Formatting actions should have higher execution priority than "Index: Preparing current file" and such

[MahdiBM]

Swift version

swift-DEVELOPMENT-SNAPSHOT-2025-04-12-a

Platform

macOS 15

Editor

Cursor + the official Swift extension

Description

on-type formatting should not get stuck behind events such as Index: Preparing current file. In fact i don't think any other type of formatting should get stuck behind any other events either.

Steps to Reproduce

Open a file somehow that it triggers Index: Preparing current file using the VSCode extension. Try to trigger on-type formatting. Observe the lag.

Logging

No response

EDIT: The issue seems to be broader than just on-type-formatting. See the next 3 comments.

[kuglee]

Yeah. This is pretty annoying.

[MahdiBM]

@kuglee I wonder if you're experiencing the exact same issue with "on-type-formatting", or some other kind of formatting?
I ask because on-type-formatting is an experimental feature that you need to explicitly enable, and it's more likely that you haven't actually enabled it.

[kuglee]

You're right. I'm experiencing normal formatting action to wait for indexing after changing some code.

[MahdiBM]

I think the problem might be broader than i have reported in this issue ... I do also remember experiencing the same problem even without on-type-formatting.

Let's change the title of the issue.

[MahdiBM]

@ahoppen opinions? I'd guess it won't be trivial to do this unless you've already done something so you can have different "queues" for different kinds of tasks? I vaguely remember some commits about something like that in sourcekit-lsp, but could be totally wrong.

Though even if there is no such mechanism for "multiple queues", it shouldn't be way too hard to implement I'd assume. It'll still require the time though. Just saying the fix looks within reach from my POV, in any case.

[ahoppen]

Formatting etc. does not get stuck behind background indexing. What generally happens is that we have some kind of request running that is based on the document in an old state, we thus can’t handle an edit yet and thus can’t handle the document formatting request because the previous edit hasn’t been processed yet. The best way of telling what’s going on here is to run

log stream --predicate 'subsystem CONTAINS "org.swift.sourcekit-lsp"'  --level debug > /tmp/log.txt

reproduce the issue and then generate a trace file using sourcekit-lsp debug trace-from-signposts and open that with Perfetto. If you could gather that information and share it, that would be highly appreciated.