GNU bug report logs - #79889
31.0.50; emacsclient -a "" no longer works as documented

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Package: emacs; Reported by: Richard Copley <rcopley@HIDDEN>; merged with #79913; dated Tue, 25 Nov 2025 20:28:05 UTC; Maintainer for emacs is bug-gnu-emacs@HIDDEN.
Merged 79889 79913. Request was from Eli Zaretskii <eliz@HIDDEN> to control <at> debbugs.gnu.org. Full text available.

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Date: Thu, 27 Nov 2025 12:27:31 +0000
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Subject: Re: bug#79889: 31.0.50; emacsclient with empty argument no longer
 starts emacs daemon
To: Eli Zaretskii <eliz@HIDDEN>
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On Thu, 27 Nov 2025 at 11:28, Eli Zaretskii <eliz@HIDDEN> wrote:
>
> The simple patch below should fix the problem.

Or this one:

diff --git a/lisp/server.el b/lisp/server.el
index ca6f9e2448b..7eca01d853a 100644
--- a/lisp/server.el
+++ b/lisp/server.el
@@ -1204,7 +1204,7 @@ server--process-filter-1
   (server-log (concat "Received " string) proc)
   ;; First things first: let's check the authentication
   (unless (process-get proc :authenticated)
-    (if (and (string-match "-auth \\([!-~]+\\)\n?" string)
+    (if (and (string-match "-auth \\([!-~]+\\)[ \n]?" string)
          (equal (match-string 1 string) (process-get proc :auth-key)))
     (progn
       (setq string (substring string (match-end 0)))

Either works for me.
Information forwarded to bug-gnu-emacs@HIDDEN:
bug#79889; Package emacs. Full text available.

Message received at 79889 <at> debbugs.gnu.org:


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Date: Thu, 27 Nov 2025 13:28:44 +0200
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From: Eli Zaretskii <eliz@HIDDEN>
To: Sean Whitton <spwhitton@HIDDEN>
In-Reply-To: <874iqfajju.fsf@HIDDEN> (message from Sean
 Whitton on Thu, 27 Nov 2025 09:53:09 +0000)
Subject: Re: bug#79889: 31.0.50;
 emacsclient with empty argument no longer starts emacs daemon
References: <CAPM58ohB1LVdXp5F2NND_DBmrJLYhwSK0q-UaWg-Sj3b4JZt1g@HIDDEN>
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> Cc: 79889 <at> debbugs.gnu.org
> From: Sean Whitton <spwhitton@HIDDEN>
> Date: Thu, 27 Nov 2025 09:53:09 +0000
> 
> On Mon 24 Nov 2025 at 07:17pm GMT, Richard Copley wrote:
> 
> > Recipe on Windows (I did not check if the same recipe works on Linux):
> > In a command prompt, run the following command, including the
> > two double-quote characters:
> >   emacsclientw -nca ""
> >
> > Expected behaviour: Emacs is started as a daemon (if an Emacs server is
> > not already running), and then a new frame is created.
> >
> > Actual behaviour: Emacs is started as a daemon (if an Emacs server is
> > not already running), and then the server prints "Unknown command:" to
> > its standard output, and emacsclientw.exe shows a message box,
> > ---------------------------
> > Emacsclient ERROR
> > ---------------------------
> > *ERROR*: Unknown command:
> > ---------------------------
> > OK
> > ---------------------------
> 
> Thanks.  This isn't reproducible here on GNU/Linux so I'm going to need
> someone on Windows to investigate further so that we can fix it.
> 
> Are empty command line arguments special on Windows, do you know?

This has nothing to do with empty arguments being special on Windows
(which they aren't).  Simply put, emacsclient is now completely broken
on Windows: even just "emacsclient SOME-FILE" fails with the same
"Unknown command" error.

The reason is this change:

  --- a/lisp/server.el
  +++ b/lisp/server.el
  @@ -1267,8 +1267,10 @@ server--process-filter-1
		  args-left)
	      ;; Remove this line from STRING.
	      (setq string (substring string (match-end 0)))
  -           (setq args-left
  -                 (mapcar #'server-unquote-arg (split-string request " " t)))
  +           (cl-assert (equal (substring request -1) " ")
  +                      nil "emacsclient request did not end in SPC")
  +           (setq args-left (mapcar #'server-unquote-arg
  +                                   (nbutlast (split-string request " "))))

Specifically, the fact that we now call split-string _without_ 3rd arg
non-nil, which means we don't remove empty strings from the result.
The immediate reason for the failure is that on MS-Windows the value
of 'request' starts with a leading SPC (because emacsclient sends an
additional command "-auth AUTH-STRING" at the beginning), and that
produces an empty string as the first element of args-left, since we
no longer remove empty strings.  server--process-filter-1 then barfs
on that empty string.

