command-not-found does not tell users they need to use --class to install classic snaps

[Steve Langasek]

When looking at the transition from the awscli deb to the aws-cli snap, I noticed that the aws-cli snap is a classic snap.

This means that the command shown in command-not-found output does not actually work:

$ aws

Command 'aws' not found, but can be installed with:

sudo snap install aws-cli
sudo apt install awscli

See 'snap info aws-cli' for additional versions.

$ sudo snap install aws-cli
error: This revision of snap "aws-cli" was published using classic confinement
       and thus may perform arbitrary system changes outside of the security
       sandbox that snaps are usually confined to, which may put your system at
       risk.

       If you understand and want to proceed repeat the command including
       --classic.
$

It is not ideal that cut-and-pasting the shown command returns an error.

I am not sure that it is better to add the '--classic' flag to the commandline, since that also encourages users to cut and paste without necessarily understanding the implications of installing a classic snap.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[John Lenton (chipaca)]

As adding --classic has security implications, we want you to think about what it means, and only add it if you're ok with that. Actively discouraging cut-and-paste that'll open security holes.