Autocompletion for sentences with validation error

[durianwaffle]

I am wondering if I have grammar error at other lines, how to show the autocompletion as usual for current line?
Now it will break down and show the default autocompletion items in completionFor.
And why the autocompletion items after typing ( is different from typing ctrl+space within ()?

Background.

• I implemented my own getCompletion in completion provider, and handled autocompletion for triggerChar === '(' there by passing an empty completion list and only show function block instances.
• I used completionFor for default autocompletion which will handle ctrl+space within ().

Question:

• CompletionFor has properties: context: CompletionContext, next: NextFeature, acceptor: CompletionAcceptor while getCompletion has properties: document: LangiumDocument<AstNode>, params: CompletionParams has no accepter. How to show the same autocompletion lists using the two functions? Now if I type ctrl+space in '()' I will see RangeError: Maximum call stack size exceeded error.
• How to show auto completion list as usual for current line if there is grammar mistakes in other lines?
• How to use markdown in the documentation of completion items? Can I highlight different parameters when I type at different positions in function ()? e.g. item.documentation = 'the **documentation** of this function block...' doesn't work. How to make it work?

[msujew]

Hey @durianwaffle,

How to show the same autocompletion lists using the two functions?

I'm not entirely sure what you mean by that. getCompletion is the entry point into the completion algorithm - since we only get the parameters from the language client, it's all that we have to perform the completion. completionFor is way deeper into the algorithm, at a point where we've already identified what our next grammar element will be - both of these methods serve entirely different purposes.

Now if I type ctrl+space in '()' I will see RangeError: Maximum call stack size exceeded error.

Does that happen when using the default completion provider or in your own implementation?

How to show auto completion list as usual for current line if there is grammar mistakes in other lines?

Assuming the error recovery works as expected, syntax errors in other lines of the file should not influence completion. However, if the error is unrecoverable, that might lead to issues. You can probably override the findFeaturesAt method to get a better start position, but that is pretty non-trivial (which is why it isn't implemented that way yet in Langium).

How to use markdown in the documentation of completion items?

In order to use markdown in the documentation, you need to use the MarkupContent interface. See our implementation in the completion provider as a reference:

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

Lines 478 to 487 in b2c40e3

	protected getReferenceDocumentation(nodeDescription: AstNodeDescription): MarkupContent | string | undefined {
	if (!nodeDescription.node) {
	return undefined;
	}
	const documentationText = this.documentationProvider.getDocumentation(nodeDescription.node);
	if (!documentationText) {
	return undefined;
	}
	return { kind: 'markdown', value: documentationText };
	}

Note that in general, completion is probably the most complicated (from a code/logic perspective) feature in Langium. It's incredibly hard to get it right for all situtations.

[durianwaffle]

And I am wondering if I have a grammar with 3 keywords:

1. A
2. AB
3. B

Then it causes false validation error under keyword AB because langium is not greedy and it processed keyword AB as two separate keywords A and B but there is not keyword_a then keyword_b grammar in my langium grammar.

How to fix this issue?

[cdietrich]

i dont think you can set it within additional edits

[durianwaffle]

I see. Do you have any idea where can I set it?

[cdietrich]

in the snippet itself

acceptor(context, {
      label: "my snippet",
      kind: CompletionItemKind.Snippet,
      insertText: "some keyword  $1 {\n\t$0\n}", // $1 will be the first cursor, $0 the final
      insertTextFormat: InsertTextFormat.Snippet,
      detail: "xxx",
      documentation: "yyyy",
      sortText: "3",
    })

[durianwaffle]

Thank you @cdietrich ! It helps a lot