Getting access to AST-Infos via langium framewokr from right-click in IDE editor and emit command to other webview

[jhln]

Hello community,

I'm trying langium to customize a DSL-interaction in VS Code.
The idea would be in the case of the greeting example to right-click the name in a Greeting and choose a listed command in the pop-up to send infos of the current AST-Node or it's parent or sth. like that to another webview.

I added the messanger, works,
the command in the popup-menu after right-clicking, and have now the position.

But I need to resolve this position to the AST - and I guess via a service in the language server of that DSL.
But here I'm a bit stuck, and wanted to ask kindly for some instructions, what to plug where?

I found this blogpost @sailingKieler about source maps in the generation phase:
https://www.typefox.io/blog/code-generation-for-langium-based-dsls-3/
But it also mentioned, that the positions are already there from the concrete syntax parsing

Thanks in advance!

[msujew]

Hey @jhln,

as you correctly pointed out, all the positions are stored on the CST nodes of every AST element. You can simply use node.$cstNode?.range to get the range of any AST element. That's for example how our LSP services work. See as an example:

langium/packages/langium/src/lsp/definition-provider.ts

Lines 68 to 79 in 58ce261

	protected collectLocationLinks(sourceCstNode: CstNode, _params: DefinitionParams): MaybePromise<LocationLink[] | undefined> {
	const goToLink = this.findLink(sourceCstNode);
	if (goToLink) {
	return [LocationLink.create(
	goToLink.targetDocument.textDocument.uri,
	(goToLink.target.astNode.$cstNode ?? goToLink.target).range,
	goToLink.target.range,
	goToLink.source.range
	)];
	}
	return undefined;
	}

[cdietrich]

you can extend AbstractExecuteCommandHandler and register it as lsp.ExecuteCommandHandler (shared module)

[msujew]

...but maybe I don't see, how the language server resolves the node already/underneath/before, though - where does this happen in your example?

Perhaps you should take a look at the whole file. It does the whole transformation from Position -> CstNode -> AstNode -> Reference Resolving -> AstNode -> CstNode -> Position in order to perform the "go to definition" request.

https://github.com/eclipse-langium/langium/blob/58ce261b9c5b0340552110990154caf3e2545183/packages/langium/src/lsp/definition-provider.ts

[cdietrich]

or you extend the protocol with your own messages (connection.onRequest in language/main.ts) (see e.g. packages/langium-vscode/src/language-server/main.ts)

[jhln]

...but maybe I don't see, how the language server resolves the node already/underneath/before, though - where does this happen in your example?

Perhaps you should take a look at the whole file. It does the whole transformation from Position -> CstNode -> AstNode -> Reference Resolving -> AstNode -> CstNode -> Position in order to perform the "go to definition" request.

https://github.com/eclipse-langium/langium/blob/58ce261b9c5b0340552110990154caf3e2545183/packages/langium/src/lsp/definition-provider.ts

oh sure, I missed the position in the DefinitionParams type..

thanks a lot!

[jhln]

or you extend the protocol with your own messages (connection.onRequest in language/main.ts) (see e.g. packages/langium-vscode/src/language-server/main.ts)

thanks a lot, I will try this out!