Says MessageActionItem additionalPropertiesSupport is true, but not seeing the properties

[tjpalmer]

For MessageActionItem, LSP and lsp4j support the additionalPropertiesSupport indicator.

https://github.com/eclipse/lsp4j/blob/c0eaa1837900fcac5f0a991b3a33a26c6ed160b6/org.eclipse.lsp4j/src/main/java/org/eclipse/lsp4j/Protocol.xtend#L1773

I'm trying to use it to disambiguate choices, and I've subclassed MessageActionItem for my outgoing items as seen in this trace:

[Trace - 06:40:43 AM] Sending request 'window/showMessageRequest - (2)'
Params: {
  "actions": [
    {
      "value": "",
      "title": "notes/"
    },
    {
      "value": "yodel",
      "title": "yodel/"
    },
    {
      "value": "yodel/monkey",
      "title": "monkey/"
    },
    {
      "value": "yodel/monkey/yodel",
      "title": "yodel/"
    }
  ],
  "type": 2,
  "message": "Choose a folder."
}

[Trace - 06:40:46 AM] Received response 'window/showMessageRequest - (2)' in 2161ms
Result: {
  "title": "yodel/"
}

I expect to see the "value" field back as well. And I'm not sure if vscode isn't sending it (in which case maybe my fault) or if lsp4j is converting to MessageActionItem and then logging the equivalent json. And I haven't found a way to customize the return type in lsp4j.

And vscode seems to claim to support this feature based on earlier in the trace logs:

      "showMessage": {
        "messageActionItem": {
          "additionalPropertiesSupport": true
        }
      },

Is it possible this issue is in lsp4j, and if so, is there a way to get back the additional properties?

[tjpalmer]

One of my questions is that I'm unsure if the "Result" trace above is the pure response or if it's a re-jsonification of the created MessageActionItem object.

[pisv]

LSP4J does not (cannot) support additional properties for MessageActionItem OOTB. By default, GSON deserialization will just create an instance of MessageActionItem and not of your subclass, so all of the additional properties get lost.

I think you need to use one of createIoLauncher methods in org.eclipse.lsp4j.jsonrpc.Launcher that allow you to get access to a GsonBuilder and then register a type adapter for MessageActionItem that would return an instance of your subclass. See https://futurestud.io/tutorials/gson-advanced-custom-deserialization-basics for more information on this topic.

[tjpalmer]

🙏 Thanks much for the tips! I'll look that direction.

One other thing I tried doing was making my own custom method to send the same message to the client, but then it complained I had two methods with the same message type registered. Not sure if there's any way lsp4j could allow that and coordinate the response.

[pisv]

One other thing I tried doing was making my own custom method to send the same message to the client, but then it complained I had two methods with the same message type registered. Not sure if there's any way lsp4j could allow that and coordinate the response.

I don't think it is supported.

[KamasamaK]

This was an unfortunate choice for LSP. I opened microsoft/language-server-protocol#1471 but I'm not sure when it will be addressed.