Incompatibility with compression-webpack-plugin in webpack 5

Library Affected: workbox-webpack-plugin

Browser & Platform:

## System:
 - OS: Linux 4.15 Linux Mint 19.1 (Tessa)
## Binaries:
 - Node: 10.16.0 - /usr/local/bin/node
 - Yarn: 1.22.5 - /usr/bin/yarn
 - npm: 6.9.0 - /usr/local/bin/npm

BUG: Compression happened before __WB_MANIFEST injection We use the InjectManifest module. After migrating to WebPack version 5, we noticed that the generated service-worker.js file is compressed by workbox-webpack-plugin before the injection of self.WB__MANIFETS happens. We guess that in the previous version, this file was delivered to this plugin after the injection phase, but in the current version, it is delivered after the file creation phase and before the injection, hence the compressed file Is incomplete.

webpack plugins

{
  plugins: [
    new WorkboxPlugin.InjectManifest({
      swSrc: './src/setup/sw.js',
      swDest: 'service-worker.js',
      exclude: [/\.(gz|br)$/],
    }),
    new CompressionPlugin({
      algorithm: 'gzip',
      minRatio: 0.8,
      test: /\.(js|css|html|svg)$/,
   })
  ]
}

package.json

{
  "webpack": "^5.4.0",
  "compression-webpack-plugin": "^6.1.0",
  "workbox-webpack-plugin": "^6.0.0-alpha.3",
}

[jeffposnick]

This should be fixed by upgrading to compression-webpack-plugin v6.1.1.

[jeffposnick]

Thanks for pointing this out.

After investigating a bit, changing this line in the compression-webpack-plugin’s source from compiler.hooks.compilation.tap to compiler.hooks.thisCompilation.tap seems to resolve the issue, without having to change any of the ordering of the stages.

When the compression plugin hooks into compilation instead of thisCompilation, I see that it’s compression logic runs twice—once for the child compilation created by InjectManifest (which results in the compression happening prior to the manifest injection), and then again following the manifest injection (which I think is a no-op, since that swDest file was already compressed). If I switch it to thisCompilation, then the compression only happens once, after the manifest injection has taken place.

I’m going to open an issue with the compression-webpack-plugin folks to investigate further, and see if switching to thisCompilation is the right approach for them to take.