Rdoc data for core and stdlib is not in our distribution

[ghost]

Steps to reproduce

1. Download JRuby 9.1.15.0 Binary .tar.gz from http://jruby.org/download
2. tar -xf jruby-dist-9.1.15.0-bin.tar.gz
3. mv jruby-9.1.15.0 $HOME
4. PATH=$PATH:$HOME/jruby-9.1.15.0/bin
5. which ri # /home/me/jruby-9.1.15.0/bin/ri
6. ri Array # Nothing known about Array ⇐ ‼
7. ri --list-doc-dirs # /home/me/jruby-9.1.15.0/share/ri/2.3.0/system:/home/me/jruby-9.1.15.0/share/ri/2.3.0/site:/home/me/.rdoc
8. find /home/me/jruby-9.1.15.0/share/ri/2.3.0/system # No such file or directory
9. find /home/me/jruby-9.1.15.0/share/ri/2.3.0/site # No such file or directory
10. find /home/me/.rdoc # No such file or directory

Environment

• jruby -v # jruby 9.1.15.0 (2.3.3) 2017-12-07 929fde8 OpenJDK 64-Bit Server VM 9.0.1+11-Debian-1 on 9.0.1+11-Debian-1 +jit [linux-x86_64]
• uname -a # Linux debian 4.14.0-3-amd64 #1 SMP Debian 4.14.12-2 (2018-01-06) x86_64 GNU/Linux

[enebo]

@4r2r I am going to change the title of this issue a bit. I believe both rdoc and ri work fine but there are several issues:

1. we do not ship pre-generated rdoc data as part of distribution
2. Even if we did Array would not be included because rdoc cannot parse Java source files to extract documentation out of our native implementation (this is where Array comes from in MRI but from parsing C source)
3. We don't actually embed that documentation in our source.

So this is a valid issue but it underscores some other problems we have with providing a good 'ri' experience from our dist.

[headius]

What about rdoc-data? That provides doc dumps for various versions of Ruby, a gem install away.

cc @drbrain