Why is this a composer command? IMHO it should be a Symfony command (bin/console env:dump prod)

At least because we want to ship this for all Symfony versions without waiting for 4.3.

This seems a hack to me. If we go in that sens, we will move many code here.
I understand the reason, but I don't like the implementation :/
What about a symfony/backport ?

Of course I'm not strongly against this hack, but if we could find a better alternative, this will be much better

Please, not another package to maintain. If you want, you can provide a command to 4.3 and then we could deprecate this one. Personally, I don't think it's worth the effort. dump-autoload is a Composer command, so would be dump-env. Both are run at the same stage, looks consistent to me.

Thank you @renanbr.

I cannot understand the point of this at all. All it does is substitute the APP_ENV var for whatever name you specify (e.g. prod) and pretends that all other dev settings will somehow be suitable for that environment. That is almost never going to be the case, particularly if you have separate dev and production databases, which is fairly common. How are you expected to merge the rest of the production settings into this config, because this command doesn't appear to support that?

Edit: upon further inspection, it appears you are expected to produce either .env.prod or .env.prod.local, to override the dev defaults, but is this documented anywhere? The section specifically titled, Configuring Environment Variables in Production appears to make no reference to it whatsoever.