No way to natively build for the non-host arch

[Iain Lane]

installed: 3.6 (3059) 59MB classic

Just now I was trying to reproduce a snap build failure that happened on i386 but not amd64. This computer can natively run i386 code, VMs and containers, so I was hoping that snapcraft would let me do a native build. It couldn't :(.

I just filed a multipass bug (https://github.com/CanonicalLtd/multipass/issues/886) requesting `multipass launch bionic/i386` support, à la LXD. Basically I'm asking for snapcraft to support the same, i.e. the ability to do:

  $ snapcraft --arch=i386

and it'd launch an i386 VM or container.

I noticed also that `--use-lxd` hits cloud-images.ubuntu.com directly to get a minimal image, and only amd64 images are published there (see https://cloud-images.ubuntu.com/minimal/releases/bionic/release/). That means it's not possible to extend this method to support multiple arches, i.e. `snapcraft --arch=i386 --use-lxd` wouldn't work. The non-minimal images (https://cloud-images.ubuntu.com/releases/18.04/release/) have more arches. So I suppose to fix LXD properly we'd have to either switch to non-minimal images or convince the team to produce minimal for more arches.