[alexander-akait]

Summary

webpack pauses its watcher during a build. When the build ends, it attaches a new watcher with the build's start time and closes the paused one. Anything the paused watcher saw in between is dropped. For files, the new watcher catches up by comparing the file's time with the start time ("outdated on attach"). Directories had no stored time, so a watched missing directory that appeared during the build, e.g. a nested node_modules, was never reported. The rebuild waited for some unrelated change.

This was found through webpack's runtimes (deno) job, which runs the watch tests with polling. WatchCacheUnaffectedTestCases › cache › managedPath failed about 1 run in 20 under load, on watchpack 2.6.1 and 2.6.2 alike. Native watching can hit it too; polling widens the window.

The fix:

• DirectoryWatcher keeps, per directory, the time it was noticed (directorySafeTimes). watch() uses that time when the target is a known directory.
• It uses the time noticed rather than the creation time. A poll can notice a directory created just before the next build started, and that build did not see it either: it read webpack's cached "missing" state.
• Internal watchers attach with start time 1 to wait for a directory to (re)appear. They are excluded. Otherwise a removed directory that the parent still lists fires that watcher at once, and the retry loops forever.

Tests

test/DirectoryOutdatedOnAttach.test.js:

Case	main	This PR
Directory appears while the paused watcher listens (native)	fails	passes
Same, with polling	fails	passes
Created just before the start time, noticed after it	fails	passes
Removed directory still listed by its parent: no retry loop	passes	passes (fails without the start-time-1 guard)

The full suite passes natively (213) and with WATCHPACK_POLLING=200, file by file. npm run lint is clean.

Checked in webpack under Deno, 40 runs under load: the missed change and the hangs are gone. The remaining failure there is a separate webpack issue: experiments.cacheUnaffected does not re-resolve a module when only a missing directory appears. I'll take that up in webpack.

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Generated by Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Watchers now detect directories that appear while a previous watcher is paused, including when polling is enabled, rather than waiting for an unrelated change.
  • Removed directories no longer cause repeated retries when still listed by their parent.

[changeset-bot]

🦋 Changeset detected

Latest commit: b0ec512

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
watchpack	Patch

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[codspeed]

Merging this PR will not alter performance

⚠️ 1 benchmark spent significant time in system calls

System calls cannot be consistently instrumented, so they are not included in the measure, which understates the real cost. Please switch to the Walltime instrument to accurately measure system calls.

Measurement and system calls

• ignored-cross-platform: regex against windows paths

✅ 36 untouched benchmarks

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_{Comparing fix/directory-outdated-on-attach (b0ec512) with main (8cc6635)}

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

• Configuration used: Organization UI
• Review profile: CHILL
• Plan: Advanced
• Run ID: ada47a60-ed08-4537-89c9-48991aa46d3d

📥 Commits

Reviewing files that changed from the base of the PR and between 8cc6635 and b0ec512.

📒 Files selected for processing: 4

• .changeset/directory-outdated-on-attach.md
• lib/DirectoryWatcher.js
• test/DirectoryOutdatedOnAttach.test.js
• types/DirectoryWatcher.d.ts

Included review availability: This review used your included allowance. Your plan provides up to 2 included reviews per hour; 1 remain after this review.

Walkthrough

DirectoryWatcher now records the safe time for each noticed directory and removes that record when the directory is marked missing. When a target has no file entry, a watcher with a start time greater than 1 can use the recorded directory time. Added tests cover directory reporting across paused and newly attached watchers, polling, and retries after directory removal.

Priority: ⬇️ Low

Severity of issue fixed: Low

Merge Risk: ⚪ Minimal · up to b0ec5

No actionable issue remains from the reviewed changes. Merge after normal checks.

Pre-merge checks: 5

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly describes the main change: reporting a directory that appeared while no watcher was listening when the next watcher attaches.
Docstring Coverage		No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 3…
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

Full details: Docstring Coverage

Explanation

No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 3 files. (1 skipped: 1 unsupported.)

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.76%. Comparing base (8cc6635) to head (b0ec512).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #361      +/-   ##
==========================================
- Coverage   92.87%   92.76%   -0.12%     
==========================================
  Files           8        8              
  Lines        1404     1409       +5     
  Branches      421      423       +2     
==========================================
+ Hits         1304     1307       +3     
- Misses         94       96       +2     
  Partials        6        6              

Flag	Coverage Δ
integration	92.76% <100.00%> (-0.12%)	⬇️

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[alexander-akait]

codecov/project is red at −0.12% (2 lines), but this PR doesn't cause it. All lines it changes are covered (codecov/patch passes).

A local coverage run of lib/, main vs this branch, leaves the same 197 statements uncovered on both. Every difference is the same statement shifted by the lines this PR adds. So the 2 lines come from timing-dependent code that some of the 42 CI jobs reach on one run and miss on another. No fix ported, since there is nothing in this PR to fix.

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Generated by Claude Code