How to handle multi-languages language servers

[Yokozuna59]

Hi there,

In our project, we have different languages/diagrams have the same document, so we overridden ServiceRegistry and register each language and it services and used a detector to check what language it is.
But it appears that the language server doesn't work anymore, shouldn't it switch between language servers when it identifies the keyword? It does that for the parser and other services.

• Using the diagram service itself:

  

• Using the wrapper service that contains all diagrams:

  

---

Is this an issue? Or we're messing something? Should I create a clone of the project?

[msujew]

Do you get any error from the language server when you request completions? Does it generate diagnostics as expected? The first issue to rule out would be to identify whether the language service selector/registry is at fault or whether the logic doesn't play nicely with the completion provider.

[Yokozuna59]

Do you get any error from the language server when you request completions?

No.

Does it generate diagnostics as expected?

I'm not really sure how to check that.

[msujew]

Just type in something invalid, such as info ßßß (hopefully that is actually invalid data). It should complain about a syntax error.

[Yokozuna59]

Other services works fine expect completions of the language server.

[msujew]

Ok that seems to rule out the issue that it can't find the info service. Do you have a reproducible example I can take a look at? I'm curious what goes wrong in the completion provider.

[Yokozuna59]

Sure, here is it: https://github.com/Yokozuna59/multi-lang-example. It took me more time to add related files only.

To build the playground:

pnpm --filter playground build

And to start the editor:

pnpm --filter playground dev

[Yokozuna59]

The weird part is that when running the languages as a VSCode extension, it doesn't run any services, not even the parser.
But if I used the individual language service, it would only enable the parser when the document is saved. It doesn't show real-time error highlighting or autocomplete for keywords.

[Yokozuna59]

@msujew Done, pushed to master.

I'm having a bit of trouble building/debugging the repo you linked.

Can you please share them?

[msujew]

Sure, seems like the import here doesn't exist.

[msujew]

The vscode extension doesn't work due to an id mismatch, see here.

[msujew]

Your service registry is missing an override for the all getter:

override get all(): LangiumServices[] {
    return Object.values(this.services);
}

The language server tries to identify whether it needs to register a completion provider based on the info that any service has a completion provider at all. It does this by looking through the all property. In your case, it always stays empty, so no language services are registered.

I've investigated the completion issue a bit and saw that the completion parser arrives at an unexpected state:

The added \n token doesn't appear in the input, but gets added by the lexer. As mentioned before, completion in whitespace-sensitive languages doesn't work well currently. PRs improving this are appreciated though.

[Yokozuna59]

Sure, seems like the import here doesn't exist.

I've it locally, it was for overriding services to add LSP services, but I didn't use it yet so I didn't push it.

The vscode extension doesn't work due to an id mismatch, see here.

The id is indented, I used this id to not interfere with existing extensions that uses this id.
But I guess I didn't change these:

https://github.com/Yokozuna59/multi-lang-example/blob/d71f444e83c2e91ecf82c77d6ddba0687cf1b5eb/packages/mermaid-vscode/src/extension.ts#L48-L57

[Yokozuna59]

Your service registry is missing an override for the all getter:

override get all(): LangiumServices[] {
    return Object.values(this.services);
}

The language server tries to identify whether it needs to register a completion provider based on the info that any service has a completion provider at all. It does this by looking through the all property. In your case, it always stays empty, so no language services are registered.

I see, thanks! It's working as expected. Except showData from pie, maybe it's because of the whitespace-sensitive as you stated.

I've investigated the completion issue a bit and saw that the completion parser arrives at an unexpected state:

The added \n token doesn't appear in the input, but gets added by the lexer. As mentioned before, completion in whitespace-sensitive languages doesn't work well currently. PRs improving this are appreciated though.

Oh, I see. I don't really know how to resolve such error. Would using EOF would resolve such error?

[Yokozuna59]

The completions is currently working in the vscode extension, but the parser doesn't.
And it keeps throwing error:

Error:  RangeError: Maximum call stack size exceeded
    at Object.get (packages/mermaid-vscode/dist/main.cjs:65:57744)
    at e8.documents (packages/mermaid-vscode/dist/main.cjs:203:1526)
    at e8.getServices (packages/mermaid-vscode/dist/main.cjs:203:1722)
    at packages/mermaid-vscode/dist/main.cjs:88:20796
    at get textDocument [as textDocument] (packages/mermaid-vscode/dist/main.cjs:88:20164)
    at e8.getServices (packages/mermaid-vscode/dist/main.cjs:203:1848)
    at packages/mermaid-vscode/dist/main.cjs:88:20796
    at get textDocument [as textDocument] (packages/mermaid-vscode/dist/main.cjs:88:20164)
    at e8.getServices (packages/mermaid-vscode/dist/main.cjs:203:1848)
    at packages/mermaid-vscode/dist/main.cjs:88:20796

The browser works fine though.

[msujew]

I see. You probably need to override the createTextDocumentGetter method to get the type from the text instead of using the service registry.