ruby-1.1b5            -e:1: undefined iterator `map' for [8025, 8033] (NameError)
                  exit 1
ruby-1.1b6            -e:1: undefined iterator `map' for [8001, 8009] (NameError)
                  exit 1
ruby-1.1b7            -e:1: undefined iterator `map' for [8065, 8073] (NameError)
                  exit 1
ruby-1.1b8            -e:1: undefined iterator `map' for [8081, 8089] (NameError)
                  exit 1
ruby-1.1b9            -e:1: undefined iterator `map' for [8081, 8089] (NameError)
                  exit 1
ruby-1.1b9_01         -e:1: undefined iterator `map' for [8121, 8129] (NameError)
                  exit 1
...
ruby-1.1b9_03         -e:1: undefined iterator `map' for [8121, 8129] (NameError)
                  exit 1
ruby-1.1b9_04         -e:1: undefined iterator `map' for [8145, 8153] (NameError)
                  exit 1
ruby-1.1b9_05         -e:1: undefined iterator `map' for [8161, 8169] (NameError)
                  exit 1
ruby-1.1b9_06         -e:1: undefined iterator `map' for [8177, 8185] (NameError)
                  exit 1
ruby-1.1b9_07         -e:1: undefined iterator `map' for [8241, 8249] (NameError)
                  exit 1
ruby-1.1b9_08         -e:1: undefined iterator `map' for [8249, 8257] (NameError)
                  exit 1
ruby-1.1b9_09         -e:1: undefined iterator `map' for [8241, 8249] (NameError)
                  exit 1
ruby-1.1b9_10         -e:1: undefined iterator `map' for [8265, 8273] (NameError)
                  exit 1
ruby-1.1b9_11         -e:1: undefined iterator `map' for [8281, 8289] (NameError)
                  exit 1
ruby-1.1b9_12         -e:1: undefined iterator `map' for [8289, 8297] (NameError)
                  exit 1
...
ruby-1.1b9_14         -e:1: undefined iterator `map' for [8289, 8297] (NameError)
                  exit 1
ruby-1.1b9_15         -e:1: undefined iterator `map' for [8305, 8313] (NameError)
                  exit 1
ruby-1.1b9_16         -e:1: undefined iterator `map' for [8321, 8329] (NameError)
                  exit 1
ruby-1.1b9_17         /tmp/rbeOxo3r:1: undefined iterator `map' for [8353, 8361] (NameError)
                  exit 1
ruby-1.1b9_18         /tmp/rbLXgKTu:1: undefined iterator `map' for [8361, 8369] (NameError)
                  exit 1
ruby-1.1b9_19         /tmp/rbzff2Rx:1: NameError
                  exit 1
ruby-1.1b9_20         /tmp/rbusengG:1: NameError
                  exit 1
ruby-1.1b9_21         /tmp/rb6y6OiI:1: undefined iterator `map' for [8361, 8369] (NameError)
                  exit 1
ruby-1.1b9_22         /tmp/rb2ECrEP:1: undefined iterator `map' for [8361, 8369] (NameError)
                  exit 1
ruby-1.1b9_23         /tmp/rbRjC3NS:1: undefined iterator `map' for [8377, 8385] (NameError)
                  exit 1
ruby-1.1b9_24         /tmp/rbe7hi1Y:1: undefined iterator `map' for [8393, 8401] (NameError)
                  exit 1
ruby-1.1b9_25         /tmp/rbd1IlwZ:1: undefined iterator `map' for [8393, 8401] (NameError)
                  exit 1
ruby-1.1b9_26         /tmp/rbaCV6E5:1: undefined iterator `map' for [8417, 8425] (NameError)
                  exit 1
ruby-1.1b9_27         /tmp/rbtsOvQc:1: undefined iterator `map' for [8417, 8425] (NameError)
