Incremental rebuild performance regression in v5.54.0

Bug report

What is the current behavior? Webpack spends several seconds inside of lib/Watching.js after an incremental rebuild:

This profile is from 5.54.0:

And I verified it’s still an issue in 5.67.0 (as well as a few versions in between):

If the current behavior is a bug, please provide the steps to reproduce. I’m not sure how to reproduce this outside of our app, I think it’s only really noticeable by it being a large application. I’ve included the profiles from the debugger, so I hope that’s enough to go on? If not let me know if there’s anything else I can do to help diagnose the root cause.

What is the expected behavior? Webpack should spend only about a second on this step. This profile is from 5.53.0 (but also seeing the same lower speeds on 5.50.0 and 5.52.1 so I’m confident it’s not a fluke)

Other relevant information: webpack version: All versions of webpack from 5.54.0 Node.js version: v16.13.1 Operating System: MacOS Monterey Additional tools: This is being run from the angular cli

[gluxon]

https://github.com/webpack/webpack/pull/15991 may address this partially. I don’t know if it’ll bring the 7.65s Watching.js call back down to 1.02s, but it should be much less.

[mattlewis92]

Very strange because we don’t change nothing related to watch in 5.53, maybe something in plugins, can you locally debug?

I’ll do what I can to debug locally and see if I can work out what’s wrong.

@mattlewis92 Do you use exactly same project/setup ? Is it possible reduce issue to reproducible repo ?

Yep exactly the same each time, all I did between each of those profiles was run npm i -D webpack@version and then run an incremental rebuild. I’m not sure how to reproduce it standalone in a repo as our app is enormous, and I suspect the problem is caused by it being a large app, rather than a specific issue within it.