We use tsup with turbo in our monorepo to build ~30 packages. I'm on node 20.18.2, but this issue seems present in node 18 as well.

I recently upgraded from tsup 6.7.0 to 8.3.6 and noticed our local build/watch step (tsup --watch) started consuming significantly more CPU (70-100% per process rather than 1-2%), seemingly due to the file watcher. I downgraded back to 6.7.0 and slowly upgraded through each major version, then minor/patch versions, to find out where the issues started.

8.3.0 is the last version where tsup is ~the same CPU usage. Once I bump past 8.3.0, CPU per process spikes and stays high until killed.

Some notes:

• I first tried using pnpm.overrides to downgrade esbuild and rollup to specific prior versions, but didn't see any effect.
• 8.1.1 just doesn't work and all builds exit with Cannot find module '@swc/core' (fixed in 8.1.2)
• 8.3.1 and 8.3.3 don't appear to be installable from npm, despite it being in releases (No matching version found for tsup@8.3.3)

Happy to provide more info and continue debugging if helpful!