Unexpected behaviour with Ruby's rescue allowing calling of any setter method instead of local variable assignment.

rescue_hack.rb

explicit_receiver = Object.new
def explicit_receiver.setter=(error)
  puts "setter= called with #{error.class}"
end

begin
  1 / 0
rescue => explicit_receiver.setter
  # There doesn't seem to be a restriction on rescue setting local variables.
  # Ruby seems to take whatever appears in the rescue clause
  #     rescue => ____
  # and use it to run
  #     ____ = error
  # which then follows normal assignment semantics:
  # - assigns local variable unless explicit receiver
  # - sends ____= message to said receiver
end

# This can be turned into the following monstrosity

# Assuming you're using an error reporting framework like Bugsnag
# and it has an API like this:
module Bugsnag
  def self.notify(error)
    puts "\n\nW͇̖̮̰̘͛̉̏̏̌̚h̫̬̺̫̞̅̓a̡̞͇̪̖̜̲̎͐t́̓ͣͥͪ҉̣̜͔ ̼̟̖̈ͭh̵͕̙̭̠̭̀͋a̪̳ͯv̬̺̟̤̯̼̫̀̓͊̒̓̂e͙͈͗ͭͮͫͤͦͩ̀ ͈̹ͥ͋ͫ̄͛͒ͬI͉͖͇̫̳̤̟ͤ͆̉ ̲̹̮̩̤̭ͨ͗̾ͣ̍̉̓d͆̕ȯ̺̩͍ͭ͒ͯ̿ͅn̻͖͎̲̒͟e̜̽̌͌ͯ̾̚͟?͎\n\n"
  end
end

# You can do
Bugsnag.singleton_class.alias_method :notify=, :notify

# and then
begin
  1 / 0
rescue => Bugsnag.notify
end