                  exit 1
ruby-1.1b9_28         /tmp/rboLvSeg:1: undefined iterator `map' for [8417, 8425] (NameError)
                  exit 1
ruby-1.1b9_29         /tmp/rb2jEekm:1: undefined iterator `map' for [8433, 8441] (NameError)
                  exit 1
ruby-1.1b9_30         /tmp/rbKwAYsn:1: undefined iterator `map' for [8433, 8441] (NameError)
                  exit 1
ruby-1.1b9_31         /tmp/rbxT9q7t:1: undefined iterator `map' for [8433, 8441] (NameError)
                  exit 1
ruby-1.1b9_32         /tmp/rbqIT5Yz:1: undefined iterator `map' for [8433, 8441] (NameError)
                  exit 1
ruby-1.1c0            /tmp/rbx3kWwB:1: undefined iterator `map' for [8433, 8441] (NameError)
                  exit 1
ruby-1.1c1            /tmp/rbkA6tQG:1: undefined iterator `map' for [8433, 8441] (NameError)
                  exit 1
ruby-1.1c2            /tmp/rbjBlWzO:1: undefined iterator `map' for [8433, 8441] (NameError)
                  exit 1
ruby-1.1c3            /tmp/rbhSOmQO:1: undefined iterator `map' for [8433, 8441] (NameError)
                  exit 1
ruby-1.1c4            /tmp/rbcyRhDW:1: undefined iterator `map' for [8433, 8441] (NameError)
                  exit 1
ruby-1.1c5            /tmp/rbDCXRs0:1: undefined iterator `map' for [8433, 8441] (NameError)
                  exit 1
ruby-1.1c6            /tmp/rbGaLFU3:1: undefined iterator `map' for [8161, 8169] (NameError)
                  exit 1
ruby-1.1c7            /tmp/rbEJdNUa:1: undefined iterator `map' for [8169, 8177] (NameError)
                  exit 1
ruby-1.1c8            /tmp/rbqSgfCg:1: undefined iterator `map' for [8737, 8745] (NameError)
                  exit 1
ruby-1.1c9            /tmp/rb8cxY4g:1: undefined iterator `map' for [8169, 8177] (NameError)
                  exit 1
ruby-1.1d0            /tmp/rbE2S8lo:1: undefined iterator `map' for [8241, 8249] (NameError)
                  exit 1
ruby-1.1d1            /tmp/rbVN0Fet:1: undefined iterator `map' for [8241, 8249] (NameError)
                  exit 1
ruby-1.2              /tmp/rbZn9F4u:1: undefined iterator `map' for [8169, 8177] (NameError)
                  exit 1
ruby-1.2.1            /tmp/rbgpMTvB:1: undefined iterator `map' for [8169, 8177] (NameError)
                  exit 1
ruby-1.2.2            /tmp/rbsm7VeF:1: undefined iterator `map' for [8169, 8177] (NameError)
                  exit 1
ruby-1.2.3            /tmp/rbfnaYEL:1: undefined iterator `map' for [8169, 8177] (NameError)
                  exit 1
ruby-1.2.4            /tmp/rbXrp0aQ:1: undefined iterator `map' for [8169, 8177] (NameError)
                  exit 1
ruby-1.2.5            /tmp/rbw3le0S:1: undefined iterator `map' for [8169, 8177] (NameError)
                  exit 1
ruby-1.2.6            /tmp/rbuoXmWY:1: undefined iterator `map' for [8169, 8177] (NameError)
                  exit 1
ruby-1.3              /tmp/rbH4Vxa2:1: undefined iterator `map' for [8241, 8249] (NameError)
                  exit 1
ruby-1.3.1-990215     /tmp/rbJiv876:1: undefined iterator `map' for [8409, 8417] (NameError)
                  exit 1
ruby-1.3.1-990224     /tmp/rbGx9f0d:1: undefined iterator `map' for [8417, 8425] (NameError)
