Configuration as code, but in a quirky language - how about no? I'm sure someone uses this, someone created this, and so it might seem like it's useful, but we have enough clownishness out there with yaml, json combined with js, json with eval and so on.
Create a framework in a normal language, but one which is very limited by design with regard to what is able to access - Skylark/Starlark is a good example[0], "limited Python" and use that. The rest works the same way, take an input in this language/framework, generate outputs.
Tried it[0], worked reasonably well. Be prepared for strong opposition from traditional “devops” folks (really just rebranded sysadmins) and boneheaded management “who don’t mind yaml” and will drag everyone down.
My employer (who I don’t speak for) used this for a long time. Im not normally particularly opinionated about tech choice, but I can very strongly say do not use jsonnet unless you enjoy adding an esoteric unsupported language to your job configs for no reason.
Not OP, but I can highly recommend just using the programming language you already use to make key-value map to and then converting that to JSON. That way you only have 1 syntax to worry about. In my case that’s Python (using dictionaries and json.dumps)
You could also try for a templating framework (like jinja2) but then you have 3 syntaxes colliding: the programming language you call the templating engine with (e.g. Python for jinja2) the templating language itself (e.g. jinja2) and then JSON as well.
This works for some languages but not others (some typed languages are particularly ill-suited to the problem of writing CLI tools to dump heterogenous dictionaries and/or objects with many optional fields)
I can definitely sympathize here - in every context, just straight JSON/YAML configuration seems never expressive enough, but the tooling created in response always seems to come with sharp edges.
Here are some of the things I appreciate about Jsonnet:
- It evals to JSON, so even though the semantics of the language are confusing, it is reasonably easy to eval and iterate on some Jsonnet until it emits what one is expecting - and after that, it's easy to create some validation tests so that regressions don't occur.
- It takes advantage of the fact that JSON is a lowest-common-denominator for many data serialization formats. YAML is technically a superset of JSON, so valid JSON is also valid YAML. Proto3 messages have a canonical JSON representation, so JSON can also adhere to protobuf schemas. This covers most "serialized data structure" use-cases I typically encounter (TOML and HCL are outliers, but many tools that accept those also accept equivalent JSON). This means that with a little bit of build-tool duct-taping, Jsonnet can be used to generate configurations for a wide variety of tooling.
- Jsonnet is itself a superset of JSON - so those more willing to write verbose JSON than learn Jsonnet can still write JSON that someone else can import/use elsewhere. Using Jsonnet does not preclude falling back to JSON.
- The tooling works well - installing the Jsonnet VSCode plugin brings in a code formatter that does an excellent job, and rules_jsonnet[0] provides good bazel integration, if that's your thing.
I'm excited about Jsonnet because now as long as other tool authors decide to consume JSON, I can more easily abstract away their verbosity without writing a purpose-built tool (looking at you, Kubernetes) without resorting to text templating (ahem Helm). Jsonnet might just be my "one JSON-generation language to rule them all"!
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Though if Starlark is your thing, do checkout out skycfg[1]
Why do you think jsonnet is quirky? It has pretty normal components overall: local bindings with lexical scope, imports, functions. Certainly more pedestrian / closer to most general purpose languages. The only strange bit may be thunks / lazy evaluation, but its definitely possible to opt out of relying on their behavior.
Create a framework in a normal language, but one which is very limited by design with regard to what is able to access - Skylark/Starlark is a good example[0], "limited Python" and use that. The rest works the same way, take an input in this language/framework, generate outputs.
[0] - https://bazel.build/rules/language