Author here! The issue here is that builds, and many other "just configuration" scenarios, are fundamentally complex. So many projects that start off as "just XML" or "just YAML" end up implementing their own half-baked programming language interepreter inside of their XML/YAML/JSON/whatever.
There is a reason why Bazel went with Python/Starlark, why Pulumi and CDK and friends are getting popular. Fundamentally, many of these use cases look surprisingly like programming languages: maybe not immediately, but certainly after you've dug in a bit. And having a properly designed purpose-build programming language (e.g. StarLark) or a flexible general purpose language (e.g. Typescript, Kotlin, Scala) does turn out to be the least-bad option
Examples:
* Github Actions Config Expressions https://docs.github.com/en/actions/writing-workflows/choosin...
* CloudFormation Functions https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGui...
* Helm Chart Templates https://helm.sh/docs/chart_best_practices/templates/
There is a reason why Bazel went with Python/Starlark, why Pulumi and CDK and friends are getting popular. Fundamentally, many of these use cases look surprisingly like programming languages: maybe not immediately, but certainly after you've dug in a bit. And having a properly designed purpose-build programming language (e.g. StarLark) or a flexible general purpose language (e.g. Typescript, Kotlin, Scala) does turn out to be the least-bad option