irb_syntax_checker_checker.rb

require 'prism'
require 'irb'

# Collect syntax-valid code snippets from the given directory
def each_snippet(dir, max_size)
  files = Dir.glob("#{dir.delete_suffix('/')}/**/*.rb")
  snippets = Set.new
  handle_snippet = ->(code) {
    return if snippets.include?(code)
    snippets << code
    yield code
  }
  files.each do |file|
    p file

    code = File.read(file) rescue next
    node = Prism.parse(code).value
    node.breadth_first_search do |n|
      if n.slice.size < max_size && Prism.parse_success?(n.slice)
        handle_snippet.call(n.slice)
      end
      # Test code may include ruby-code as a string literal
      if n.is_a?(Prism::StringNode) && n.slice.size < max_size && Prism.parse_success?(n.unescaped)
        handle_snippet.call(n.unescaped)
      end
      false
    end
  end
end

# Split the snippet into code, newline, post and create an incomplete but recoverable code
def test_snippet(snippet)
  [*0..snippet.size].sample(10).each do |len|
    code = snippet[0, len] + "\n"
    post = snippet[len..]
    next unless !Prism.parse_success?(code) && Prism.parse_success?(code + post)
    check_code(code, post)
  end
end

def check_code(recoverable_error_code, next_line_code)
  status = IRB::RubyLex.new.check_code_syntax(recoverable_error_code, local_variables: [])

  case status
  when :valid
    raise 'unreachable'
  when :recoverable_error
    # Expected
  when :unrecoverable_error
    p BUG: [status, recoverable_error_code, next_line_code]
  when :other_error
  end
end

each_snippet(ARGV[0] || '.', 500) do |snippet|
  test_snippet(snippet)
end