                  exit 1
ruby-1.3.1-990225     /tmp/rbpkHQFh:1: undefined iterator `map' for [8417, 8425] (NameError)
                  exit 1
ruby-1.3.1-990311     /tmp/rbEhjCXo:1: undefined iterator `map' for [8473, 8481] (NameError)
                  exit 1
ruby-1.3.1-990315     /tmp/rbrcYwYq:1: undefined iterator `map' for [8497, 8505] (NameError)
                  exit 1
ruby-1.3.1-990324     /tmp/rb5U9Lmu:1: undefined iterator `map' for [8513, 8521] (NameError)
                  exit 1
ruby-1.3.2-990402     /tmp/rbJp4WPy:1: undefined iterator `map' for [8529, 8537] (NameError)
                  exit 1
ruby-1.3.2-990405     /tmp/rbmhN9zD:1: undefined iterator `map' for [8529, 8537] (NameError)
                  exit 1
ruby-1.3.2-990408     /tmp/rbDtyMjL:1: undefined iterator `map' for [8529, 8537] (NameError)
                  exit 1
ruby-1.3.2-990413     /tmp/rbzOHQlP:1: undefined iterator `map' for [8529, 8537] (NameError)
                  exit 1
ruby-1.3.3-990430     /tmp/rbFjs8TT:1: undefined iterator `map' for [8537, 8545] (NameError)
                  exit 1
ruby-1.3.3-990507     /tmp/rbP7X9VX:1: undefined iterator `map' for [8537, 8545] (NameError)
                  exit 1
ruby-1.3.3-990513     /tmp/rbuVw2S3:1: undefined iterator `map' for [8537, 8545] (NameError)
                  exit 1
ruby-1.3.3-990518     /tmp/rbkTUut6:1: undefined iterator `map' for [8545, 8553] (NameError)
                  exit 1
ruby-1.3.4-990531     /tmp/rbAKdS4b:1: undefined iterator `map' for [8553, 4225] (NameError)
                  exit 1
ruby-1.3.4-990611     /tmp/rb1IMDCf:1: undefined iterator `map' for [8585, 4233] (NameError)
                  exit 1
ruby-1.3.4-990624     /tmp/rbHKJQ8k:1: undefined iterator `map' for [8585, 4233] (NameError)
                  exit 1
ruby-1.3.4-990625     /tmp/rbatRIFp:1: undefined iterator `map' for [8585, 4233] (NameError)
                  exit 1
ruby-1.3.5            /tmp/rbV1nV7t:1: undefined method `map' for [8585, 4233]:Array (NameError)
                  exit 1
ruby-1.3.6            /tmp/rbmbWPQy:1: undefined method `map' for [8585, 4233]:Array (NameError)
                  exit 1
ruby-1.3.7            /tmp/rbx0D9fG:1: undefined method `map' for [8593, 4233]:Array (NameError)
                  exit 1
ruby-1.4.0            /tmp/rbTiBWPH:1: undefined method `map' for [8593, 4233]:Array (NameError)
                  exit 1
ruby-1.4.1            /tmp/rbatNtEO:1: undefined method `map' for [8593, 4233]:Array (NameError)
                  exit 1
ruby-1.4.2            /tmp/rbbhuiuQ:1: undefined method `map' for [8593, 4233]:Array (NameError)
                  exit 1
ruby-1.4.3            /tmp/rbW4ACmW:1: undefined method `map' for [8593, 4233]:Array (NameError)
                  exit 1
ruby-1.4.4            /tmp/rb5aEcr3:1: undefined method `map' for [8593, 4233]:Array (NameError)
                  exit 1
ruby-1.4.5            /tmp/rbjJF5T6:1: undefined method `map' for [8601, 4233]:Array (NameError)
                  exit 1
ruby-1.4.6            /tmp/rbJxuXgb:1: undefined method `map' for [8601, 4233]:Array (NameError)
                  exit 1
ruby-1.6.0            [false, false]
...
ruby-3.3.1            [false, false]

