Find where function is defined

I'm building a docs generator for Jsonnet at [sh0rez/docsonnet](https://github.com/sh0rez/docsonnet).

It builds a godoc-style page, and I would like to copy the behaviour where you click on a signature and are redirected to the respective source code on github.com.

While I can quite easily get the filename by passing `std.thisFile` to my library, the actual line in the source file is harder.

Is there a recommended / good way to approach this problem?