To synthesis my comment down (because it's easier once I've written it once, poorly):
The complexity you see in Bazel/Buck/Pants build files may seem like a result of their decision to use a programming language. That's a red herring. That complexity is fundamental to the problems people need to solve to build software. If you remove the ability to solve it in your build system the complexity will move to other systems.
Wrappers, CI, whatever. The complexity is just the problem space rather than a result of bad tooling.
> If you remove the ability to solve it in your build system the complexity will move to other systems.
Adding to this: I think one of the main limitations of purely declarative (e.g. YAML-based) configurations is that a declarative DSL (as opposed to an imperative DSL) means you (only) get to use config options the inventors of the config language have thought of and implemented (i.e. "defined"). You cannot put into words things that require vocabulary that doesn't exist in your language.
Meanwhile, an imperative language gives you the ability to define on your own what you would like the machine to do.
As an example, consider Gitlab CI configs (YAML-based) or Ansible playbooks. In both cases, once you hit the boundaries of the DSL spec (which, in my experience, typically happens on day one) you can't do anything other than 1) give up or 2) leave the realms of the DSL and as you say,
Well thought and I can imagine this can be further differentiated. E.g. what is considered boundaries or limits in a declarative way also work as guardrails. So while it could be possible to hit actual limits on day one, there is often more than only two options to go on. Declarative for me often appears easier to find the correct one or to correctly know that that system is not designed to do that.
The other differentiation I think is worth on the following part, also which I'd liked a lot btw:
> move [the complexity] to other systems
which stemmed from:
> If you remove the ability to solve it in your build system the complexity will move to other systems.
I think it is even _more_ beneficial to consider that this does not start at the build system:
If you don't have and don't add the ability at development (make it a property of the project), the complexity will continue to _increase_ each time you move it into other systems after it (build, version control, CI, ... etc.).
To add to everyone else, please don't use YAML. Starlark is great _precisely_ because it is a readable, well known (nearly Python) language that is limited at the same time (no unbounded for loops, no way to do non-deterministic things like get the current time or `random()`).
Take a look at Apache Aurora [1] if you want some inspiration on how to mold python into a config language. I used this system for a few years and mainly agree with the person you're replying to – having a proper programming language to define config is a very nice feature that I miss.
one of the benefits of starlark (unlike python): "Starlark is suitable for use in highly parallel applications. An application may invoke the Starlark interpreter concurrently from many threads, without the possibility of a data race, because shared data structures become immutable due to freezing." from https://github.com/bazelbuild/starlark/blob/master/spec.md - it's not python, you can't do recursion (!) and it's more limited (you can't read a file in bazel, and parse it, you have to make this operation into the graph somehow)
