Turbopack: Add file write invalidation tracking to filesystem watcher fuzzing #88665

bgw · 2026-01-16T21:39:00Z

In addition to creating task invalidators for file reads, we also create invalidators for file writes. This extends the fuzzer to cover that.

This is a bit trickier to test. Because the write call doesn't return anything, the caller of write never gets invalidated and re-executed, even though write does. So instead, we must observe that write was re-executed by looking at the contents of the file it wrote to. We write a sentinel value to files when we call the turbo-tasks-fs write function, and write random values to it to trigger an invalidation.

I tested this on Windows and Linux.

I don't care about the code quality here, so this was LLM-generated with very lightweight review.

bgw · 2026-01-16T21:39:18Z

Turbopack: Tweak retry loop for link creation to try to fix os error 80 on Windows #88669
Turbopack: Various cleanup for turbo-tasks-fs, mostly retry logic and string formatting #88668
Turbopack: Add a stress test / fuzzer that tries creating many symlinks in a tight loop #88667
Turbopack: Move fuzzer for fs watcher into a separate file/module #88666
Turbopack: Add file write invalidation tracking to filesystem watcher fuzzing #88665 👈 (View in Graphite)
Turbopack: Extend filesystem watcher fuzzing to cover symlinks and junction points #88192
canary

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codspeed-hq · 2026-01-16T22:02:21Z

Merging this PR will not alter performance

✅ 17 untouched benchmarks
⏩ 3 skipped benchmarks¹

_{Comparing bgw/fuzz-track-writes (a21d325) with canary (d2ea7d3)}

3 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

lukesandberg · 2026-01-20T16:50:16Z

that codspeed result really says it all doesn't it. just pure noise

bgw · 2026-01-20T20:33:36Z

Merge activity

Jan 20, 8:33 PM UTC: A user started a stack merge that includes this pull request via Graphite.
Jan 20, 8:35 PM UTC: Graphite rebased this pull request as part of a merge.
Jan 21, 6:08 PM UTC: @bgw merged this pull request with Graphite.

nextjs-bot · 2026-01-20T20:50:26Z

Tests Passed

nextjs-bot · 2026-01-20T20:56:47Z

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Warm = With cached build artifacts

Build Metrics:

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Change Thresholds:

Time: Changes < 50ms AND < 10%, OR < 2% are insignificant
Size: Changes < 1KB AND < 1% are insignificant
All other changes are flagged to catch regressions

⚡ Dev Server

Metric	Canary	PR	Change	Trend
Cold (Listen)	456ms	456ms	✓	▁▁▁▁█
Cold (Ready in log)	446ms	446ms	✓	▅▂█▆▄
Cold (First Request)	857ms	850ms	✓	▇▁█▇▃
Warm (Listen)	456ms	455ms	✓	▁▁▁▁█
Warm (Ready in log)	447ms	447ms	✓	▁▃▁▁█
Warm (First Request)	357ms	356ms	✓	▅█▇▁▇

📦 Dev Server (Webpack) (Legacy)

📦 Dev Server (Webpack)

Metric	Canary	PR	Change	Trend
Cold (Listen)	456ms	455ms	✓	▁▁▁▁▁
Cold (Ready in log)	440ms	440ms	✓	▅▇▅▄▅
Cold (First Request)	1.801s	1.820s	✓	▅█▅▃▄
Warm (Listen)	456ms	456ms	✓	▁█▁▁▁
Warm (Ready in log)	440ms	438ms	✓	▆█▆▆▅
Warm (First Request)	1.819s	1.820s	✓	▄█▄▃▃

⚡ Production Builds

Metric	Canary	PR	Change	Trend
Fresh Build	4.659s	4.663s	✓	▁▄▁▁█
Cached Build	4.657s	4.660s	✓	▂▆▁▁█

📦 Production Builds (Webpack) (Legacy)

📦 Production Builds (Webpack)

Metric	Canary	PR	Change	Trend
Fresh Build	13.974s	13.997s	✓	▁▅▂▁▁
Cached Build	14.029s	14.065s	✓	▂▇▂▁▁
node_modules Size	459 MB	459 MB	✓	▅████

📦 Bundle Sizes

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Main Bundles: **431 kB** → **431 kB** ✅ -39 B

82 files with content-based hashes (individual files not comparable between builds)

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Middleware

	Canary	PR	Change
middleware-b..fest.js gzip	763 B	762 B	✓
Total	763 B	762 B	✅ -1 B

