invalid GEM_HOME due to new MRI 2.1.x versioning scheme

[Jon]

• on *nix, gems installed incorrectly into ~/.gem/ruby/2.1.x instead of ~/.gem/ruby/2.1.0
• on *nix, uru specified PATH incorrectly munged similar to /home/jon/.gem/ruby/2.1.1/bin:/home/jon/.rubies/ruby-2.1.0/bin:::...

[Jon]

This code is no longer correct for MRI 2.1.0

According to this MRI post it appears that uru should set GEM_HOME to /home/$USER/.gem/$RUBY_ENGINE/$MAJOR.$MINOR.0 for 2.1+.

Here we go again with MRI's versioning dance. First the 1.9.3 -> 1.9.1 lib version fiasco which uru handled by morphing GEM_HOME so that 1.9.3 -> 1.9.3 lib version. Now uru may have to reverse course for 2.1.x so that 2.1.0, 2.1.1, 2.1.2 -> 2.1.0 lib version

[Michał Papis]

just a side note, 2.1.0 comes with RG 2.2 which has support for shared gem home with building of extensions on demand (you can have one GEM_HOME for all rubies on rubygems 2.2)

[Jon]

@mpapis ah, I need to get up to speed on those features. Thank you.

How are you handling 2.1.0 versioning with RVM? (I haven't browsed your BitBucket RVM repo yet)

[Michał Papis]

RVM 1.x has only one way of handling GEM_HOME - every ruby gets rvm/gems/full_name@global + rvm/gems/full_name where @global is inherited via GEM_PATH by all other gemsets on "fullname" ruby - @gemset is a way to allow you have multiple sets of gems

[Jon]

Learn new MRI 2.1.0 versioning. Closes #52

Any MRI 2.1.0 rubies registered with uru 0.7.1 or earlier must be reregistered. Uru generated incorrect GEM_HOME values for MRI 2.1.0 rubies at registration time.

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