It's not clear from `metaModel.json` that `MessageActionItem` can contain arbitrary additional fields

[debonte]

The generator in https://github.com/microsoft/lsprotocol uses metaModel.json as the source of truth about the LSP protocol.

While the docs for ClientShowMessageActionItemOptions.additionalPropertiesSupport indicate that MessageActionItem objects can contain arbitrary additional attributes beyond what is shown in the spec, the description of MessageActionItem itself doesn't indicate this:

		{
			"name": "MessageActionItem",
			"properties": [
				{
					"name": "title",
					"type": {
						"kind": "base",
						"name": "string"
					},
					"documentation": "A short title like 'Retry', 'Open Log' etc."
				}
			]
		},

I think it would be more standard to have an optional data field of type LSPAny, like on the Diagnostic object.

Is there any way that we can make this aspect of MessageActionItem clear in the json spec so tools that consume metaModel.json can support it correctly?

Related:

• MessageActionItem should permit additional fields lsprotocol#411
• Additional properites of MessageActionItem openlawlibrary/pygls#518

[dbaeumer]

I agree on the data filed. The reason it is that way is that MessageActionItems are available since a very long time and that was added for backwards compatibility since servers added additional properties :-(.

All I can think of right now is to add a property supportCustomProperties to these types.

[dbaeumer]

Would that work?

[debonte]

Yes, that should work, thanks!

Two questions:

1. Are you aware of other types that behave this way, or is it just MessageActionItem?
2. Am I correct in assuming that this supportCustomProperties property would only be intended for use as a hack on legacy types, whereas newer types would lean towards using a data field?