v9.4.0 webpack change - How to add custom ENV variables that depends on the buildId?

Bug report

Describe the bug

Back in <v9.4, I was doing the following to augment my env variables in next.config.js:

webpack: (config, { isServer, buildId }) => {
    const APP_VERSION_RELEASE = `${packageJson.version}_${buildId}`;

    // Dynamically add some "env" variables that will be replaced during the build
    config.plugins[1].definitions['process.env.APP_RELEASE'] = JSON.stringify(buildId);
    config.plugins[1].definitions['process.env.APP_VERSION_RELEASE'] = JSON.stringify(APP_VERSION_RELEASE);

    if (isServer) { // Trick to only log once
      console.debug(`[webpack] Building release "${APP_VERSION_RELEASE}"`);
    }
  ...
}

I just upgraded to v9.4.0 and now the server crashes with TypeError: Cannot set property 'process.env.APP_RELEASE' of undefined.

After logging things a bit, I noticed the webpack function is executed twice, and doesn’t have the same plugins attached between attempts. The result is that once holds DefinePlugin at index 2, and the second time, the index is DefinePlugin.

This is a regression in behaviour, but maybe the way I do things isn’t the recommended one?

To Reproduce

Use v9.4.0

Attempt to write config.plugins[2].definitions['process.env.APP_RELEASE'] = 'test' in webpack function

Expected behavior

It should keep the same plugins order between calls.

[nandorojo]

@timer is @magus’s solution valid here? I’d like to have my unique build ID in my app for analytics and such. We’re trying to trace down some bugs that users have had, but it’s hard to know if they’re solved for certain people when we’re pushing 10x per day.

Thanks!

[magus]

For anyone discovering this issue and needing a more robust solution, this is working for me.

Before

config.plugins.push(
  new webpack.DefinePlugin({
    __DEV__: JSON.stringify(EnvConfig.DEV),
    'process.env.SENTRY_RELEASE': JSON.stringify(buildId),
  }),
);

After

config.plugins.forEach((plugin) => {
  if (plugin.constructor.name === 'DefinePlugin') {
    plugin.definitions = {
      ...plugin.definitions,
      __DEV__: JSON.stringify(EnvConfig.DEV),
      'process.env.SENTRY_RELEASE': JSON.stringify(buildId),
    };
  }
});