Add minimal CLI

[stephenfin]

Add a minimal CLI interface that can be used as an alternative to build.

This clearly isn't complete: I'd like to see whether it's worth doing before I go any further.

[gaborbernat]

You'll need to add tests too, and I think we should add build_editable too via -e, --editable too.

[stephenfin]

I'm still not sure about the -e / --editable. Given we're not actually installing these things (that's the job of pip or something else), what value is there is generating them? From PEP-660:

An “editable” wheel uses the wheel format not for distribution but as ephemeral communication between the build system and the front end. This avoids having the build backend install anything directly. This wheel must not be exposed to end users, nor cached, nor distributed.

Should we really be exposing this?

[gaborbernat]

'm still not sure about the -e / --editable. Given we're not actually installing these things (that's the job of pip or something else), what value is there is generating them?

The main utility of this endpoint is for people to validate their build backend, and for that, I think it's useful.

[gaborbernat]

By the way what's your use case for this functionality?

[stephenfin]

By the way what's your use case for this functionality?

I was using it as a quick way to understand the pbr issues I was investigating in tox-dev/tox#2712. This gave me a realistic "user" of the sample frontend and helped me understand how it was all working. I figured if it helped me it would probably help others. In time, it would be nice to add a frontend that re-uses process like the Pep517VirtualEnvFrontend frontend in tox, since I suspect that's likely to highlight bugs in other build backends over time. This is still a good enough first pass though, IMO.