Hello - We are currently in the process of upgrading our Jruby application to Rails 5, and have discovered an issue with the axslx gem, which appears to stem from a Jruby bug. There is an issue open regarding this here:
randym/axlsx#533

This gem uses Array.instance_methods to delegate methods to an internal array. The gem works fine on the Rails 4-2 stable branch. I did some digging and discovered there is some strange behavior using prepend, which is used in Rails 5 on the Enumerable module. If the prepended module is included, and then prepended the including class will not show the modules methods in its instance_methods method.

Example from Rails:

In Rails 4-2 stable using Jruby 9.1.12.0:

 Array.instance_methods.include?(:each_with_index)
=> true

In Rails 5-1 stable using Jruby 9.1.12.0:

Array.instance_methods.include?(:each_with_index)
=> false

I think I reproduced the problem below outside of Rails. Let me know if you need anymore information.

Environment

Provide at least:

• JRuby version: jruby 9.1.12.0

Expected Behavior

module A
def a
end
end

module B
def b
end
end

module C
def c
end
end

class D
include A
include B
end

D.instance_methods.include?(:b)
=> true

B.prepend C

D.instance_methods.include?(:b)
=> true

Actual Behavior

D.instance_methods.include?(:b)
=> true

B.prepend C

D.instance_methods.include?(:b)
=> false