Classic snaps 'not found' if --classic argument is missing

[Stuart Bishop]

If the user forgets the '--classic' argument to 'snap install', then they get a confusing error message. I think the correct thing to do is inform the user that they need to give consent and use the --classic option to perform the install.

$ sudo snap install juju-act
error: cannot install "juju-act": snap not found

$ sudo snap install juju-act --classic
juju-act 1.0.0 from 'stub' installed

[John Lenton (chipaca)]

https://github.com/snapcore/snapd/pull/2710

[John Lenton (chipaca)]

That branch isn't the end of the work in this space, but it addresses this immediate issue. The error message still needs picking up by the client and presented to the user better, and some other operations that take --classic need similar work.