What's the right way to insert code after validation?

[jiashengguo]

For example, for the DomainModel, after user input

entity Post{
many comments: Comment
}

Instead of showing the error of not finding a Comment, I would like to generate a Comment entity for the user if he hasn't done so.

How should I achieve that?

[msujew]

Hey @jiashengguo,

to not interrupt the normal document lifecycle, it would make sense to basically do the following:

1. Register a onBuildPhase listener on your document builder instance for the Validated state (i.e. so that the callback runs after a document has been validated)
2. Look in the references of your document for unresolved references (i.e. those reference with their error not being undefined)
3. Create a new workspace edit for all missing elements and send them to the client using the workspace/applyEdit LSP endpoint available on the services.lsp.Connection object.

Note that I would not recommend building such an automated solution due to false positives. Let's take the following for example:

entity Post {
  many comments: Commet // <- Note the missing `n` character
}
entity Comment { // <- This is what the user wanted to reference
  ...
}
entity Commet { // <- This will be generated automatically instead
  ...
}

Once the user writes an invalid reference, it will automatically create a new entity in the text which might not be what the user wants, especially if it's only due to a typo. You should let the user decide whether they want to create an entity for that instead using code actions. You can see an example how to create code actions on linking errors here.

[jiashengguo]

@msujew Thanks for the quick response and reminder! Actually, I just use that simple example to illustrate that I need to insert some code after the validation phase. I totally agree with you that it makes more sense to use code action for that case.