MessageActionItem should permit additional fields

[nemethf]

Although the LSP specification does not define it explicitly, from the definition of ShowMessageRequestClientCapabilities it follows that MessageActionItem can have additional fields:

	messageActionItem?: {
		/**
		 * Whether the client supports additional attributes which
		 * are preserved and sent back to the server in the
		 * request's response.
		 */
		additionalPropertiesSupport?: boolean;
	};

However, lsprotocol does not permit this:

    print(types.MessageActionItem(title="title", asdf="asdf"))
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: MessageActionItem.__init__() got an unexpected keyword argument 'asdf'

(See the pygls issue)

Thanks

[debonte]

I filed an issue on https://github.com/microsoft/language-server-protocol asking that they make this behavior of MessageActionItem clear in the LSP meta model

[debonte]

Dirk is planning to make a protocol change so our generator will understand that MessageActionItem can have additional fields -- microsoft/language-server-protocol#2148 (comment)