Re: PRINT_EXIT_VALUE: Suppress for if/while conditions

[Peter Stephenson <p.stephenson@samsung.com>]

On Fri, 31 Jul 2015 23:12:25 +0000
Daniel Shahaf <d.s@daniel.shahaf.name> wrote:
> I'd like to disable the effect of PRINT_EXIT_VALUE while evaluating
> if/while conditions, since it's uninformative (conditions sometimes
> fail, that's their sine qua non) and annoying (when doing a for/if
> interactively and the 'if' condition is false in many iterations, the
> option must be disabled to prevent stderr spamming).
> 
> So far I've got it working for builtins ("if false ; then : ; fi"
> doesn't warn, whereas in git tip it does), but not for external commands
> (with the patch, "if =false ; then : ; fi" still warns, but I'd like it
> not to warn).  This is related to the MONITOR option:
> 
>     % if =false ; then : ; fi
>     zsh: exit 1     =false
>     % unsetopt monitor
>     % if =false ; then : ; fi
>     %
> 
> I'm guessing that has something to do with printjob(), since it checks
> both 'jobbing' and opts[PRINTEXITVALUE], but I don't understand that
> function.  Could I get a hint, please?

It's a bit mysterious quite why it's implemented like that --- you might
have thought something parallel to ERREXIT would make more sense --- but
I don'e think what it actually does is that mysterious.  Bascially,
handling of printing exitvalues is divided into two parts: for anything
that runs within the shell it's done immediately the command is run; for
anything else it runs in printjob() when the job status changes (with
the side effect of dependence on MONITOR).  It might be done this way to
handle background jobs, which wouldn't be picked up if you did it in a
way more naturally related to the execution hierarchy.

But the intention is clearly that these are otherwise parallel cases.
So I think anything you do in the one case you can do in the other, as
you're proposing, up to asynchronous effects.

> Would it be correct to just slip a "&& !printexitvalue_depth" to the "if
> isset(PRINTEXITVALUE)" checks in printjob()?  I am not sure that would
> be correct in the synch=0 case.

Yes, I think you probably need something like

  (!printexitvalue_depth && sync == 1)

since the cases of calling it from jobs or bg or fg are irrelevant.

pws