Many projects start out with just simple config files. But then they realize they need to do logic, and hack that into it. Then they realize they need more complex logic, and hack even more stuff in. And it's just a mess. It would have been much cleaner if they just started out with a scripting language.
Whether you should be putting logic in the config file is a different issue, but as long as people do it or have a need to do it, it's much better than crazy ad hoc solutions.
See these discussions on the issue: https://stackoverflow.com/questions/648246/at-what-point-doe... https://medium.com/@MrJamesFisher/configuration-files-suck-6...
But as soon as scripting is supported, it's impossible to write tools that process the config files and always work, especially with untrusted config files. You can't have both.
So the question is: can code be separated from config (like I've proposed above) (the code can still be inlined in the config file, as long as the "root" of the config file is declarative and the boundaries are well-defined)?
If no, which is more important: parseability or flexibility? It's a tradeoff.