Open Radar

 
OS X 10.11 customizes the Rubygems installation location to ensure that gems' binaries aren't written to /usr/bin, which would be disallowed by SIP, but to /usr/local/bin.

To do this, rubygems/defaults.rb from the builtin rubygems is patched: http://opensource.apple.com/source/ruby/ruby-113/patches/lib_rubygems_defaults.rb.diff

However, if the user upgrades Rubygems itself using `sudo /usr/bin/gem update --system`, Rubygems will install a new copy of itself in /Library/Ruby which contains an unpatched rubygems/defaults.rb, causing Rubygems to attempt to install gem binaries to /usr/bin again.

Rubygems provides a file to cover this usecase; if rubygems/defaults/operating_system.rb exists, it takes precedence over rubygems/defaults.rb. Apple should ship this file with the required customizations instead of patching rubygems/defaults.rb.

Related to rdar://22979372

Steps to Reproduce:
1. Run sudo /usr/bin/gem update --system

Expected Results:
Rubygems continues to work as expected.

Actual Results:
`/usr/bin/gem install` invocations will fail when gem binary installations are attempted to /usr/bin, and SIP prevents it.