Is --link the only option expected to be used by plugins at this stage not used by herokuish/buildstep? My first impression is that this fix is short-sighted but I'm also suffering from the issue so I'm happy if this works as a temporary fix.

What about dockerfile plugins that don't work for herokuish builds like --build-arg or --file?

Probably not and it is short-sighted indeed. However, leaving this broken is probably not good either.

EDIT: Also I don't follow what plugins you're referring to when you reference --build-arg or --file. Do you mean plugins that add those options?

Yeah I was just bringing up the inverse problem where a plugin is expecting a dockerfile deployment.

It does seem beneficial to tell the plugin which deployment type is happening to really solve this issue.

Updated to take into account the inverse problem. This is by no means exhaustive but gets us a pattern to filter args for now.

@michaelshobbs you want to add that static buildpack and a test app to herokuish?

I can yeah. My fork or the official one?

Your fork. Or just move your fork to the dokku org and be done with it. Official fork?

Yeah I'll revert this change here and open a new PR