Overriding $PATH in classic snap

[nottrobin]

I’m trying to run a Python module in a classic snap, and I’m running into a similar issue to the one encountered here:

Python classic snap confusion & frustration (core18, entry-point scripts, organize, stage, prime, override-build)

In trying to fix the build.snapcraft.io snap for the charm snap, I was getting some frustrating and inconsistent results, so I decided I’d pare it down to a minimal test case. I started with what’s in the broken branch of https://github.com/johnsca/python-snap-core18-test Essentially, it’s just a minimal Python app with a console_script entry-point called tst which prints some test output and also calls another entry-point script, tst-sub. Building that went without a hitch, but when calling …

That is, I get the following error:

$ dotrun --help
Traceback (most recent call last):
  File "/snap/dotrun/x6/bin/dotrun", line 6, in <module>
    from pkg_resources import load_entry_point
  File "/usr/local/lib/python3.6/dist-packages/pkg_resources/__init__.py", line 3252, in <module>
    @_call_aside
  File "/usr/local/lib/python3.6/dist-packages/pkg_resources/__init__.py", line 3236, in _call_aside
    f(*args, **kwargs)
  File "/usr/local/lib/python3.6/dist-packages/pkg_resources/__init__.py", line 3265, in _initialize_master_working_set
    working_set = WorkingSet._build_master()
  File "/usr/local/lib/python3.6/dist-packages/pkg_resources/__init__.py", line 584, in _build_master
    ws.require(__requires__)
  File "/usr/local/lib/python3.6/dist-packages/pkg_resources/__init__.py", line 901, in require
    needed = self.resolve(parse_requirements(requirements))
  File "/usr/local/lib/python3.6/dist-packages/pkg_resources/__init__.py", line 787, in resolve
    raise DistributionNotFound(req, requirers)
pkg_resources.DistributionNotFound: The 'canonicalwebteam.dotrun==0.0.0' distribution was not found and is required by the application

Presumably because the snap is using the host’s python3 binary, where I have installed my package into the snap’s python3 binary.

I tried overriding this with:

environment:
  PATH: $SNAP/bin:$SNAP/usr/bin:$SNAP/usr/local/bin:$PATH

But I still get the above error, even though if I actually shell into the snap I get the expected path and python3 binary, and the dotrun binary works:

robin@rt480:~/Projects/dotrun (python) $ which dotrun
/snap/bin/dotrun
robin@rt480:~/Projects/dotrun (python) $ dotrun --help
Traceback (most recent call last):
  File "/snap/dotrun/x6/bin/dotrun", line 6, in <module>
    from pkg_resources import load_entry_point
  File "/usr/local/lib/python3.6/dist-packages/pkg_resources/__init__.py", line 3252, in <module>
    @_call_aside
  File "/usr/local/lib/python3.6/dist-packages/pkg_resources/__init__.py", line 3236, in _call_aside
    f(*args, **kwargs)
  File "/usr/local/lib/python3.6/dist-packages/pkg_resources/__init__.py", line 3265, in _initialize_master_working_set
    working_set = WorkingSet._build_master()
  File "/usr/local/lib/python3.6/dist-packages/pkg_resources/__init__.py", line 584, in _build_master
    ws.require(__requires__)
  File "/usr/local/lib/python3.6/dist-packages/pkg_resources/__init__.py", line 901, in require
    needed = self.resolve(parse_requirements(requirements))
  File "/usr/local/lib/python3.6/dist-packages/pkg_resources/__init__.py", line 787, in resolve
    raise DistributionNotFound(req, requirers)
pkg_resources.DistributionNotFound: The 'canonicalwebteam.dotrun==0.0.0' distribution was not found and is required by the application
robin@rt480:~/Projects/dotrun (python) $ snap run --shell dotrun
robin@rt480:~/Projects/dotrun (python) $ echo $PATH
/snap/dotrun/x6/bin:/snap/dotrun/x6/usr/bin:/snap/dotrun/x6/usr/local/bin:/home/robin/.poetry/bin:/home/robin/.local/bin:/home/robin/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin:/home/robin/.cargo/bin:/home/robin/.cargo/bin:/home/robin/.cargo/bin
robin@rt480:~/Projects/dotrun (python) $ which dotrun
/snap/dotrun/x6/bin/dotrun
robin@rt480:~/Projects/dotrun (python) $ dotrun --help
usage: dotrun [-h] [-C DIRECTORY] [-s] [-e ENV] [command]

Containerized project-level dependency management and package.json commands

positional arguments:
  command               A package.json command to run with `yarn run XXX` inside dotrun.
                        Simply typing `dotrun` will run `yarn run start`.
                        
                        Or a special command - one of:
                        - version: Print the version
                        - exec [command]: Execute a command or open a bash shell within the dotrun context
                        - install: Reinstall node and python dependencies
                        - clean: Run `yarn run clean` and remove all dotrun files
                         (default: start)

optional arguments:
  -h, --help            show this help message and exit
  -C DIRECTORY, --directory DIRECTORY
                        The directory in which to run commands (default: current directory)
  -s, --skip-install    Don't check for python or node dependencies before running (default: False)
  -e ENV, --env ENV     Environment variables to use when running commands.
                        These will override what's in .env or .env.local

What have I done wrong? How can I change the $PATH for my dotrun command?