Add --exit-code to make install --dry-run return non-zero when packages would be installed

[flying-sausages]

Fixes #13802

• Changes the return code in case the dry-run indicates that some changes would be made

[flying-sausages]

Should this get some tests?

[notatallshaw]

Sorry, I misread your request, I was thinking you were asking for when dry run fails.

If it succeeds but would install something I don't think that should be non-zero.

But I do agree it would be good to programmatically tell the difference, I think it might be possible by using an installation report, I will try and look later today after work.

[flying-sausages]

The amount of tests failing suggest that there's a precedent with the expectation that this will continue working as is.

I still do think there's value in having a non-zero return for a dry-run which reports changes, would it be an option to add an extra flag such as --exit-code to enable this behaviour, and change the exit code to either 65 or 79 so it can be distinguished from an actual error? This would keep the existing interface working as is, and make it

[notatallshaw]

Unfortunately I don't think this use case warrants yet another flag, and like our tests users might be dependent on our exit codes.

If we did decide this required special exit code behavior I would rather go through a deprecation cycle where we warn users that we are going to change the behavior. And I don't think this use case warrants that either.

In the mean time see my example of implementing this programmatically with existing tools: #13802 (comment). In fact, I might switch our tests to use this.

[flying-sausages]

Hmm I see. Makes sense.