fix: minify .bundle assets with terser-webpack-plugin 5.6.0 and newer - #1444

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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):

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.

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:

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:

●くろまる 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.