So, even we remove OpenStruct related codes completely, Jbuilder can handle them

require 'bundler/inline'

gemfile do
  source 'https://rubygems.org'

  if ENV['FORK']
    gem 'jbuilder', path: '.'
  else
    gem 'jbuilder'
  end
end

puts "Jbuilder::NON_ENUMERABLES: #{Jbuilder.const_defined?("NON_ENUMERABLES")}"

require 'ostruct'

ostruct = OpenStruct.new(a: 1)
struct = Struct.new(:a).new(a: 1)

array = [{a: 1}]

result = Jbuilder.new do |json|
  json.array array, :a
  json.struct struct, :a
  json.ostruct ostruct, :a
  json.array_struct [struct], :a
  json.array_ostruct [ostruct], :a
end.target!

if JSON.parse(result) == {"array"=>[{"a"=>1}], "struct"=>{"a"=>1}, "ostruct"=>{"a"=>1}, "array_struct"=>[{"a"=>1}], "array_ostruct"=>[{"a"=>1}]}
  puts 'Passed'
else
  puts 'Failed'
end

__END__
$ ruby foo.rb
Jbuilder::NON_ENUMERABLES: true
Passed

$ FORK=1 ruby foo.rb
Jbuilder::NON_ENUMERABLES: false
Passed

But if an OpenStruct instance has both map and count fields, it would be broken.

require 'bundler/inline'

gemfile do
  source 'https://rubygems.org'

  if ENV['FORK']
    gem 'jbuilder', path: '.'
  else
    gem 'jbuilder'
  end
end

puts "Jbuilder::NON_ENUMERABLES: #{Jbuilder.const_defined?("NON_ENUMERABLES")}"

require 'ostruct'

ostruct = OpenStruct.new(a: 1, count: 1, map: 1)

result = Jbuilder.new do |json|
  json.ostruct ostruct, :a
end.target!

if JSON.parse(result) == {"ostruct"=>{"a"=>1}}
  puts 'Passed'
else
  puts 'Failed'
end

__END__

$ ruby broken.rb
Jbuilder::NON_ENUMERABLES: true
Passed

$ FORK=1 ruby broken.rb
Jbuilder::NON_ENUMERABLES: false
/workspaces/jbuilder/lib/jbuilder.rb:339:in `-': Array can't be coerced into Integer (TypeError)

    end - [BLANK]
          ^^^^^^^
        from /workspaces/jbuilder/lib/jbuilder.rb:339:in `_map_collection'
        from /workspaces/jbuilder/lib/jbuilder.rb:217:in `array!'
        from /workspaces/jbuilder/lib/jbuilder.rb:56:in `block in set!'
        from /workspaces/jbuilder/lib/jbuilder.rb:345:in `_scope'
        from /workspaces/jbuilder/lib/jbuilder.rb:56:in `set!'
        from /workspaces/jbuilder/lib/jbuilder.rb:70:in `method_missing'
        from broken.rb:20:in `block in <main>'
        from /workspaces/jbuilder/lib/jbuilder.rb:21:in `initialize'
        from broken.rb:19:in `new'
        from broken.rb:19:in `<main>'

So, strictly speaking, this change is a breaking change.

What do you think?

If you don't agree with this change, you can just close this PR.
I just want to tell you another possibility.

[mtsmfm]

With Ruby 3.4, a newly created Rails application immediately shows a warning about ostruct

$ docker run --rm -it ruby:3.4.0-preview1 bash -c "gem install rails && rails new foo && cd foo && echo test && bin/rails r 'puts %(hi)'"
(snip)
test
/usr/local/bundle/gems/bootsnap-1.18.3/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:30: warning: /usr/local/lib/ruby/3.4.0+0/ostruct.rb was loaded from the standard library, but will no longer be part of the default gems since Ruby 3.5.0. Add ostruct to your Gemfile or gemspec.
hi

With this patch, such warning won't be appeared since it completely removes the require thing for ostruct.

$ docker run --rm -it ruby:3.4.0-preview1 bash -c "gem install rails && rails new foo && cd foo && sed -i 's;gem \"jbuilder\";gem \"jbuilder\", github: \"mtsmfm/jbuilder\", branch: \"remove-ostruct\";' Gemfile && bundle install && echo test && bin/rails r 'puts %(hi)'"
(snip)
test
hi