You don't see that problem on Unix because there's no leading -auth
command there.

The simple patch below should fix the problem.

However, I don't understand the logic of not removing empty strings
and the assumption that nbutlast will solve the problem: it sounds
like a fragile assumption to me, and the added cl-assert's seem to
indicate that you were also wary of that.  How can we be sure there
won't be other empty strings?  Can we come up with a cleaner solution?

diff --git a/lisp/server.el b/lisp/server.el
index ca6f9e2..eefdc39 100644
--- a/lisp/server.el
+++ b/lisp/server.el
@@ -1208,6 +1208,11 @@ server--process-filter-1
 	     (equal (match-string 1 string) (process-get proc :auth-key)))
 	(progn
 	  (setq string (substring string (match-end 0)))
+          ;; If "-auth STRING" is followed by a space, remove that
+          ;; space, to avoid having empty strings in args-left, which
+          ;; will then confuse the processing below.
+          (or (string-empty-p string)
+              (setq string (substring string 1)))
 	  (process-put proc :authenticated t)
 	  (server-log "Authentication successful" proc))
       (server-log "Authentication failed" proc)
Information forwarded to bug-gnu-emacs@HIDDEN:
bug#79889; Package emacs. Full text available.

Message received at 79889 <at> debbugs.gnu.org:


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From: Sean Whitton <spwhitton@HIDDEN>
To: Richard Copley <rcopley@HIDDEN>
Subject: Re: bug#79889: 31.0.50; emacsclient with empty argument no longer
 starts emacs daemon
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Date: Thu, 27 Nov 2025 09:53:09 +0000
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Hello,

On Mon 24 Nov 2025 at 07:17pm GMT, Richard Copley wrote:

> Recipe on Windows (I did not check if the same recipe works on Linux):
> In a command prompt, run the following command, including the
> two double-quote characters:
>   emacsclientw -nca ""
>
> Expected behaviour: Emacs is started as a daemon (if an Emacs server is
> not already running), and then a new frame is created.
>
> Actual behaviour: Emacs is started as a daemon (if an Emacs server is
> not already running), and then the server prints "Unknown command:" to
> its standard output, and emacsclientw.exe shows a message box,
> ---------------------------
> Emacsclient ERROR
> ---------------------------
> *ERROR*: Unknown command:
> ---------------------------
> OK
> ---------------------------

Thanks.  This isn't reproducible here on GNU/Linux so I'm going to need
someone on Windows to investigate further so that we can fix it.

Are empty command line arguments special on Windows, do you know?

This is what I would suggest for tracking down the problem:

- start Emacs normally, do M-x server-start
- use find-function to jump to server--process-filter-1
- use C-u C-M-x to instrument it
- execute emacsclientw.exe as you describe, step through
  server--process-filter-1 with Edebug to see what exactly gets sent and
  how it gets misprocessed.

-- 
Sean Whitton
Information forwarded to bug-gnu-emacs@HIDDEN:
bug#79889; Package emacs. Full text available.
Changed bug title to '31.0.50; emacsclient -a "" no longer works as documented' from '31.0.50; emacsclient with empty argument no longer starts emacs daemon' Request was from Richard Copley <rcopley@HIDDEN> to control <at> debbugs.gnu.org. Full text available.

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Subject: 31.0.50; emacsclient with empty argument no longer starts emacs daemon
To: bug-gnu-emacs@HIDDEN, spwhitton@HIDDEN
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Recipe on Windows (I did not check if the same recipe works on Linux):
In a command prompt, run the following command, including the
two double-quote characters:
  emacsclientw -nca ""

Expected behaviour: Emacs is started as a daemon (if an Emacs server is
not already running), and then a new frame is created.

