How to respond with InitializeError on Initialize

[Badhi]

I want to override the behavior for Initialize feature on the server and was able to do it overriding the lsp_initialize of LanguageProtocol like below

class CustomeProtocol(LanguageProtocol):
     def lsp_initialize(config):
         result = super().lsp_initialize(config)
         status = my_server_initialize(config)
         return result

In the protocol I could see that we could use InitializeError to update client on server initialization failure. But I can't find a way to return this error along with the results. Is there a way to do it?

[tombh]

Currently Pygls' return signature for LanguageProtocol.lsp_initialize is just InitializeResult. But I think it should actually be Union[InitializeResult, InitializeError]. So strictly speaking, according to the spec, you can't return both an InitializeResult and an InitializeError at the same time to the client. And also the InitializeError interface only has one boolean field for whether the client should retry or not: https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#initializeError So I don't think you can return any more details with the error.

Either way I think you could return the InitializeError like this:

from lsprotocol import types

class CustomeProtocol(LanguageProtocol):
     def lsp_initialize(config):
         ...
         return types.InitializeError(retry=False)

Or maybe you could let the server start anyway, store the error, and report it with server.report_server_error() once the server is up and running?