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Revert "[turbopack] Enable CJS tree shaking by default (#96779)" - #97018

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revert-95993-sp/turbopack/follow-reexportsfrom
revert-96779-sp/turbopack/cjs-tree-shaking-default-on
Aug 10, 2026
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Revert "[turbopack] Enable CJS tree shaking by default (#96779)"#97018
unstubbable merged 1 commit into
revert-95993-sp/turbopack/follow-reexportsfrom
revert-96779-sp/turbopack/cjs-tree-shaking-default-on

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@unstubbable unstubbable commented Aug 10, 2026

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Reverts #96779

With this flag enabled, CJS modules written as var X = module.exports = { … } lose properties that are only read back through the alias.

@mixmark-io/domino (Turndown's server DOM), lib/LinkedList.js:

// source
var LinkedList = module.exports = {
    valid: function(a) { /* … */ return true; },
    insertBefore: function(a, b) {
        utils.assert(LinkedList.valid(a) && LinkedList.valid(b));
// emitted with turbopackCjsTreeShaking: true
var LinkedList = module.exports = {
    ...void function(a) { /* … */ return true; },   // `valid:` key dropped

valid is only referenced via the alias, so it is judged unused and elided, and the elision emits ...void <fnExpr>, i.e. ...undefined, which spreads nothing. Result: TypeError: LinkedList.valid is not a function.

Not domino-specific (same corruption in its NodeUtils.js), and the failure mode is a silent property elision rather than a build error.

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✅ No significant changes detected

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Commit: cdf5539

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Tests Passed

Commit: cdf5539

@unstubbable
unstubbable marked this pull request as ready for review August 10, 2026 10:18
@unstubbable
unstubbable changed the base branch from revert-95993-sp/turbopack/follow-reexports to canary August 10, 2026 10:28
@unstubbable
unstubbable force-pushed the revert-96779-sp/turbopack/cjs-tree-shaking-default-on branch from abc48c2 to cdf5539 Compare August 10, 2026 10:42
@unstubbable
unstubbable changed the base branch from canary to revert-95993-sp/turbopack/follow-reexports August 10, 2026 10:44
@unstubbable
unstubbable merged commit 259abbb into canary Aug 10, 2026
232 of 234 checks passed
@unstubbable
unstubbable deleted the revert-96779-sp/turbopack/cjs-tree-shaking-default-on branch August 10, 2026 11:29
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