How to validate invalid hidden terminals?

[JohannesMeierSE]

In my language, two different kinds of comments are supported (e.g. // comment and # comment), i.e. there are two different hidden terminal rules for comments. While both kinds of comments are valid for most files, there are some files (identified by their file extension), which support only one kind of comments, while the other kind is forbidden.

How to realize that? Ideally, the user would get a validation hint with a quick-fix to use the other kind of comments instead.

I see the following approaches:

• Approach 1: Convert the single-language project to a multi-language project with different sets of hidden terminal rules in the grammars. Drawback: Switch to a multi-language set-up is a lot of overhead for a detail, no validation check and therefore no quick-fix
• Approach 2: Support both hidden terminal rules in the grammar. During validation, traverse CST nodes and check for the kinds of comments. Drawback: probably bad performance (?)

[cdietrich]

3. Iterate the cst leaves, search for gaps . Request gap content from TextDocument

[msujew]

As Christian points out, we still add the hidden terminals to the CST, so you should be able to see them in there.

[JohannesMeierSE]

Yes, thanks, I hoped for a trick in order not to traverse the CST so much.