Actual behaviour: Emacs is started as a daemon (if an Emacs server is
not already running), and then the server prints "Unknown command:" to
its standard output, and emacsclientw.exe shows a message box,
---------------------------
Emacsclient ERROR
---------------------------
*ERROR*: Unknown command:
---------------------------
OK
---------------------------

This happens since the following commit:

commit 68e337e630f8d0960cf971f066c27f315634bc39
Author: Sean Whitton <spwhitton@HIDDEN>
Date:   Fri Nov 7 12:33:21 2025 +0000

    Don't discard empty string arguments from emacsclient

    * lisp/server.el (server--process-filter-1): Don't discard empty
    string arguments from emacsclient.
    (server-eval-args-left):
    * doc/emacs/misc.texi (emacsclient Options):
    * etc/NEWS: Document the change.

Running emacsclient with the "-a" argument followed by an empty string
is documented in the Emacs manual, info node "emacsclient Options"
(41.3).


In GNU Emacs 31.0.50 (build 4, x86_64-w64-mingw32) of 2025-11-24 built
 on MACHINE
Repository revision: 68e337e630f8d0960cf971f066c27f315634bc39
Repository branch: HEAD
Windowing system distributor 'Microsoft Corp.', version 10.0.19045
System Description: Microsoft Windows 10 Pro (v10.0.2009.19045.6466)

Configured using:
 'configure
 PKG_CONFIG_PATH=/mingw64/lib/pkgconfig:/mingw64/share/pkgconfig'

Configured features:
ACL DBUS GIF GMP GNUTLS HARFBUZZ JPEG LCMS2 LIBXML2 MODULES NATIVE_COMP
NOTIFY W32NOTIFY PDUMPER PNG RSVG SOUND SQLITE3 THREADS TIFF
TOOLKIT_SCROLL_BARS TREE_SITTER WEBP XPM ZLIB

Important settings:
  value of $LANG: ENG
  locale-coding-system: cp1252

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  show-paren-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  minibuffer-nonselected-mode: t
  minibuffer-regexp-mode: t
  line-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr comp-run bytecomp byte-compile comp-common rx
emacsbug lisp-mnt message mailcap yank-media puny dired dired-loaddefs
rfc822 mml mml-sec password-cache epa derived epg rfc6068 epg-config
gnus-util text-property-search time-date subr-x mm-decode mm-bodies
mm-encode mailabbrev gmm-utils mailheader cl-loaddefs cl-lib sendmail
mail-parse rfc2231 rfc2047 rfc2045 ietf-drums mm-util mail-prsvr
mail-utils rmc iso-transl tooltip cconv eldoc paren electric uniquify
ediff-hook vc-hooks lisp-float-type elisp-mode mwheel touch-screen
dos-w32 ls-lisp term/w32-nt disp-table term/w32-win w32-win w32-vars
term/common-win tool-bar dnd fontset image regexp-opt fringe
tabulated-list replace newcomment text-mode lisp-mode prog-mode register
page tab-bar menu-bar rfn-eshadow isearch easymenu timer select
scroll-bar mouse jit-lock font-lock syntax font-core term/tty-colors
frame minibuffer nadvice seq simple cl-generic indonesian philippine
cham georgian utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao
korean japanese eucjp-ms cp51932 hebrew greek romanian slovak czech
european ethiopic indian cyrillic chinese composite emoji-zwj charscript
charprop case-table epa-hook jka-cmpr-hook help abbrev obarray oclosure
cl-preloaded button loaddefs theme-loaddefs faces cus-face macroexp
files window text-properties overlay sha1 md5 base64 format env
code-pages mule custom widget keymap hashtable-print-readable backquote
threads w32notify dbusbind w32 lcms2 multi-tty move-toolbar
make-network-process tty-child-frames native-compile emacs)

Memory information:
((conses 16 58380 17255) (symbols 48 6284 0) (strings 32 16688 1633)
 (string-bytes 1 477857) (vectors 16 9808)
 (vector-slots 8 144867 11048) (floats 8 24 5) (intervals 56 259 5)
 (buffers 1064 10))
Acknowledgement sent to Richard Copley <rcopley@HIDDEN>:
New bug report received and forwarded. Copy sent to bug-gnu-emacs@HIDDEN. Full text available.
Report forwarded to bug-gnu-emacs@HIDDEN:
bug#79889; Package emacs. Full text available.
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