fix: minify .bundle assets with terser-webpack-plugin 5.6.0 and newer

[giaBaoJS]

Summary

Configure Re.Pack's own minify wrapper on TerserPlugin instead of relying on the plugin's built-in terserMinify.

Why

terser-webpack-plugin 5.6.0 added per-minimizer asset filters, and its terser implementation declares terserMinify.filter = (name) => /\.[cm]?js(\?.*)?$/i.test(name) (dist/utils.js:312). Re.Pack emits index.bundle and [name].chunk.bundle, so every asset is rejected by that filter and dropped from assetsForMinify before minification runs. Nothing is reported: no error, no warning, and the asset is not flagged [minimized] in stats. Production bundles simply ship unminified.

This hits webpack and Rspack alike, and pinning terser-webpack-plugin in this repo does not cover it: getTerserPlugin prefers the copy resolved from the project root, so any app that resolves 5.6.0 or newer still gets the silent no-op.

Implementation

The plugin only consults filter on the implementation it is handed. A plain function has no filter property, so wrapping terserMinify makes every version accept .bundle assets:

function repackTerserMinify(input, sourceMap, minimizerOptions, extractComments) {
  return require('terser-webpack-plugin').terserMinify(
    input, sourceMap, minimizerOptions, extractComments
  );
}

repackTerserMinify.getMinimizerVersion = () =>
  require('terser-webpack-plugin').terserMinify.getMinimizerVersion?.();

terserMinify is exported by 5.5.0 as well, so the wrapper behaves identically on old and new versions. The plugin serializes it into a jest worker (getWorker().transform(serialize(options))) and re-evaluates it there with its own require, which is why the wrapper closes over nothing and resolves terser-webpack-plugin by name.

getMinimizerVersion is forwarded because the plugin reads it on the main thread to build the chunk hash (index.js:686 on 5.5.0, index.js:724 on 5.6.1). Without the forward that slot silently degrades to the "0.0.0" literal and a bare terser upgrade stops invalidating persistent cache. It is never read inside the worker, and serialization drops function statics anyway, so attaching it cannot affect the worker path.

Closes #1390.

Validation

• pnpm --filter @callstack/repack test: 35 suites, 315 tests passed
• pnpm --filter @callstack/repack typecheck and biome check: clean
• reverting only getMinimizerConfig.ts while keeping the new tests turns should minify .bundle assets with a plugin that only accepts .js red on expect(implementation.filter).toBeUndefined() with Received: [Function acceptsJsOnly], so it fails because the .bundle asset is filtered out, not on an import or compile error
• end to end in apps/tester-app with terser-webpack-plugin@5.6.1 resolved at the app root, react-native bundle --platform ios --entry-file index.js --dev=false:

bundler	without the wrapper	with the wrapper
webpack 5.105.4	4,846,598 bytes, full identifier names	1,969,176 bytes
Rspack 1.6.0	4,822,812 bytes, full identifier names	1,969,836 bytes

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[changeset-bot]

🦋 Changeset detected

Latest commit: f2caf84

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

This PR includes changesets to release 6 packages

Name	Type
@callstack/repack	Patch
@callstack/repack-plugin-expo-modules	Patch
@callstack/repack-plugin-nativewind	Patch
@callstack/repack-plugin-reanimated	Patch
@callstack/repack-dev-server	Patch
@callstack/repack-init	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

[dannyhw]

I understand the desire to fix this but honestly my personal preference will be to fix the rspack minifier rather than continuing to default to terser

[MikitasK]

I understand the desire to fix this but honestly my personal preference will be to fix the rspack minifier rather than continuing to default to terser

makes sense 👍 since webpack is affected too, wdyt about keeping this fallback for webpack, but using/fixing native minimizer for rspack?

[dannyhw]

but i believe terser still works for webpack, don't we already prefer the users version for that?

[giaBaoJS]

I measured it before answering, and terser does not still work for webpack. Same root cause as Rspack.

terser-webpack-plugin 5.6.0 added terserMinify.filter = (name) => /\.[cm]?js(\?.*)?$/i.test(name) (dist/utils.js:16 and :310). The webpack asset Re.Pack emits is literally index.bundle (plus *.chunk.bundle), so the filter returns false and the plugin drops the asset from assetsForMinify with no warning and no error.

