Why? If they can’t learn HCL, they’re not going to be a successful developer.

If your argument is instead that they shouldn’t learn infrastructure, then the point is moot because that applies equally to every choice (knowing how to indent YAML doesn’t mean they know what to write). That’s also wrong as an absolute position but for different reasons.

You don't see my point. The ideal solution would be something that can be learned easily by both the dev and infra side without having to boil the ocean on one side or the other. Something like protobuf was mentioned above which is a better idea than hcl imho

I understand but do not agree with your point. I think two things are being conflated: the difficulty of learning HCL itself and the domain complexity of what almost everyone is learning HCL to do. I’ve seen people bounce off of Terraform and make lengthy rants about how HCL is hard, write thousands of lines of code in their preferred Real Programming Language™, and only eventually realize that the problem was that they thought they were learning one thing (IaC) but were actually learning two things at the same time (IaC and AWS/GCP/etc.) without taking time to formalize their understanding of both.

I have no objections to protobufs, but I think that once you’re past a basic level of improvements over YAML (real typing, no magic, good validation and non-corrupting formatters) this matters less than managing the domain complexity. YAML is a bad choice for anything but text documents read by humans because it requires you to know how its magic works to avoid correct inputs producing unexpected outputs (Norway, string/float confusion, punctuation in string values, etc.) and every tool has to invent conventions for templating, flow control, etc. I think HCL is better across the board but am not dogmatic about it - I just want to avoid spending more time out of people’s lives where they realize that they just spent two hours chasing an extra space or not quoting the one value in a list which absolutely must be quoted to avoid misinterpretation.

Terraform is good overall but HCL just isn't a very good language.

Given that its main purpose is to describe objects of various types, its facilities for describing types are pretty weak and its facilities for describing data are oddly inconsistent. Its features for loops and conditionals are weak and ad-hoc compared with a regular programming language. Identifier scope / imports are a disaster and defining a function is woeful.

Some of this is influenced by Terraform's problem domain but most of it isn't required by that (if it was required, people wouldn't have such an easy time doing their Terraform in python/go/rust).

Despite this, Terraform is overall good. But there's a reason there's a small industry of alternatives to HCL.

I can't understand how somebody would learn maintain a config written in protobuf. At least hcl is actually readable.

Say what? Protobuf may be type safe but it is far from a configuration language, can you even refer to variables or do loops. Unless you are thinking about serializing it with builders in code, which takes away the benefit of declarative configuration. It's also not readable without tooling. As parent said, this really sounds like refusal to learn something new.

In what universe is protobuf simple? Also what do you even mean by protobuf here?

The actual format is binary and I'm not expecting people to pass around binary blobs that describe their deployment configuration.

to serialize it, you're writing code in some language... then what? you just want deployment as code? because that seems like a separate paradigm.