Use Langium AST without exposing complete Langium AST/API.

[cdietrich]

Hi, we have the following usecase: we want to process the AST produced by Langium in the backend. But we dont want our backend code to (directly) depend on langium. So i guess we would need the following

• something like the generated ast.ts with the types and type guards
• something like the hydration/dehydration services to
  • serialize/deserialize the AST
  • restore an actual graph
• maybe a subset of utils like AstUtils.getContainerOfType

Did anybody already face a similar problem? how did you solve it?

Thanks in advance

[msujew]

I believe @sailingKieler had a similar issue in one of his projects. IIRC the "solution" was to copy and paste code from Langium.

Having a separate library for this would probably be nice. I'll think about this. You mentioned that depending on langium is unwanted. Would something like langium-utils be alright for you?

[sailingKieler]

To add on @msujew:

For my code generation demo in the browser (yes, a rather esoteric use case of executing the generator in the frontend) I had a related issue:
The DSL content is parsed by the LS in a worker, and the AST is serialized and transferred to the UI on each change, allowing to debug the generation live in the browser.
Because of the small self-contained example inputs, the hydration can be quick and dirty like this:
https://github.com/TypeFox/langium-in-browser-codegen-example/blob/main/src/generator/generator.ts#L82-L93
(don't know whether that's still possible with more recent langium versions)

[montymxb]

I wrote something up last year to help a bit with this without depending on Langium directly, https://www.npmjs.com/package/langium-ast-helper (repo as well). The focus is on supporting data viz applications, but it does provide de-serialization & graph conversion capabilities. Although not much else, as it was intended to be pretty slim. The use case was making it easier to build external tooling that could consume and project Langium ASTs generally.