Degraded pages-directory build performance in next.js@v13.2.5-canary.26 and higher

I've ran into significant build performance issues since upgrading next.js from v13.2.4 to v13.3.0 or higher. The build duration of a project I'm working on became easily 2-7x slower after the upgrade. Building on vercel usually takes about 10 minutes, but after the upgrade it was 25-30 minutes, unacceptable in my workflow so I had to revert to v13.2.4.

After a lot of digging I was able to narrow it down to the v13.2.5-canary.26 release.

Luckily, it is easy to reproduce the issue with this simple next.js repo.

Steps to reproduce

This repo contains a simple next.js project with a pages-directory containing 200 pages (/number/[number].tsx) which fake a 1 second delay before rendering the page. Not sure if this is relevant, but it helps to make the issue more visible.

1. Clone this repo
2. Run npm install - this will install next@v13.2.4
3. Run rm -rf .next to remove the build cache (if any)
4. Run npm run build - measure the build duration
5. Run npm install next@v13.2.5-canary.26
6. Run rm -rf .next to remove the build cache
7. Run npm run build - measure the build duration

The second build will/should be significantly slower. See below for my results in finding the offending release.

Results

• 0m30s for next@v13.2.4
  30 seconds is the expected duration
• 0m31s for next@v13.2.5-canary.14
• 0m30s for next@v13.2.5-canary.22
• 0m31s for next@v13.2.5-canary.24
• 0m31s for next@v13.2.5-canary.25
• 3m30s for next@v13.2.5-canary.26
  ⚠️ this is where the build duration starts to degrade (next@v13.2.5-canary.26 release notes)
• 3m34s for next@v13.2.5-canary.28
• 3m33s for next@v13.2.5-canary.29
• 3m23s for next@v13.3.4
  maybe it got fixed somewhere in the v13.3.x range, but 13.3.4 doesnt show any improvement
• 1m01s for next@v13.4.5
  good improvement in next's latest release(s), but still 2x slower than v13.2.4
• 1m02s for next@13.4.6-canary.0