Use private_method_defined? instead of respond_to?

[mame]

Module.respond_to?(:ruby2_keywords, true) does NOT check if
Module#ruby2_keywords is available. It worked well because there is
toplevel ruby2_keywords method, but using private_method_defined? is
better, I think.

Also, this fixes a syntactic error.

[benlangfeld]

This broke this gem on Ruby 2.5:

ArgumentError: wrong number of arguments (given 2, expected 1)
/usr/local/bundle/gems/ruby2_keywords-0.0.3/lib/ruby2_keywords.rb:2:in `private_method_defined?'

[benlangfeld]

This broke this gem on Ruby 2.5:

ArgumentError: wrong number of arguments (given 2, expected 1)
/usr/local/bundle/gems/ruby2_keywords-0.0.3/lib/ruby2_keywords.rb:2:in `private_method_defined?'

[eregon]

It also broke TruffleRuby FWIW (notably, gem install sinatra fails now).
Of course we'll fix TruffleRuby master to handle 2-args private_method_defined?, but it won't fix existing releases, notably 21.0.0 coming out today.

Module.respond_to?(:ruby2_keywords, true) does NOT check if
Module#ruby2_keywords is available.

I believe that's incorrect.

respond_to?(:ruby2_keywords, true) is what everyone uses, and AFAIK it's correct, it finds Module#ruby2_keywords:

ruby -ve 'class Module; p method(:ruby2_keywords).owner; end'
ruby 2.7.2p137 (2020-10-01 revision 5445e04352) [x86_64-linux]
Module

i.e., we check if self == #<Class:Module>, which is an instance of Class < Module has a method ruby2_keywords, and yes, there is Module#ruby2_keywords.

Please revert and re-release.

[eregon]

That's an incorrect check BTW, there is Hash.ruby2_keywords_hash? and no Hash#ruby2_keywords_hash?.

[eregon]

Nobu fixed it in 51c47c0.