fix(app-tools): stop writing the ESM loader files twice - #8819
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`src/esm` is matched by the `./src/**` entry, so the bundler emits those
files itself. It also sits in `output.copy`, and in the ESM outputs both land
on the same `.mjs` paths — two writers for one file. When the writes
interleave the file is left truncated, and since `bin/modern.js` loads
`dist/esm-node` for any project with `"type": "module"`, a corrupt loader
takes the whole project down at startup:
SyntaxError: Unexpected token '}'
at compileSourceTextModule (node:internal/modules/esm/utils)
Windows CI hit exactly that, with dist/esm-node/esm/register-esm.mjs and
ts-node-loader.mjs unparsable while the CommonJS fixtures were unaffected —
the CJS output emits `.js`, so nothing collides there.
Keep the copy only for the CJS output, which is where it is the sole source
of the `.mjs` loaders `register()` resolves by name. Rebuilding with this
change produces a byte-identical dist, so the duplicate write was the only
thing removed.
The deploy templates are already excluded from the entry for the same reason.
Co-Authored-By: Riff
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zllkjc
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Aug 25, 2026
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Summary
src/esmis matched by the./src/**entry, so the bundler emits those files itself. It also sits inoutput.copy, and in the ESM outputs both land on the same.mjspaths — two writers for one file. When the writes interleave the file is left truncated.bin/modern.jsloadsdist/esm-nodefor any project with"type": "module", so a corrupt loader takes the whole project down at startup:Evidence
Windows CI had been red since Aug 13. Every failing fixture was
"type": "module"; every passing one was CommonJS — including tailwind v2/v3 passing in the same suite where v4 failed. Parsing the published ESM build during a failing run named the files:The CJS output emits
.js, so nothing collides there — which is why CommonJS projects were never affected.Fix
Keep the copy only for the CJS output, where it is the sole source of the
.mjsloadersregister()resolves by name. Removing it entirely breaks CJS; excludingsrc/esmfrom the entry breaks CJS too, becausedist/cjs/utils/register.jsimports../esm/register-esm.js, which only exists as a bundled entry.Rebuilding with this change produces a byte-identical dist (
diff -rqbefore/after: 0 differences), so the duplicate write was the only thing removed.The deploy templates are already excluded from the entry for exactly this reason;
src/esmwas missed.Verification
Windows integration tests on this fix (plus #8816 for an unrelated test-side failure): 87 passed | 4 skipped, 0 failed —
SyntaxError,compileSourceTextModuleandERR_CONNECTION_REFUSEDall gone.Note this is not test-only: these files ship inside the npm package, and a release build runs the same racy config.
@modern-js/app-tools@3.8.2on the registry is currently clean (all 100esm-node.mjsparse), but a release that loses the race would publish a broken loader and break every"type": "module"user project at startup.Co-Authored-By: Riff