Make DocumentSyncListener more efficient if no server is running

[jwortmann]

Currently if LSP (this package) is installed, it runs quite some code in the background whenever the callbacks from DocumentSyncListener, which is a subclass of sublime.ViewEventListener, are triggered. This happens for all views, not only when a server is active. For example it creates an empty (if no server is running) sublime.CompletionList and schedules to run more code on the async thread in

LSP/plugin/documents.py

Lines 555 to 560 in a6b17a4

	def on_query_completions(self, prefix: str, locations: list[int]) -> sublime.CompletionList | None:
	completion_list = sublime.CompletionList()
	triggered_manually = self._auto_complete_triggered_manually
	self._auto_complete_triggered_manually = False # reset state for next completion popup
	sublime.set_timeout_async(
	lambda: self._on_query_completions_async(completion_list, locations[0], triggered_manually))

or it runs the debouncing in

LSP/plugin/documents.py

Line 384 in a6b17a4

def on_selection_modified_async(self) -> None:

via sublime.set_timeout_async each time when the cursor position changes.

All of this runs on the async thread, so you won't immediately experience any lag from this. But still it feels very inefficient and I wondered how it could be prevented or improved. We can't use the is_applicable classmethod for DocumentSyncListener, because if the view's syntax is changed later, an LSP session might still get attached to this view. So my idea would be to add a check in each of the ST callback methods and return early if there is no session running for this view. Does it make sense or is there a better solution?

[rchl]

One thing that is a potential concern is that there could be a case where we rely on given method cleaning up stuff after session is destroyed. For example on restarting session. Though I know that there already exist issues with that so if we'll notice something not working correctly with this change included, it might not be due to it actually...

[rchl]

Some crazy type stuff that I'm not gonna invest time in learning now but I'm glad you found a way to type this properly :)