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RubyVM::InstructionSequence.compile_file uses parse.y instead of prism when called from IRB #1212
Description
Ref: rails/bootsnap#539
I can't explain why it happens.
Reproduction, paste in IRB:
puts RUBY_DESCRIPTION
File.write("/tmp/prism-repro.rb", <<~'RUBY')
def foo(bars)
case bars
in [one, "a" | "b" => two]
puts "#{one} - #{two}"
end
end
RUBY
RubyVM::InstructionSequence.compile_file("/tmp/prism-repro.rb")Result:
ruby 4.0.2 (2026-03-17 revision d3da9fec82) +PRISM [arm64-darwin25]
(irb):21:in 'RubyVM::InstructionSequence.compile_file':
/tmp/prism-repro.rb:3: alternative pattern after variable capture (SyntaxError)
in [one, "a" | "b" => two]
^
from (irb):21:in '<main>'
from /Users/byroot/.gem/rubies/4.0.2/gems/irb-1.18.0/exe/irb:9:in '<top (required)>'
from /opt/rubies/4.0.2/lib/ruby/4.0.0/rubygems.rb:304:in 'Kernel#load'
from /opt/rubies/4.0.2/lib/ruby/4.0.0/rubygems.rb:304:in 'Gem.activate_and_load_bin_path'
from /Users/byroot/.gem/rubies/4.0.2/bin/irb:25:in '<main>'
This is failing because in Ruby 4.0.2 parse.y has a bug, but the important part here is that this is using parse.y even though the default Ruby parser in that session is supposed to be prism.
Interestingly, RubyVM::InstructionSequence.compile doesn't seem to have this problem.
Activity
byroot commentedon May 4, 2026
Nevermind, seem to be caused by ruby/ruby#16463, I'll ask for a backport.