Overview

Following up onhttps://twitter.com/OliverJAsh/status/1757013260698607983:

@JoshuaKGoldberg@bradzacher 👋 After upgrading typescript-eslint from 6.15 to 6.16 we're having perf issues. It seems to be related to EXPERIMENTAL_useProjectService +#7752. I'd like to file an issue but I'm struggling to create a reduced test case for it.

@OliverJAsh and I went over the reproduction in a 1:1 just now (thanks again Oliver! 🙌). It was in fact#7752's changes touseProgramFromProjectService. Specifically the changes to the file path provided toprojectService.openClientFile. Roughly:

-  const opened = projectService.openClientFile(-    absolutify(parseSettings.filePath),+  const filePath = getCanonicalFileName(parseSettings.filePath);+  const opened = service.openClientFile(+    ensureAbsolutePath(filePath, service.host.getCurrentDirectory()),

The resultant file path provided changed casing. Roughly:

- /Users/user/repos/path/to/file.ts+ /users/user/repos/path/to/file.ts

This, for some reason, caused the project service to jump from ~5-7 seconds of file parse time to ~30-50 seconds or so.

cc@jakebailey as FYI.