ubuntu-image not working when libs are not installed as debs

hmm, this seems to not only be libs ...

Fetching core
Fetching pc-kernel
Fetching pc
Crash in state machine
Traceback (most recent call last):
  File "/snap/ubuntu-image/59/lib/python3.5/site-packages/ubuntu_image/__main__.py", line 204, in main
    list(state_machine)
  File "/snap/ubuntu-image/59/lib/python3.5/site-packages/ubuntu_image/state.py", line 82, in __next__
    step()
  File "/snap/ubuntu-image/59/lib/python3.5/site-packages/ubuntu_image/builder.py", line 357, in prepare_filesystems
    self._prepare_one_volume(i, name, volume)
  File "/snap/ubuntu-image/59/lib/python3.5/site-packages/ubuntu_image/builder.py", line 309, in _prepare_one_volume
    label_option, part_img))
  File "/snap/ubuntu-image/59/lib/python3.5/site-packages/ubuntu_image/helpers.py", line 91, in run
    **args)
  File "/snap/ubuntu-image/59/usr/lib/python3.5/subprocess.py", line 693, in run
    with Popen(*popenargs, **kwargs) as process:
  File "/snap/ubuntu-image/59/usr/lib/python3.5/subprocess.py", line 947, in __init__
    restore_signals, start_new_session)
  File "/snap/ubuntu-image/59/usr/lib/python3.5/subprocess.py", line 1551, in _execute_child
    raise child_exception_type(errno_num, err_msg)
FileNotFoundError: [Errno 2] No such file or directory: 'mkfs.vfat'

Ok, it seems that the 'classic' snap confinement works a bit differently than we expected, it's much less sophisticated. The problem here is that the snap contains all the required libraries and executables, but I noticed that the library search paths when running classic snapped applications does not include any of the snappy paths. e.g. the libparted that's installed in the /snap snap's directory is simply not visible to python3-parted from the snap as it only looks for libraries on the main rootfs. Oliver mentioned that it's a known 'feature' of classic confinement and if we want to use the snap directory libraries we'd have to hack up the snap wrappers to modify LD_LIBRARY_PATH during execution. To me this sounds like a very naughty thing to do.

All this rises some concerns about continuing to use classic confinement as it looks like a very very hacky thing. I assumed that it's more 'mature' but it's actually not. IMO if we need to resort to things like this this would simply mean we're not really a good classic snap after all.

https://github.com/snapcore/snapcraft/blob/master/bin/snapcraft-classic is an example of such a wrapper.

After some discussion with Steve, it seems we still want to stay as a classic snap - I have a branch underway that has the wrapper in place. Need to test it before getting it merged.

This bug has already been released in the snap re-release, 1.0+snap4.