Real builds in apps/tester-app, webpack 5.105.4, react-native webpack-bundle --platform ios --dev=false, config with no optimization.minimizer so Re.Pack's default runs (which is also the shape of templates/webpack.config.mjs):

terser-webpack-plugin in the project	main.jsbundle
5.5.0	1,969,176 bytes, mangled
5.6.1	4,846,598 bytes, `/******/ var self = self

And preferring the user's version is what triggers this rather than what protects against it. webpack itself depends on terser-webpack-plugin: ^5.3.17, so a plain npm i webpack@5.105.4 puts 5.6.1 at the project root today, and resolveTerserPluginCandidate([rootDir]) looks there first. Under pnpm nothing is hoisted, Re.Pack's own pinned 5.5.0 wins, and it works. An rspack-only npm project has no terser at the root at all, so webpack is the more exposed of the two.

Two things you may want before deciding on this PR:

1. I forced SwcJsMinimizerRspackPlugin on Rspack 1.6.0 with Re.Pack's test regex and it minified fine: 1,972,343 bytes in 2.51 s vs terser's 1,969,836 in 6.37 s, async chunk minified too. The comment in getMinimizerConfig.ts still points at the 1.5.0 regression from fix: use Terser for Rspack 1.5.0 and above temporarily #1273. That may already be unblocked, which would be your preferred direction. I did not run the app, so this is "produces minified output", not "verified at runtime".

2. There is a smaller fix than what this PR currently does. A plain function has no .filter property, so any version accepts the asset:

new TerserPlugin({
  test: /\.(js)?bundle(\?.*)?$/i,
  extractComments: false,
  minify: function repackTerserMinify(input, sourceMap, minimizerOptions, extractComments) {
    return require('terser-webpack-plugin').terserMinify(
      input, sourceMap, minimizerOptions, extractComments
    );
  },
  terserOptions: { format: { comments: false } },
})

I ran that with 5.6.1 in both the project and Re.Pack's own node_modules, so the default terser was a confirmed no-op and only the wrapper could do work: 1,969,176 bytes, byte identical to the 5.5.0 output. terserMinify is exported by 5.5.0 as well, and the wrapper is self contained so it survives worker serialization. It drops the capability probe, the fallback, and the warning.

Happy to rewrite #1444 as that wrapper, or to close it if you would rather fix the Rspack minimizer first and handle webpack separately.

[dannyhw]

I see, seems like i may have misunderstood the issue then. What do you propose as the right solution? I.e do you think what you mentioned in your comment (wrapper) is better or the solution presented in the pr already?

[giaBaoJS]

The wrapper, and I would rather rewrite this PR as that than merge what is here now.

What is here reacts to the symptom. It probes whether the installed plugin will refuse .bundle, then falls back to Re.Pack's own pinned copy and warns. It works, but it needs a capability probe, a fallback path and a warning string to do it, and the user ends up minifying with a different terser than the one in their lockfile.

The wrapper removes the condition instead. In 5.6.1 the dispatch is index.js:357:

if (typeof impl.filter !== "function" || ... impl.filter(name, info) !== false) {

so the filter is only consulted when the configured minify has one. Every built-in gets .filter assigned in utils.js, but a plain function does not, so passing our own named function makes every version from 5.5.0 up minify the asset, and the version that runs is the user's own. That is what "we prefer the user's version" was supposed to give them in the first place.

The judgement call worth saying out loud: we would be deliberately stepping around a filter the plugin author added. I think it is defensible here, since the doc comment on that option describes it as "return true when the minimizer supports the asset" and terser genuinely does support this asset. .bundle is JavaScript, and JS_FILE_RE is an extension heuristic rather than a capability test. But it is a call, not a fact, so it is yours to make rather than mine.

Say the word and I will rewrite it. If you would rather land the Rspack minimizer switch first and treat webpack on its own, I am equally happy to close this and open the wrapper as a separate small PR whenever it suits you.

