This behavior was not modified by #38495: when the manifest file does not exist, the asset helper always throws an exception (already in 4.4).
If we are to change it, this is a new feature that should target 6.2.

Personally, I enable strict mode on all environments. So yes, the npm run build is required before running the tests or opening a page on dev environment.

What is the point of requiring webpack-encore-bundle in webapp-pack if running the webpack job is optional?

The webapp pack experience is plain broken right now, we cannot afford to wait for 6.2 to fix it.
Any alternative idea? Removing webpack encore from the pack?

/cc @weaverryan

An other alternative would be to create an empty manifest.json file 🙄.

But not installing webpack-encore-bundle by default would make easier to understand why npm/yarn is required.

I think we don't include Encore - so merge symfony/webapp-pack#7 . Running composer require encore is still very easy. And as @GromNaN said, you then know that you will need npm/yarn to run some other commands.

Even if try to include Encore, but without an error, it's not super useful. It would do nothing until you ran the npm/yarn commands. So if you already will need to run some commands, probably composer require encore isn't a big extra command to need to run :).

Closing in favor of symfony/webapp-pack#7