cmp different from the string representation

Đọc phần triển khai cmp trong ext/pathname/pathname.c và các trường hợp liên quan trong test/pathname/test_pathname.rb, sau đó tái hiện các kết quả khác nhau của Pathname#<=> và thứ tự chuỗi được mô tả trong issue. Được xem là hoàn tất khi hành vi sắp xếp dự kiến đã được xác lập và các bài kiểm thử hoặc tài liệu liên quan phản ánh rõ ràng kết luận đó.

There's an ordering difference when using the built-in <=> vs the string representation one:

> Pathname.new(File.expand_path('.')).glob('**/*.rb').sort.first(5)
=> [#<Pathname:/Users/pirj/source/rspec-dev/repos/rspec-mocks/lib/rspec/mocks/any_instance/chain.rb>,
 #<Pathname:/Users/pirj/source/rspec-dev/repos/rspec-mocks/lib/rspec/mocks/any_instance/error_generator.rb>,
 #<Pathname:/Users/pirj/source/rspec-dev/repos/rspec-mocks/lib/rspec/mocks/any_instance/expect_chain_chain.rb>,
 #<Pathname:/Users/pirj/source/rspec-dev/repos/rspec-mocks/lib/rspec/mocks/any_instance/expectation_chain.rb>,
 #<Pathname:/Users/pirj/source/rspec-dev/repos/rspec-mocks/lib/rspec/mocks/any_instance/message_chains.rb>]
> Pathname.new(File.expand_path('.')).glob('**/*.rb').sort_by(&:to_s).first(5)
=> [#<Pathname:/Users/pirj/source/rspec-dev/repos/rspec-mocks/lib/rspec/mocks.rb>,
 #<Pathname:/Users/pirj/source/rspec-dev/repos/rspec-mocks/lib/rspec/mocks/any_instance.rb>,
 #<Pathname:/Users/pirj/source/rspec-dev/repos/rspec-mocks/lib/rspec/mocks/any_instance/chain.rb>,
 #<Pathname:/Users/pirj/source/rspec-dev/repos/rspec-mocks/lib/rspec/mocks/any_instance/error_generator.rb>,
 #<Pathname:/Users/pirj/source/rspec-dev/repos/rspec-mocks/lib/rspec/mocks/any_instance/expect_chain_chain.rb>]

And the latter corresponds to the classic alternative:

> Dir[File.expand_path('**/*.rb')].sort.first(5)
=> ["/Users/pirj/source/rspec-dev/repos/rspec-mocks/lib/rspec/mocks.rb",
 "/Users/pirj/source/rspec-dev/repos/rspec-mocks/lib/rspec/mocks/any_instance.rb",
 "/Users/pirj/source/rspec-dev/repos/rspec-mocks/lib/rspec/mocks/any_instance/chain.rb",
 "/Users/pirj/source/rspec-dev/repos/rspec-mocks/lib/rspec/mocks/any_instance/error_generator.rb",
 "/Users/pirj/source/rspec-dev/repos/rspec-mocks/lib/rspec/mocks/any_instance/expect_chain_chain.rb"]

Just by looking at the cmp implementation and tests I couldn't understand, is this the designed behaviour, or the behaviour is undefined?

Semantically, it would make sense to load rspec/mocks.rb first, and then rspec/mocks/any_instance.rb, not the other way around.
Some discussion in rspec-rails regarding the issues it may cause.
rspec-rails PR to change the helper template to use Pathname#glob instead of Dir.[].

A workaround rspec-rails plans to take is to sort_by(&:to_s) to get back to the string representation-like ordering.

(semi-)Related cops:

• https://docs.rubocop.org/rubocop-rails/cops_rails.html#railsrootpathnamemethods
• https://docs.rubocop.org/rubocop/1.65/cops_lint.html#lintnondeterministicrequireorder