fix: remove unnecessary __webpack_require__ in ESM library output#21032
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🦋 Changeset detectedLatest commit: bd64378 The changes in this PR will be included in the next version bump. This PR includes changesets to release 1 package
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## main #21032 +/- ##
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- Coverage 91.58% 91.57% -0.02%
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Files 573 573
Lines 59541 59555 +14
Branches 16077 16084 +7
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+ Hits 54532 54536 +4
- Misses 5009 5019 +10
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When a chunk contains non-JS modules (CSS, assets) alongside a concatenated ESM entry, the runtime cleanup hook in ModuleLibraryPlugin bailed out because getNumberOfChunkModules > 1, leaving unused __webpack_require__.d and __webpack_require__.o helpers in the output. - HarmonyExportInitFragment: only add definePropertyGetters requirement when exportMap is non-empty - ModuleLibraryPlugin: replace coarse getNumberOfChunkModules check with per-module requirement inspection Closes #21029
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Summary
When an ESM library chunk (
output.library.type = "module") contains non-JS modules (CSS viaexperiments.css,MiniCssExtractPlugin, asset modules, etc.) alongside a concatenated entry,__webpack_require__runtime helpers (var __webpack_require__ = {},__webpack_require__.d,__webpack_require__.o) are emitted even though they are never referenced in the output.Root cause:
ModuleLibraryPlugin's cleanup hook bailed out whengetNumberOfChunkModules(chunk) !== 1, but CSS/asset modules increase the count without actually needing those JS helpers.Two fixes:
HarmonyExportInitFragment.getContent()— only adddefinePropertyGettersandexportsruntime requirements whenexportMapis non-empty. Previously these were added unconditionally even when the fragment produced no output.ModuleLibraryPlugincleanup hook — replace the coarsegetNumberOfChunkModules !== 1guard with a per-module check: iterate chunk modules and only retain helpers that another module actually requires.Fixes #21029
What kind of change does this PR introduce?
fix
Did you add tests for your changes?
Yes. Added
entry4.js+style.cssto the existingtest/configCases/library/module-useless-export-requirement/test case, covering the ESM library + CSS module combination. Updated 4 HTML snapshot files that previously contained the unnecessary helpers.Does this PR introduce a breaking change?
No. This only removes dead runtime code from the output.
If relevant, what needs to be documented once your changes are merged or what have you already documented?
n/a
Use of AI
Claude Code was used to investigate the root cause, draft the implementation, and write the test case, under human review.