Using Zsh, it doesn't show an error message when command not found

It works out-of-the-box in Ubuntu Xenial.

I've found the origin of the problem.

Since Zsh 5.3, the command_not_found_handler() behavior has changed, as you can see here:

https://github.com/zsh-users/zsh/blob/9e2afb92987d7fd96a838c15b6641cc1b634a825/README#L207-L214

Copy & paste:

  6) Previously, if the function command_not_found_handler was run
  in place of a command-not-found error, and the function returned
  non-zero status, zsh set the status to 127 and printed an error message
  anyway. Now, the status from the handler is retained and no additional
  message is printed. The main reasons for this change are that it was not
  possible to return a non-zero status to the parent shell from a command
  executed as a replacement, and the new implementation is more consistent
  with other shells.

So now, when you define a custom command_not_found_handler() function in Zsh, the shell never print an error message by itself, i.e., the error message must be printed by the handler function.

According to the above, I think the only solution is by remove the '--no-failure-msg' option from the /etc/zsh_command_not_found and therefore the command_not_found_handler() function is the only responsible to print error messages to the user.

It worked in Ubuntu Xenial because it ships Zsh 5.1 and the new behavior was introduced in Zsh 5.3.

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

The first line of the handler is also somewhat problematic. Namely:

[[ -x /usr/lib/command-not-found ]] || return 1

If command-not-found package is removed and this file is not, it will stop printing the message even if --no-failure-msg is removed.

Actually, maybe I spoke too soon: there's an if guarding the definition of the function at the top of that file.

Any news about this issue?

The bug is still reproducible with Ubuntu 19.04.

I raised the equivalent bug in Debian: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=927876

I have added the above patch to remove the --no-failure-message flag, which seems to fix the problem (I have also bumped compat and standards versions).
Please consider applying the patch and releasing a new version of the package.

The attachment "Remove --no-failure-message from zsh_command_not_found" seems to be a debdiff. The ubuntu-sponsors team has been subscribed to the bug report so that they can review and hopefully sponsor the debdiff. If the attachment isn't a patch, please remove the "patch" flag from the attachment, remove the "patch" tag, and if you are member of the ~ubuntu-sponsors, unsubscribe the team.

[This is an automated message performed by a Launchpad user owned by ~brian-murray, for any issue please contact him.]

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

Please submit this patch to Debian, where it will flow down to Ubuntu.

Unsubscribing the Ubuntu Sponsors Team.

Simon was a bit wrong, as the upstream situation is reversed, but either way, I guess it's me taking a look at it :)

@juliank is there any update on this bug? Did you ever get the chance to look at my patch?

Bump, @juliank !

Two years now since I submit this bug report. Any news?

Unfortunately not. @juliank seems to have gone incommunicado on this issue.
Since I have a patch that fixes this issue, would it be helpful to people if I make a PPA containing the patched command-not-found? Then at least there will be a solution for people until someone from Ubuntu eventually picks this up (which realistically isn't looking likely any time soon).

This bug was fixed in the package command-not-found - 20.10.0

---------------
command-not-found (20.10.0) groovy; urgency=medium

  * zsh: Do not pass --no-failure-msg, non-existing commands were not getting
    any output at all (LP: #1766068) (Closes: #927876)

 -- Julian Andres Klode <email address hidden> Mon, 01 Jun 2020 13:44:25 +0200

Thank you very much, juliank!

Could this fix be backported to 20.04?

The Eoan Ermine has reached end of life, so this bug will not be fixed for that release