Add Ractor support

[wanabe]

Hello,

I added some changes to ruby/erb to support Ractor.

• Make ERB::NOT_GIVEN ractor-shareable
• Make @scanner_map of ERB::Compiler::Scanner ractor-shareable
  • I referred ruby/did_you_mean@8faba54
  • Only main Ractor can call ERB::Compiler::Scanner#register_scanner

And I confirmed that:

• It doesn't affect to ERB's behavior with ruby-2.7.0
• It allows us to call ERB.new and ERB#result in Ractor with ruby >= 3.1.0
• It can't allow us call ERB#result with ruby-3.0.x unfortunately
  • Because of the specification of Ractor on ruby-3.0.x:
    • "can not access instance variables of classes/modules from non-main Ractors"

$ for e in ALL_RUBY_BINS='ruby-2.5.0 ruby-2.6.0 ruby-2.7.0' ALL_RUBY_SINCE=ruby-3.0.0; do docker run -it -v .:/erb --rm rubylang/all-ruby env "$e" ./all-ruby -I/erb/lib -W0 -e 'begin; require "erb"; p [ERB.new("<%= 1 + 2 %>").result, defined?(Ractor) && Ractor.new { ERB.new("<%= 3 + 4 %>").result(binding) rescue [$!, $@[0]] }.take]; rescue; p $!; end'; done
ruby-2.5.0 #<NoMethodError: undefined method `resolve_feature_path' for #<Array:0x00005615de7f43e8>>
ruby-2.6.0 #<NoMethodError: undefined method `resolve_feature_path' for #<Array:0x000055faf5283390>>
ruby-2.7.0 ["3", nil]
ruby-3.0.0          ["3", [#<Ractor::IsolationError: can not access instance variables of classes/modules from non-main Ractors>, "/erb/lib/erb/compiler.rb:102:in `make_scanner'"]]
...
ruby-3.0.7          ["3", [#<Ractor::IsolationError: can not access instance variables of classes/modules from non-main Ractors>, "/erb/lib/erb/compiler.rb:102:in `make_scanner'"]]
ruby-3.1.0-preview1 ["3", "7"]
...
ruby-3.4.1          ["3", "7"]

[k0kubun]

👌