How to implement nested languages?

[trusktr]

For example, let's say I'm using TypeScript, and I have this and it is working and returning some value:

const value = myTemplateTag`
  [foo] = bar
  foo
`()

console.log(value)

I want to add custom type checking inside the content of the string, but everything else on the outside will be handled by TypeScript.

How can we achieve this with Langium?

Maybe we can extend the TypeScript language service so that any time we encounter a template tag of a certain name (or from a certain module, with any name), then we get the string content, and we can pass that to Langium, get the results, then map those results back to TypeScript diagnostics?

Or something else? Thoughts?

[msujew]

Hey @trusktr,

Something like this could work yes. See this thread on how this can be accomplished.

I don't think its necessary to extend the TypeScript language service. You just need to register the respective callbacks in the vscode.languages API object.