Dart closing labels: support for `dart/textDocument/publishClosingLabels` from LSP

[bogdanbws]

Would it be possible to get Closing labels in .dart files for Widgets, like in the attached screenshot?

[notpeter]

This is a dart-specific LSP extension which can be enabled via initialization_options:

  "lsp": {
    "dart": {
      "initialization_options": {
        "closingLabels": true
      }
    }
  }

But is not supported by zed so will just log error messages like this:

2025-04-22T16:12:10-04:00 INFO  [lsp] Language server with id 7 sent unhandled notification dart/textDocument/publishClosingLabels:
{
  "labels": [],
  "uri": "file:///Users/peter/zcode/dart/a.dart"
}

Thanks for reporting.

[bogdanbws]

I see, thank you for the reply!

[bogdanbws]

@notpeter Since this issue hasn't gotten any attention for a while, I would like to try and contribute to the editor and the extension in order to solve this issue. From your initial comment, I understand that this isn't a simple fix and requires adding support for custom LSP notification handlers. Can you please read through my initial thoughts and point me in the right direction?

If I understand things correctly, the issue is that the LSP emits custom notifications and the Zed editor isn't parsing them, so I am thinking of reusing the inlay hint implementation for the closing labels. However, since it's Dart language specific, I am guessing a generic handler for custom LSP notifications needs to be implemented in the core Zed project, which forwards the result to any matching extensions. After getting this done, inside the Dart extension project I need to parse the custom notification and transform it into an inlay hint that can be rendered. This would only be possible after the inlay hints are made available in the bridge between the core project and the extension project.

Does this make sense or am I misunderstanding the separation of concerns here? Also, is reusing the inlay hint implementation a good idea or are you and the team looking into using some other decorative API for this functionality?