This is a toy project.
In this case I wanted to learn more about procedural macro functions. I was too lazy to come up with a case and a DSL for it, so I thought "well, there are already plenty of languages out there, say, shell script". Thus, an idea for compile time shell scripts was born. Something of such sort could maybe potentially be used as an alternative to build scripts.
I will leave out question on say, portability, and abusability.