V6 upgrade cli error - Invalid options for dev server

[devsheva]

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Expected behavior:

Following the V6 upgrade guide to migrate from webpacker 5.x to 6.0.0rc should work fine when compiling assets and running dev-server

Actual behavior:

Trying to even launch the dev server command manually leads to this error.

npx webpack serve

[webpack-cli] Invalid options object. Dev Server has been initialized using an options object that does not match the API schema.
 - options has an unknown property '_assetEmittingPreviousFiles'. These properties are valid:
   object { allowedHosts?, bonjour?, client?, compress?, devMiddleware?, headers?, historyApiFallback?, host?, hot?, ipc?, liveReload?, onListening?, open?, port?, proxy?, server?, app?, setupExitSignals?, setupMiddlewares?, static?, watchFiles?, webSocketServer? }

Small, reproducible repo:

cannot easily provide unfortunately

Setup environment:

• Ruby version: 2.7.4
• Rails version: 6.1
• Webpacker version: 6.0.0rc6
• webpack: 5.96.1
• webpack-cli: 4.10.0
• webpack-dev-server 5.1.0

[devsheva]

I think i found the issue, webpack-cli v4 is not compatible with webpack-dev-server 5, and this is caused by this line which is causing the latest major install for dev server npm.

https://github.com/rails/webpacker/blob/a715e055d937748c7cfd34b0450295348ca13ee6/lib/install/template.rb#L85

[devsheva]

another problem i have now is that CSS is not getting loaded when using hmr