Why does ale sometimes omit id/seq from LSP/tsserver messages?

[benjaminjkraft]

My question is about this bit of code (and the same bit a few lines above for tsserver):

ale/autoload/ale/lsp.vim

Lines 140 to 142 in af42e0b

	if !l:is_notification
	let l:obj.id = ale#lsp#GetNextMessageID()
	endif

Why the if? It seems like both LSP and tsserver consider id/seq required for all messages. (The blame goes back to the original commits to add LSP, so it isn't very enlightening.)

As far as I know this doesn't break anything in ordinary usage. I'm running into it for the following (admittedly strange) reason: I'm trying to do some performance profiling/logging on tsserver, running a proxy process that logs how long various commands take. But for commands without a seq, it's hard to know what's a response to what. (Obviously some messages from the server aren't a response to anything -- that's fine -- but e.g. geterr does have some kind of response message that it's hard to track.) So I wonder: would it break anything to just always set seq/id?

[w0rp]

The original version of the LSP spec ALE implemented did not require id to be set for a NotificationMessage. There's probably some way we could check which version of the protocol the server is using and set id on notifications. For tsserver, there might be something similar we could do for seq.