I've been working on extending ZeroBrane Studio (the IDE mentioned in the google groups discussion you referenced) and its debugger and has posted instructions on how to debug OpenResty Lua scripts with it: http://notebook.kulchenko.com/zerobrane/debugging-openresty-....
It's an early work, but you can set breakpoints, step through the code, run ngx commands remotely, inspect stack/variables, and do all the things you'd expect from an interactive debugger. I included a screenshot in the blog post.
I'm interested in getting it to work with moonscript/lapis as well, but ran into issues with mapping source code information between moonscript and lua from the debugger.
It's an early work, but you can set breakpoints, step through the code, run ngx commands remotely, inspect stack/variables, and do all the things you'd expect from an interactive debugger. I included a screenshot in the blog post.
I'm interested in getting it to work with moonscript/lapis as well, but ran into issues with mapping source code information between moonscript and lua from the debugger.