JRuby support

[headius]

This gem is unusable on anything but CRuby mostly because it uses the following CRuby-specific features:

lib/error_highlight/base.rb  (4 usages found)
    59           RubyVM::AbstractSyntaxTree.of(loc, keep_script_lines: true)
    70     when RubyVM::AbstractSyntaxTree::Node, Prism::Node
    93     node_id = RubyVM::AbstractSyntaxTree.node_id_for_backtrace_location(location)

We could fix this for JRuby in one of two ways:

• Switch to the Prism gem where possible. I'm not sure if it can help us get a specific AST node from a backtrace element without reparsing, though. cc @kddnewton
• Use JRuby-specific methods to access similar internal code structures.

It would be nice if JRuby users could benefit from the features of this gem.

[kddnewton]

Yeah, you'd need to respect something akin to RubyVM.keep_script_lines. Honestly to truly solve this in a portable way, we'd need something like https://bugs.ruby-lang.org/issues/21795.

In terms of using JRuby-specific features, you would need to leverage the node_id that Prism provides. Right now JRuby is ignoring it I think. But we would need an equivalent of RubyVM::AbstractSyntaxTree.node_id_for_backtrace_location(location), where location is a Thread::Backtrace::Location object.

[mame]

This gem already supports the Prism gem. The missing piece is a way to retrieve the corresponding AST node from a Thread::Backtrace::Location in JRuby.

If such a JRuby-specific API is already available and reasonably stable, I would be happy to support it in error_highlight.

I agree with @kddnewton that the ideal long-term solution is reaching a consensus on https://bugs.ruby-lang.org/issues/21795 and having JRuby implement it, though I expect that will take time.