alias_method_chain and prepend

a_m_c_and_prepend.rb

# 1. alias_method before prepend
module PreA
  def foo
    puts "pre a"
    super
  end
end

class A
  def self.foo
    puts "A"
  end
end

class A
  class << self
    def foo_with_chain
      puts "foo_with_hcain"
      foo_without_chain
    end
    alias_method_chain :foo, :chain
  end
end

class A
  class << self
    prepend PreA
  end
end

A.foo()

# 2. alias_method after prepend
module PreA
  def foo
    puts "pre a"
    super
  end
end

class A
  def self.foo
   puts "A"
  end
end


class A
  class << self
    prepend PreA
  end
end

class A
  class << self

    def foo_with_chain
      puts "foo_with_hcain"
      foo_without_chain
    end
    alias_method_chain :foo, :chain
  end
end

A.foo()

###############################################################################################
#  "SystemStackError: stack level too deep" test error in af_xx gem tests when removing a_m_c #
###############################################################################################

###########
# example #
###########

# ruby -Itest test/af_job/queue_test.rb -n test_enqueue
# Run options: -n test_enqueue

# Running tests:

# Error:
# AfJob::QueueTest#test_enqueue:
# SystemStackError: stack level too deep
#    /Users/yunlei/.rvm/gems/ruby-2.1.5/gems/newrelic_rpm-3.9.8.273/lib/new_relic/agent/traced_method_stack.rb:83

# Finished tests in 0.084935s, 11.7737 tests/s, 0.0000 assertions/s.
# 1 tests, 0 assertions, 0 failures, 1 errors, 0 skips

# The reason it failed here is that:
# In the test_helper of this unit test, `af_job` which contains the prepend stuff is required before the `test_app`,
# and when the test_app is required, it will add ActiveRecord transaction tracer by using newrelic_rpm(using alias_method way).
# then it hit the first case metioned above.

#############################################
# Why it not failed in property app level ? #
#############################################
# because newrelic_rpm is a dependency for property app which will be loaded before our app level prepend stuff.

######################
# Future work        #
######################
# make the gem test works, decouple the dependency