The problem with configuration formats, is not syntax, or abstraction, it's the lack of consistent language server integration, it's problem when I can't lookup the definition for a key, the expected type, or quickly jump to definitions that clearly show which keys are available to configure.
To be frank, the clear problem with configuration format is that people have configurations so complex they probably should use something else.
Example: We are programming a backend for a blog. If we were to not use templates, but instead try to get that functionality via the webservice configuration we would have to "invent" some format that gives us the flexibility of templates within let's say a YAML file.
Needless to say that would be a horrible idea. Maybe I am being naive here, but I have yet to be convinced of the fact that it is really configuration formats that are the problem and not what people try to abuse them for. I have yet to work on a project where TOML wasn't enough for actual configuration.
Usually when I need something more complex than what can be done with TOML it is a sign that this needs to be handled differently. Via templates or with a database or making a special DSL-like script file. E.g. if you're using python nothing (except security considerations) stops you from allowing users to use a python file for configuration. If your configuration needs are really that complex, why not use a real programming language for it?
Two examples of complex user facing configurations I can think of are pretty trivial to implement:
- Decision tree, where you only need comparison operators. The leaves are a specified list of actions.
- actions list with macros (variables). You can be fancy and add some conventions for arrays.
Anything more that that should just be a programming language. And if the relationship is adversarial (saas), you should really think hard about needing something that complex.
