Alternative Ruby Implementations

[rkh]

It would be great to support alternative Ruby implementations. But we're not compatible at the moment.

A couple of modern Ruby features we use:
• Better Unicode support (including relying on Ruby's Unicode normalization). This was introduced in Ruby 2.5, so it should work just fine. This could possibly also be backfilled.
• Pattern matching (experimental support was added in Ruby 2.7, official support in Ruby 3.0)
• Endless method definitions (these could be removed, but only if all other issues are addressed).
• Exception handling without begin (Ruby 2.6, these could also be removed, but only if all other issues are addressed).
• Assumes full separation of keyword and positional arguments (Ruby 2.7).
• Hash#slice (2.5?), Hash#except (3.0)
• Argument forwarding (2.7?), including leading arguments (3.0).
• Hash#transform_keys with hash argument (3.0, could be removed, but only if all other issues are addressed).
• NilClass#=~ (2.6)
• Endless (2.6) and beginless (2.7) range.
• Warning categories (3.0 – limited use, could be made conditional)
• Symbol#name (3.0)
• Numbered parameters (2.7)
• Enumerable#filter_map (2.7 – limited use, could be eliminated).

This list may be incomplete, as I'm only testing against Ruby 3.0.

Current Status

Compatiblity	JRuby	Truffle Ruby
Ruby 2.5	compatible	compatible
Ruby 2.6	jruby/jruby#6161	compatible
Ruby 2.7	jruby/jruby#6464	oracle/truffleruby#2004
Ruby 3.0	–	–