(Translated by Google :))
If you try to use some default gems with fixed version using Bundler, there are cases where the current Rubygems / Bundler / Ruby specification can not be used with the version specified by the user.
For example
$ ruby -v
ruby 2.4.1p111 (2017-03-22 revision 58053) [x86_64-darwin17]
$ gem list | grep openssl
openssl (2.0.5, 2.0.4, default: 2.0.3)
In the environment such as require 'openssl', the version that is activated when openssl is searched with openssl is the version found first, ie 2.0.5.
$ ruby -ropenssl -e 'p OpenSSL::VERSION'
"2.0.5"
At this time, for example, suppose the user really wants to use openssl 2.0.4 and wrote the following Gemfile.
> cat Gemfile
# frozen_string_literal: true
source "https://rubygems.org"
gem 'openssl', '2.0.4'
Unfortunately, since rubygems has required openssl before the bundler runs it will result in an activated error like this:
> bundle exec ruby -ropenssl -e 'p OpenSSL::VERSION'
/path/to/2.4.1/lib/ruby/gems/2.4.0/gems/bundler-1.15.4/lib/bundler/runtime.rb:317:in `check_for_activated_spec!': You have already activated openssl 2.0.5, but your Gemfile requires openssl 2.0.4. Prepending `bundle exec` to your command may solve this. (Gem::LoadError)
This problem can be avoided by bundling it as a vendoring library under bundler's repository if it is a default gem implemented with pure ruby.
Https://github.com/bundler/bundler/blob/master/lib/bundler/vendor/fileutils/lib/fileutils.rb
In the case of bundler, by separating the namespace as Bundler::FileUtils, even the version specified by the user is made available without conflict at the time of activate. However, this method can not be used with C extention library.
Since we want to use json/psych from the bundler team with rubygems/bundler to serialize data, we need about whether we can implement a way to avoid some kind of C extension on Ruby itself.
Consult @hsbt and @indirect, for example
require_for_bundler 'json', '2.0.2'
Once I talked that it could be avoided if json-2.0.2 (which is the version shipped with ruby 2.4.1) is placed in a namespace like Bundler::JSON. There were similar issues in the past as well.
https://bugs.ruby-lang.org/issues/10320
I think that the way of writing require 'json', version: '2.0.2', into: :Bundler which extended the method like this issue seems like that. Also, in this use case, it seems to be enough to use require 'json', version: :default, into: :Bundler which forces the use of default gem.
Matz, How do you think about this feature?