debug-code fails if hook doesn't exist

[John A Meinel]

If you run 'juju debug-hooks' then Juju will always trigger an event for every hook, whether or not it exists.
It was designed to do this so that someone debugging a charm could see that there is a lifecycle event, even if the hook isn't implemented, in case they want to actually start to implement it.
Which is fine, if a human tries to run './hooks/no-such-hook' then they get told it doesn't exist, and they can choose whether they want to exit 0 or exit 1 from the shell.

However, debug-code acts differently, in that it goes ahead and runs ./hooks/install (etc) so that the code being executed has a chance to actually run and grab an internal debugger.

However, if the charm doesn't implement a hook, then it gets a bad error that just keeps happening in the log:

unit-dummy-sink-0: 15:41:57 ERROR juju.worker.uniter.operation hook "source-relation-created" (via unknown/invalid hook handler) failed: exit status 1

An easy way to test it is

cd acceptancetests/repository/charms
juju deploy ./dummy-sink
juju deploy ./dummy-source

juju debug-code dummy-source/0

in another terminal
juju relate dummy-sink dummy-source

and you see 'source-relation-changed' errors like above (because source-relation-changed isn't implemented.

Actually, debug-hooks itself acts a bit silly, as it ends up printing:
3. To run an action or hook and end the debugging session avoiding processing any more events manually, use:

./

We should probably change the splash message a bit more if the hook is not implemented.

[Tim Penhey (thumper)]

https://github.com/juju/juju/pull/11527