Fix show_source command when obj.method is overrided

[tompng]

method method is sometimes overridden.

req = Net::HTTP::Post.new('/path')
req.method #=> "POST"
req.path #=> "/path"

Fixes this error

irb(main):001> require 'net/http'
=> true
irb(main):002> req = Net::HTTP::Post.new('/path')
=> #<Net::HTTP::Post POST>
irb(main):003> $ req.path
lib/irb/source_finder.rb:117:in 'IRB::SourceFinder#method_target': wrong number of arguments (given 1, expected 0) (ArgumentError)

        target_method = owner_receiver.method(method)
                                              ^^^^^^

[st0012]

I think we already store the method method in KERNEL_METHOD under Context. Perhaps we can create a module under IRB, like IRB::ORIGINAL_METHODS::KERNEL_METHOD, to host these method objects and reuse them in different places?

[tompng]

It'd be good to introduce something like IRB::ORIGINAL_METHODS 👍

In context.rb and in completion.rb, method is called in each keystroke. But in SourceFinder, it is only called once per show_source. Needs for storing is not that high here, so I want to pend doing it for now in this pull request.

Anyway, thanks for finding KERNEL_METHOD. I updated Object.instance_method(:method) to Kernel.instance_method(:method) since def method; end in top level overrides Object's method.

[st0012]

That's fair. Feel free to ship it then!