GNU bug report logs - #3634
emacsclient: unwind-protect prevents printing final form

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Jonas Bernoulli <jonas <at> bernoul.li>
Subject: bug#3634: closed (Re: bug#3634: emacsclient: unwind-protect
 prevents printing final form)
Date: Tue, 12 Jul 2011 23:08:02 +0000

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Your bug report

#3634: emacsclient: unwind-protect prevents printing final form

which was filed against the emacs package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 3634 <at> debbugs.gnu.org.

-- 
3634: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=3634
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Glenn Morris <rgm <at> gnu.org>
To: 3634-done <at> debbugs.gnu.org
Subject: Re: bug#3634: emacsclient: unwind-protect prevents printing final form
Date: Tue, 12 Jul 2011 19:07:08 -0400

Stefan Monnier wrote:

> I'd expect that using condition-case to catch `quit' would work.
> Have you tried it?

Works for me.

STRING=$(emacsclient -e "(condition-case nil (read-string \"> \") (quit nil))")

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From: Jonas Bernoulli <jonas <at> bernoul.li>
To: bug-gnu-emacs <at> gnu.org
Subject: emacsclient: unwind-protect prevents printing final form
Date: Sun, 21 Jun 2009 03:43:12 +0200

Hi

I am trying to write a wrapper around emacsclient that would allow
emacs to be used by external applications to complete some string.

However it does not seem to be possible to
1. return the last form and
2. ensure that emacsclient always returns
at the same time.

(The following examples assumes default-minibuffer-frame exists. Just
remove the respective line if it doesn't.)

This works as long as the user does not abort:

#!/bin/bash
STRING=$(emacsclient -e "\
(select-frame-set-input-focus default-minibuffer-frame)
(read-string \"> \")"
echo ${STRING:1:$((${#STRING}-2))

But when he does, emacsclient never returns. So I tried using
unwind-protect to make sure that emacsclient always returns:

#!/bin/bash
STRING=$(emacsclient -e "\
(let ((emonad-client (car server-clients)))
  (select-frame-set-input-focus default-minibuffer-frame)
  (unwind-protect (read-string \"> \")
    (when (memq emonad-client server-clients)
      (server-delete-client emonad-client t))))")
echo ${STRING:1:$((${#STRING}-2))

Now my script always returns but fails to print the final form to
standard output even when input was NOT aborted.

I tried several things to work around this:

1. Store the return value of read-string in some variable, and using
the variable as last form of let. When I use (message "veni vedi %s"
tmp) as last form I can see that forms after unwind-protect are
actually evaluated, the last form's value is just never printed to
stout.
2. condition-case
3. catch

However in all cases nothing was printed to standard output. It seems
that as soon as some non-local exit is used emacsclient refuses to
print anything to stout. And since exit-minibuffer does (throw 'exit
nil) to abort minibuffer output there is now way to prevent such an
non-local exit.

As a workaround it might be possible to explicitly print to stout, but
I could not find any information on how to do that.

thx

Jonas

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