"gem install" with jruby-complete results in "missing class name (`org.jruby.util.Classpath')"

[rtyler]

On the current JRuby 1.7.21-SNAPSHOT (md5sum: 726148282565527249367b129c22bad8 jruby-complete-1.7.21-20150626.195528-6.jar) there are some gems which will result in the "missing class name" error from above, e.g.:

Negative case

➜  classpath-repro  java -jar jruby-complete-1.7.21-20150626.195528-6.jar -S gem install ./diff-lcs-1.2.5.gem --ignore-dependencies --install-dir=./gems --no-user-install --wrappers --no-document --local
ERROR:  While executing gem ... (NameError)
    missing class name (`org.jruby.util.Classpath')
➜  classpath-repro  

I found this also occurs with Rack:

➜  classpath-repro  java -jar jruby-complete-1.7.21-20150626.195528-6.jar -S gem install ./rack-1.6.4.gem --ignore-dependencies --install-dir=./gems --no-user-install --wrappers --no-document --local
ERROR:  While executing gem ... (NameError)
    missing class name (`org.jruby.util.Classpath')
➜  classpath-repro  

Positive case

Other gems, such as thread_safe do not have this problem:

➜  classpath-repro  java -jar jruby-complete-1.7.21-20150626.195528-6.jar -S gem install ./thread_safe-0.3.5.gem --ignore-dependencies --install-dir=./gems --no-user-install --wrappers --no-document --local
Successfully installed thread_safe-0.3.5
1 gem installed
➜  classpath-repro  

On JRuby 1.7.20.1

It does not reproduce with these gems on 1.7.20.1 however:

➜  classpath-repro  java -jar jruby-complete-1.7.20.1.jar -S gem install ./rack-1.6.4.gem --ignore-dependencies --install-dir=./gems --no-user-install --wrappers --no-document --local
Successfully installed rack-1.6.4
1 gem installed
➜  classpath-repro  

[rtyler]

One other interesting thing to note, it appears that gems/gems/rack-1.6.4 is present, so some portion of the installation succeeded