Yeah a nice Rust or Go-based implementation of Asciidoc would be fantastic. Having to deal with Ruby and Gems is not fun.
That's a mountain of work though and even if there is a spec, at this point it's complex enough and the Ruby implementation is enough of a de facto spec that I'm doubtful you'll ever make it past "this behaves differently to Asciidoctor" territory.
Btw a more recent alternative is https://github.com/jgm/djot which actually does have multiple implementations and looks like a way better option than Markdown, but maybe not as powerful as Asciidoctor still. I haven't tried it.
That's a mountain of work though and even if there is a spec, at this point it's complex enough and the Ruby implementation is enough of a de facto spec that I'm doubtful you'll ever make it past "this behaves differently to Asciidoctor" territory.
Btw a more recent alternative is https://github.com/jgm/djot which actually does have multiple implementations and looks like a way better option than Markdown, but maybe not as powerful as Asciidoctor still. I haven't tried it.