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fix: invalidate provided-exports cache with lazy barrel#21326

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alexander-akait merged 1 commit into
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fix-lazy-barrel-flag-dep
Jul 3, 2026
Merged

fix: invalidate provided-exports cache with lazy barrel#21326
alexander-akait merged 1 commit into
mainfrom
fix-lazy-barrel-flag-dep

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@hai-x

@hai-x hai-x commented Jul 1, 2026

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Summary

What kind of change does this PR introduce?

Fixes #21318.

A lazy barrel cached while its re-export targets were deferred could serve stale provided exports after a later build un-defers a target, producing link error "export 'x' was not found". Two independent cache layers had this staleness; each gets its own fix.

  1. persistent provided-exports cache (FlagDependencyExportsPlugin)
  • lib/FlagDependencyExportsPlugin.js: the cache etag was buildInfo.hash alone; it's now a plain string etag that appends the barrel's sorted still-lazy request keys: ${hash}|${[...lazyKeys].sort().join("|")}. No hashing (etags are only string-compared downstream), no buildInfo state.
  • lib/LazyBarrel.js: the still-lazy keys are derived from state the controller already maintains: new LazyBarrelInfo.getLazyRequestKeys() (the _requestToDepGroup map keys) and LazyBarrelController.getLazyRequestKeys(module). Nothing is mirrored, mutated in sync, or serialized into the persistent cache.
  1. unaffected-module mem cache (experiments.cacheUnaffected)
  • lib/Compilation.js: compareReferences assumed a non-rebuilt module's connection set is stable, an invariant lazy-barrel deferral breaks: un-deferring adds a connection without rebuilding the barrel. If the target module already existed unchanged, no other invalidation caught it and the stale memCache short-circuited in front of Fix 1. The snapshot is now { map, count }, both sides apply the same dep filter so a map miss unambiguously means an added connection (immediate invalidation), and the count catches removals. The Add+remove pairs can't mask each other since additions are detected per-entry.

Tests

  • test/PersistentCaching.test.js: cross-process stale-barrel case for Fix 1 (plus an mkdir fix for nested fixture paths).
  • test/watchCases/lazy-barrel/stale-star-exports: new watch case: deferred star target imported on rebuild, plus a named re-export (sub2) variant.
  • test/watchCases/lazy-barrel/stale-star-exports-mem-cache: new watch case reproducing Fix 2's scenario: the star target pre-exists via a direct import (so it's "unchanged"), then gets imported through the barrel under cache.cacheUnaffected. Failed before Fix 2, passes now.
  • test/watchCases/lazy-barrel/unsafe-cache/, build-on-new-import: enable exportsPresence: "error" so stale provided exports fail loudly; unsafe-cache step 0 now starts from a fully-deferred state (the "requesting a builds its target" invariant moved to step 1's expect(a).toBe("a")).

Did you add tests for your changes?

Yes

Does this PR introduce a breaking change?

No

If relevant, what needs to be documented once your changes are merged or what have you already documented?

n/a

Use of AI

Partial

@changeset-bot

changeset-bot Bot commented Jul 1, 2026

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🦋 Changeset detected

Latest commit: 0f6670e

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

This PR includes changesets to release 1 package
Name Type
webpack Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

@github-actions

github-actions Bot commented Jul 1, 2026

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This PR is packaged and the instant preview is available (7639066).

Install it locally:

  • npm
npm i -D webpack@https://pkg.pr.new/webpack@7639066
  • yarn
yarn add -D webpack@https://pkg.pr.new/webpack@7639066
  • pnpm
pnpm add -D webpack@https://pkg.pr.new/webpack@7639066

@codecov

codecov Bot commented Jul 1, 2026

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.47%. Comparing base (3cb8578) to head (0f6670e).
⚠️ Report is 9 commits behind head on main.

Additional details and impacted files
@@            Coverage Diff             @@
##             main   #21326      +/-   ##
==========================================
- Coverage   92.86%   92.47%   -0.40%     
==========================================
  Files         594      594              
  Lines       65210    65335     +125     
  Branches    18143    18189      +46     
==========================================
- Hits        60559    60417     -142     
- Misses       4651     4918     +267     
Flag Coverage Δ
css-parsing 28.65% <53.12%> (+0.04%) ⬆️
html5lib 28.23% <53.12%> (-2.91%) ⬇️
integration 88.84% <100.00%> (-0.04%) ⬇️
test262 45.52% <53.12%> (-0.04%) ⬇️
unit 43.23% <53.12%> (+0.15%) ⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

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@codspeed-hq

codspeed-hq Bot commented Jul 1, 2026

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Merging this PR will improve performance by 40.13%

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 2 improved benchmarks
❌ 2 regressed benchmarks
✅ 140 untouched benchmarks

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

Mode Benchmark BASE HEAD Efficiency
Memory benchmark "many-modules-esm", scenario '{"name":"mode-development","mode":"development"}' 1.1 MB 1.9 MB -39.59%
Memory benchmark "wasm-modules-async", scenario '{"name":"mode-development-rebuild","mode":"development","watch":true}' 189.6 KB 246.9 KB -23.23%
Memory benchmark "asset-modules-inline", scenario '{"name":"mode-development-rebuild","mode":"development","watch":true}' 1,194.8 KB 382.6 KB ×3.1
Memory benchmark "wasm-modules-sync", scenario '{"name":"mode-development-rebuild","mode":"development","watch":true}' 354 KB 132.9 KB ×2.7

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.


