ruby on rails - How can I remove a default gem? ! want to uninstall a gem 1.7.7 version of json

Question

I have the same rails app in OSX and Ubuntu, I want to use Zeus to speed up my rspec. In Ubuntu, Zeus starts Ok, but in OSX it always be crashed. At last I find the issue, https://github.com/burke/zeus/issues/237#issuecomment-18700462 the difference between OSX and Ubuntu is the version of json gem. I use gem list | grep json Ubuntu shows

json (1.8.1, 1.8.0, 1.5.3)
json_pure (1.5.3)
json_spec (1.1.1)
jsonpath (0.5.3)
multi_json (1.8.2, 1.7.8, 1.0.3)

Mac shows

json (1.8.1, 1.7.7)
json_spec (1.1.1)
jsonpath (0.5.5, 0.5.3)
multi_json (1.8.2, 1.7.8)

so I want to uninstall 1.7.7 version of json gem to make zeus start, but

gem uninstall json -v 1.7.7
ERROR:  While executing gem ... (Gem::InstallError)
gem "json" cannot be uninstalled because it is a default gem

What should I do?

Answer 1

So based off what I can tell there is no easy command that can move the gemspec file from the default folder to the non-default folder. This is a good thing from what I can tell but here are the instructions on how to do this by hand.

1. Find the location of the default spec. The easiest way is to go into irb and run the following command:

   irb(main):002:0> Gem.default_specifications_dir
   => "/Users/user/.rubies/ruby-2.5.7/lib/ruby/gems/2.5.0/specifications/default"
   

   For older rubygems it's:

   irb(main):001:0> File.join Gem::Specification.default_specifications_dir
   => "/Users/newdark/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/specifications/default"
   

This is the line of code that builds the gemspec path https://github.com/rubygems/rubygems/blob/v2.6.13/lib/rubygems/installer.rb#L420

2. Once you get the file path you just need to move the gem name and version from the default folder to the parent folder.

   $ cd /Users/newdark/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/specifications/default
   $ mv json-1.7.7.gemspec ../
   

if you do gem list -d you should no longer see the words Installed at (default) next to the gem version json-1.7.7. you can then run gem uninstall json -v 1.7.7 with out it fighting you. If you want to undo all this just run gem install json -v 1.7.7 --default