refuse to build if no environment matches #1507
Description
Proposed change
I'm proposing that we should fail to build if the repo has no environment specification.
Currently, we populate an image with our default 'base' environment and the repo contents. This technically can make sense and can be used for standard-library-only repos of notebooks. But most of the cases I've seen on e.g. mybinder.org are random repos launched for abuse. I haven't seen any repos that are launched for legitimate use without any environment specifications (that doesn't mean they exist and don't make sense).
Alternative options
Don't do this!
Who would use this feature?
mybinder.org and other Binder deployments limiting abuse
How much effort will adding it take?
Not much. We would need to change the detect logic for the last fallback buildpack to not return True unconditionally.
Who can do this work?
Anyone!