Just because borgcfg is painful (?) and YAML is a better option for the public, doesn't mean we can't continue and improve on YAML with more limited expression syntax. Terraform/HCL is often annoying because it doesn't give users tools like easy function declarations for re-use. You get one re-use abstraction: create a module, which is heavy-weight - needs a new directory, "provider version" declarations, a lot of boilerplate per input and output. In return this means the amount of creative shenanigans one needs to understand is typically pretty low.

Interested to hear more about this. Care to elaborate more? Maybe there are already articles written about this?

I've spent many, many, many years working with YAML at $DAYJOB. YAML is just a really bad choice for configuration files that are longer than a handful of lines.

The fact that YAML encourages you to never put double-quotes around strings means that (based on my experience at $DAYJOB) one gets turbofucked by YAML mangling input by converting something that was intended to be a string into another datatype at least once a year. On top of that, the whitespace-sensitive mode makes long documents extremely easy to get lost in, and hard to figure out how to correctly edit. On top of that, the fact that the default mode of operation for every YAML parser I'm aware of emits YAML in the whitespace-sensitive mode means that approximately zero of the YAML you will ever encounter is written in the (more sane) whitespace-insensitive mode. [0]

It may be that bcl is even worse than YAML. I don't know, as I've never worked with bcl. YAML might be manna from heaven in comparison... but that doesn't mean that it's actually good.

[0] And adding to the mess is the fact that there are certain constructions (like '|') that you can't use in the whitespace-insensitive mode... so some config files simply can't be straightforwardly expressed in the other mode. "Good" job there, YAML standard authors.