FWIW, here's a repo of ANTLR grammars: https://github.com/antlr/grammars-v4

Many of them are incomplete, but it gives a good idea of how the grammar looks for ANTLR.

I used the ANTLR grammar for parsing CSS in DiffLens (https://github.com/marketplace/difflens). DiffLens uses the typescript compiler itself to parse TS and JS.

I've also used Roslyn to parse C# (and F#). I wonder if the ruby compiler itself exposes a parser.