How to detect multi-line comments without closing?

[durianwaffle]

Hi Langium community,

I am using comment token to check if current cursor is in multi-line comment.
But the problem is if the comment is not closed, it will not have the comment token.

May I know if there are existing services to detect if current cursor location is in multi-line comment?

[wa8f7192]

Hi,

To addon to the comment, attaching examples here

Works for these examples

/*
<user's cursor>
*/

/* <user's cursor>
*/

// Single line comment works as well <user's cursor>

Doesn't work for this

/* <user's cursor>

Our current code

// Code to detect if the cursor position is at a comment
export const positionIsAtComment = (document: LangiumDocument<AstNode>, position: Position): boolean => {
    const documentCstNode = document.parseResult.value.$cstNode;
    if (!documentCstNode) {
        return false;
    }
    const offset = document.textDocument.offsetAt(position);
    const cstNode = CstUtils.findDeclarationNodeAtOffset(documentCstNode, offset);
    

    if (cstNode?.tokenType) {
        return cstNode.tokenType.name.toUpperCase().includes('COMMENT');
    }
    return false;
}

These are the rules used for terminal for us

hidden terminal WS: /\s+/;
terminal ID: /[_a-zA-Z][\w_]*/;
terminal NUMBER returns number: /[0-9]+(\.[0-9]+)?([eE][+-]?[0-9]+)?/;
hidden terminal ML_COMMENT: /(\/\*[\s\S]*?\*\/)/;
hidden terminal ML_COMMENT1: '(*' -> '*)';
hidden terminal SL_COMMENT: /\/\/[^\n\r]*/;

[msujew]

Hey @durianwaffle, @wa8f7192,

you should be able to do something like that:

hidden terminal ML_COMMENT_INCOMPLETE: /(\/\*[\s\S]*)/;

and move that behind the existing ML_COMMENT terminal. That way you don't accidentally hide the existing comment terminal.

[durianwaffle]

Thanks a lot! It works!

[durianwaffle]

But I found some issues for nested comments:

[msujew]

You cannot create nested comments with regex, as that would require recursion (or at least a stack). You need to write the PATTERN function for the token type yourself. See the TokenBuilder for more info.