I used TOML for complex configuration and I am quite happy with it. However I often saw people who complained with it, and most of the complains afaik are of t

I used TOML for complex configuration and I am quite happy with it. However I often saw people who complained with it, and most of the complains afaik are of the nature: "This extremely complex use case, that I could as well just write in an interpreted language isn't supported by TOML". If your configuration is so crazy it needs more than any configuration language offers, just use a scripting language instead. I have seen lua or python files act as configuration and there is nothing wrong with that.