Bring back #arg_rest local

Author: kddnewton

lib/prism/debug.rb

@@ -59,7 +59,21 @@ def self.cruby_locals(source)
  stack = [ISeq.new(RubyVM::InstructionSequence.compile(source).to_a)]
 
  while (iseq = stack.pop)
- locals << iseq.local_table
+ names = [*iseq.local_table]
+ names.map!.with_index do |name, index|
+ # When an anonymous local variable is present in the iseq's local
+ # table, it is represented as the stack offset from the top.
+ # However, when these are dumped to binary and read back in, they
+ # are replaced with the symbol :#arg_rest. To consistently handle
+ # this, we replace them here with their index.
+ if name == :"#arg_rest"
+ names.length - index + 1
+ else
+ name
+ end
+ end
+
+ locals << names
  iseq.each_child { |child| stack << child }
  end