Comparing fix-lazy-barrel-flag-dep (0f6670e) with main (c2628cf)

Open in CodSpeed

@alexander-akait

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@hai-x looks good let’s merge and make the patch release

@hai-x hai-x force-pushed the fix-lazy-barrel-flag-dep branch from c1240b0 to e1774fa Compare July 2, 2026 16:18
@hai-x

hai-x commented Jul 2, 2026

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@alexander-akait

Thanks for the review! I've reworked the approach in two ways:

  • No more buildInfo state. The still-lazy re-export request keys are now derived from LazyBarrelController's per-compilation state (getLazyRequestKeys), so no need to store it on the module.
  • Fixed a related staleness under experiments.cacheUnaffected. The module mem cache restores provided exports before the disk cache check. The reference snapshot now records a connection count, so added/removed connections invalidate the mem cache.

Could you take another look?

@hai-x hai-x marked this pull request as ready for review July 2, 2026 16:28
@Knagis

Knagis commented Jul 2, 2026

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tried with the current patch and seems this doesn't fix the issue.

i delete webpack cache and start a fresh build, few lazy compilations later it throws

Webpack cache efficiency: 0% (0/113)
Webpack cache efficiency: 3% (112/3948)
Webpack cache efficiency: 97% (3948/4062)
export 'useLocalObservable' (imported as 'useLocalObservable') was not found in 'mobx-react' (possible exports: MobXProviderContext, PropTypes, Provider, disposeOnUnmount, inject, observer)
export 'useLocalObservable' (imported as 'useLocalObservable') was not found in 'mobx-react' (possible exports: MobXProviderContext, PropTypes, Provider, disposeOnUnmount, inject, observer)
export 'useLocalObservable' (imported as 'useLocalObservable') was not found in 'mobx-react' (possible exports: MobXProviderContext, PropTypes, Provider, disposeOnUnmount, inject, observer)

@Knagis

Knagis commented Jul 2, 2026

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now that i can reproduce the issue consistently locally, this PR behaves the same as 5.108.3, while #21322 prevents the errors.

@Knagis

Knagis commented Jul 2, 2026

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though i applied only this PR on top of 5.108.3, in case this depends on something else merged after 5.108.3...

@hai-x

hai-x commented Jul 2, 2026

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though i applied only this PR on top of 5.108.3, in case this depends on something else merged after 5.108.3...

@Knagis Hi, have you try the version, or just edit the webpack code in the node_modules?

@alexander-akait

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@Knagis can you try to remove the old cache and run code with this patch

@alexander-akait

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The PR which I closed just disable cache, yes it is the fix, but the solution is not good, ideally we should find the root of the problem and keep cache

@hai-x

hai-x commented Jul 2, 2026

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@Knagis Could you share some reproduction steps? I can repro it with filesystem cache by following steps:

  1. Clean the disk cache.
  2. Write index.js and then build it.
import { PropTypes } from "mobx-react";

console.log(PropTypes);
  1. Update index.js and then build it.
import { useLocalObservable } from "mobx-react";

console.log(useLocalObservable);

@Knagis

Knagis commented Jul 2, 2026

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i'm taking https://patch-diff.githubusercontent.com/raw/webpack/webpack/pull/21326.patch and adding it as yarn patch on top of 5.108.3 (we have all kinds of rules in place that force npm packages from our own repository etc. so patch is the easiest)

in my scenario it now fails with just memory cache, not even restarting the build (initial build, then one lazy chunk builds and then the next one fails).

@hai-x

hai-x commented Jul 2, 2026

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in my scenario it now fails with just memory cache, not even restarting the build (initial build, then one lazy chunk builds and then the next one fails).

Make sense, let me try it with memory cache and lazy compilation. Thanks for sharing.

@hai-x hai-x force-pushed the fix-lazy-barrel-flag-dep branch 2 times, most recently from eda84cc to 56d1fc0 Compare July 2, 2026 21:22
@hai-x

hai-x commented Jul 2, 2026

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@Knagis Yeah, this issue is about unsafe memory cache with cacheUnaffected. Could you try the latest patch? Thanks.

@hai-x hai-x force-pushed the fix-lazy-barrel-flag-dep branch from 56d1fc0 to c4e91c9 Compare July 3, 2026 07:55
@hai-x hai-x force-pushed the fix-lazy-barrel-flag-dep branch from c4e91c9 to 0f6670e Compare July 3, 2026 09:21
@github-actions

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Types Coverage

Coverage after merging fix-lazy-barrel-flag-dep into main will be
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@alexander-akait

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@Knagis friendly ping, want to make the patch release

@Knagis

Knagis commented Jul 3, 2026

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Right now with the latest version of this PR i can no longer reproduce the error. Not that i could reproduce all the cases before :)

@alexander-akait

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@Knagis lets try, if you faced with the issue agin after the patch release feel free to open a new issue

@alexander-akait alexander-akait merged commit 7639066 into main Jul 3, 2026
104 of 105 checks passed
@alexander-akait alexander-akait deleted the fix-lazy-barrel-flag-dep branch July 3, 2026 20:03
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Lazy compilation + FS cache = incorrect export X (imported as X) was not found in ...

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