feat: keep export mangling for modules whose namespace object escapes#21234
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LGTM, it's nice improvement for the whole namespace accessing. |
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When a module's namespace object is used as a whole value (for example re-exported and returned, spread, or passed around) export mangling was disabled for the whole module, bloating every reference in all other consumers. Such modules now keep their exports mangleable: the escaping reference is rendered as a decoupled namespace object that exposes the original export names via getters onto the mangled bindings, so access by the original name keeps working. Driven by optimization.mangleExports, for both non-concatenated and concatenated builds. Left conservative (unchanged) for CommonJS interop, dynamic imports and deferred imports. To preserve ES module namespace semantics on the escaping module, its exports stay non-inlinable and member access keeps a qualified property access: a missing export reads as `ns.x` (not a bare `undefined`) and `delete ns.x` hits a real non-configurable binding, so it stays valid and throws where the spec requires. Closes #19153.
Clarify the PR-body guidance to use the auto-closing `Closes #…`/`Fixes #…` form when the PR actually fixes the bug or implements the requested feature, reserving `Refs #…` for issues a PR only relates to.
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Summary
When a module's namespace object is used as a whole value (for example re-exported and returned, spread, or passed around), export mangling was disabled for the entire module, so every reference in all other consumers kept full export names — bloating the output.
This PR keeps such modules mangleable: the escaping reference is rendered as a decoupled namespace object whose getters expose the original export names onto the mangled bindings, so access by the original name (including dynamic/
Object.keys) keeps working. It is driven byoptimization.mangleExportsand works for both non-concatenated and concatenated builds (inner, external/standalone, and code-split shared modules). CommonJS interop, dynamic imports and deferred imports are left conservative (unchanged). Closes #19153.On a barrel-with-escape build (1 escaping module, 300 exports, 150 static consumers, minified) the output drops from 38.4 KB → 17.2 KB raw (−55%) / 5.3 KB → 4.3 KB gzip (−19%), with no build-time or peak-memory regression.
What kind of change does this PR introduce?
feat
Did you add tests for your changes?
Yes — new
test/configCases/mangle/mangle-escaping-namespaceand…-concatcases covering ESM named/default exports,export * asre-exports, CommonJS interop, destructuring of an escaping module, dynamically imported namespaces, inlined-const exports, namespace enumeration, anddelete ns.memberon an escaping namespace; plus updatedmangle-with-destructuring-assignmentandcode-generation/re-export-namespace-concatto the new (runtime-identical) output. Verified against thetest262module-namespace[[Delete]]cases.Does this PR introduce a breaking change?
No. Runtime semantics are unchanged (verified across all the contexts above); only the generated output is smaller because more exports get mangled.
If relevant, what needs to be documented once your changes are merged or what have you already documented?
n/a — no new option;
optimization.mangleExportsnow also applies to modules whose namespace object escapes.Use of AI
AI (Claude Code) was used to implement the change, write the tests, run the test suite, measure output size / build time / memory, and investigate edge cases across rendering contexts. All output was reviewed and validated against the webpack test suite.
Generated by Claude Code