[dannyhw]

@giaBaoJS ok that makes sense, sounds like the wrapper would be better. If you have the capacity that would be really great if you add those changes

[giaBaoJS]

Rewritten as the wrapper, pushed as a separate commit (878f75c) so the delta from the probe version is visible.

Against main the source change is now +20/-2 in getMinimizerConfig.ts: getTerserPlugin also returns the path it resolved, and getTerserConfig passes a minify. The probe, the fallback and the warning are gone.

apps/tester-app, --platform ios --dev=false, cache cleared between runs, terser-webpack-plugin swapped at the app root. Re-measured from scratch, not carried over from my earlier comment:

bundler	plugin	before	after
webpack	5.6.1	4,846,598	1,969,176
webpack	5.5.0	1,969,176	1,969,176
rspack	5.6.1	4,822,812	1,969,836
rspack	5.5.0	1,969,836	1,969,836

All four "after" bundles are byte-identical to their 5.5.0 baseline. __webpack_require__ occurrences go 6157 -> 50 on webpack and 6144 -> 46 on rspack and the /******/ var self = self || ... runtime banner is gone, so it is mangling and not just whitespace. The async chunk goes 728 -> 455 bytes, so *.chunk.bundle is covered by the test regex as well. 5.5.0 has no filter machinery at all (no impl.filter in dist/index.js, no JS_FILE_RE in dist/utils.js) and does export terserMinify, so the wrapper is a no-op there, which is what the identical 5.5.0 rows show.

Two things came out differently from the sketch in my earlier comment.

The wrapper cannot say require('terser-webpack-plugin') by name. It is serialized with serialize-javascript and re-evaluated in a worker (index.js:528 into minify.js transform), where require resolves from the plugin's own dist/, which is the correct copy. But with parallel off, or when getAvailableNumberOfCores returns 0, the same function runs in-process and require resolves from Re.Pack's dist/ instead. Under pnpm with a direct terser-webpack-plugin dependency those are two different copies, which is the same "not the terser in your lockfile" problem I was arguing against. So the resolved path is baked into the body:

new Function(
  `return function repackTerserMinify(input, sourceMap, minimizerOptions, extractComments) {
  return require(${JSON.stringify(pluginPath)}).terserMinify(input, sourceMap, minimizerOptions, extractComments);
}`
)()

new Function is there for the serialization constraint rather than for style: anything the wrapper closes over is gone by the time it runs, and it fails at runtime, not at build time. Checked both directions on a standalone webpack 5.105.4 + plugin 5.6.1 build. The wrapper logs isMainThread=false, so it really is going through a worker, and the closure-capturing variant fails with:

index.bundle from Terser plugin
TerserPlugin is not defined
ReferenceError: TerserPlugin is not defined
    at repackTerserMinify (eval at transform (node_modules/terser-webpack-plugin/dist/minify.js:328:3), <anonymous>:5:5)

getMinimizerVersion has to be carried across. The plugin folds it into the chunk hash (index.js:724) and Re.Pack builds with cache: { type: 'filesystem' } (getCommandConfig.ts:19), so a bare wrapper pins it to "0.0.0" and bumping terser stops invalidating the cache. One line copies it onto the wrapper; it does not bring filter along.

Tests rewritten. The old ones asserted which copy of the plugin got selected, which is machinery that no longer exists. The new ones put a fake project plugin through the same two steps the real one does, filter and then a toString() round trip through new Function, and assert the .bundle asset comes back minified. Reverting only getMinimizerConfig.ts to main and keeping the tests gives:

● getMinimizerConfig › should minify .bundle assets with a project plugin that only accepts .js
    - project(const answer = 40 + 2;
    + const answer = 40 + 2;

so it goes red because the asset comes back untouched, not because of a missing import.

The warning has nothing left to report, since every version now minifies. Changeset description updated to match.

[giaBaoJS]

@dannyhw wrapper is in. It replaces the version check, the fallback to the bundled copy and the warning, so nothing version specific is left in getMinimizerConfig.

Measured on apps/tester-app with terser-webpack-plugin@5.6.1 resolved at the app root: the iOS production bundle goes from 4,846,598 bytes unminified to 1,969,176 on webpack, and from 4,822,812 to 1,969,836 on Rspack.