Build Details

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_buildManifest.js gzip	450 B	450 B	✓
Total	450 B	450 B	✓

📦 Webpack

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2086.HASH.js gzip	169 B	N/A	-
2161-HASH.js gzip	5.41 kB	N/A	-
2747-HASH.js gzip	4.48 kB	N/A	-
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main-HASH.js gzip	38.7 kB	39.1 kB	✓
webpack-HASH.js gzip	1.68 kB	1.68 kB	✓
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_error-HASH.js gzip	182 B	182 B	✓
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middleware-b..fest.js gzip	618 B	617 B	✓
middleware-r..fest.js gzip	155 B	156 B	✓
middleware.js gzip	33 kB	33.3 kB	✓
edge-runtime..pack.js gzip	842 B	842 B	✓
Total	34.7 kB	34.9 kB	⚠️ +237 B

Build Details

Build Manifests

	Canary	PR	Change
_buildManifest.js gzip	738 B	738 B	✓
Total	738 B	738 B	✓

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0.pack gzip	3.67 MB	3.68 MB	🔴 +7.24 kB (+0%)
index.pack gzip	100 kB	99.5 kB	✓
index.pack.old gzip	101 kB	99.6 kB	✓
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🔄 Shared (bundler-independent)

Runtimes

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app-page-exp...dev.js gzip	305 kB	305 kB	✓
app-page-exp..prod.js gzip	162 kB	162 kB	✓
app-page-tur...dev.js gzip	305 kB	305 kB	✓
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app-page-tur...dev.js gzip	301 kB	301 kB	✓
app-page-tur..prod.js gzip	160 kB	160 kB	✓
app-page.run...dev.js gzip	302 kB	302 kB	✓
app-page.run..prod.js gzip	160 kB	160 kB	✓
app-route-ex...dev.js gzip	68.8 kB	68.8 kB	✓
app-route-ex..prod.js gzip	47.6 kB	47.6 kB	✓
app-route-tu...dev.js gzip	68.8 kB	68.8 kB	✓
app-route-tu..prod.js gzip	47.6 kB	47.6 kB	✓
app-route-tu...dev.js gzip	68.4 kB	68.4 kB	✓
app-route-tu..prod.js gzip	47.4 kB	47.4 kB	✓
app-route.ru...dev.js gzip	68.4 kB	68.4 kB	✓
app-route.ru..prod.js gzip	47.4 kB	47.4 kB	✓
dist_client_...dev.js gzip	324 B	324 B	✓
dist_client_...dev.js gzip	326 B	326 B	✓
dist_client_...dev.js gzip	318 B	318 B	✓
dist_client_...dev.js gzip	317 B	317 B	✓
pages-api-tu...dev.js gzip	41.2 kB	41.2 kB	✓
pages-api-tu..prod.js gzip	31.3 kB	31.3 kB	✓
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pages.runtim..prod.js gzip	38.2 kB	38.2 kB	✓
server.runti..prod.js gzip	62.2 kB	62.2 kB	✓
Total	2.71 MB	2.71 MB	✓

nextjs-bot added created-by: Turbopack team PRs by the Turbopack team. Turbopack Related to Turbopack with Next.js. labels Jan 16, 2026

bgw changed the title ~~Turbopack: Add file write invalidation tracking to filesystem fuzzer~~ Turbopack: Add file write invalidation tracking to filesystem watcher fuzzing Jan 16, 2026

bgw requested a review from a team January 16, 2026 21:55

bgw marked this pull request as ready for review January 16, 2026 22:41

lukesandberg approved these changes Jan 20, 2026

View reviewed changes

bgw changed the base branch from bgw/fuzz-symlink-and-junction-watching to graphite-base/88665 January 20, 2026 20:33

bgw changed the base branch from graphite-base/88665 to canary January 20, 2026 20:34

bgw added 5 commits January 20, 2026 20:34

Turbopack: Add file write invalidation tracking to filesystem fuzzer

43942e1

apply effects

beb87a2

use a sentinel value for verifying file writes happened

f2945fa

Junctions on windows point to absolute paths

591f037

Use std::fs::canonicalize before comparing junction paths

a21d325

bgw force-pushed the bgw/fuzz-track-writes branch from 8b47431 to a21d325 Compare January 20, 2026 20:34

bgw merged commit 2912f10 into canary Jan 21, 2026
285 of 288 checks passed

bgw deleted the bgw/fuzz-track-writes branch January 21, 2026 18:08

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Turbopack: Add file write invalidation tracking to filesystem watcher fuzzing #88665

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