bug#81510: 31.0.90; NS (macOS): clicking a disabled (:enable nil) tab-bar item crases Emacs

On Tue, Jul 28, 2026 at 11:31 AM Al Haji-Ali <[email protected]>
wrote:

>
> Clicking a tab-bar menu-item that has an explicit `:enable nil' property
> (i.e. a disabled item) crashes Emacs outright on the NS (macOS) port.
>
> Minimal recipe:
>
>     emacs -Q -l repro.el
>
> where repro.el contains:
>
>     (defun repro-tab-bar-format ()
>       '((disabled-item menu-item "disabled item -- click me" ignore
>          :enable nil)))
>     (setq tab-bar-format '(repro-tab-bar-format))
>     (tab-bar-mode 1)
>
> Then click on the "disabled item -- click me" text in the tab bar and
> note the crash.
>
> Backtrace (macOS crash report, Thread 0):
>
>     0   libsystem_kernel.dylib   __pthread_kill + 8
>     1   libsystem_pthread.dylib  pthread_kill + 296
>     2   libsystem_c.dylib        raise + 32
>     3   Emacs                    terminate_due_to_signal + 228
>     4   Emacs                    emacs_abort + 20
>     5   Emacs                    kbd_buffer_store_buffered_event + 652
>     6   Emacs                    ns_read_socket_1 + 112
>     7   Emacs                    gobble_input + 264
>     ...
>     -[EmacsView mouseDown:]
>
> Root cause, as far as I can tell from reading src/xdisp.c,
> src/keyboard.c and src/nsterm.m:
>
> 1. keyboard.c's parse_tab_bar_item defaults TAB_BAR_ITEM_ENABLED_P to t,
>    and an explicit `:enable FORM' property overrides it.
>
> 2. xdisp.c's handle_tab_bar_click returns nil on a disabled item, rather
>    than (Fcons (Qtab_bar, Qnil)) like a missed clicked.
>
> 3. nsterm.m's -[EmacsView mouseDown:] does:
>
>        if (!(tab_bar_p && NILP (tab_bar_arg)))
>          emacs_event->kind = MOUSE_CLICK_EVENT;
>        ...
>        EV_TRAILER (theEvent);
>
>    For a disabled item, emacs_event->kind is never assigned -- it's left
>    at its default, NO_EVENT. EV_TRAILER then calls
>    kbd_buffer_store_event_hold.
>
> 4. keyboard.c's kbd_buffer_store_buffered_event opens with:
>
>        if (event->kind == NO_EVENT)
>          emacs_abort ();
>
> I have not tested on X11/w32, so I am not sure if they have the same
> issue.
>
> Possible minimal fix: make handle_tab_bar_click's disabled-item
> branch return (Fcons (Qtab_bar, Qnil)) instead of bare Qnil, matching
> the "click missed" case, which nsterm.m (and presumably the other
> ports) already handle correctly as a harmless plain click. I haven't
> verified this doesn't have side effects for other callers of
> handle_tab_bar_click across the X11/w32 ports.
>
> ------------------
>
> In GNU Emacs 31.0.90 (build 1, aarch64-apple-darwin25.5.0, NS
>  appkit-2685.60 Version 26.5.1 (Build 25F80)) of 2026-07-12 built on
>  HW-R9XXWKPJ4D
> Windowing system distributor 'Apple', version 10.3.2685
> System Description:  macOS 26.5.2
>
> Configured using:
>  'configure --disable-dependency-tracking --disable-silent-rules
>  --enable-locallisppath=/opt/homebrew/share/emacs/site-lisp
>  --infodir=/opt/homebrew/Cellar/emacs-plus@31/31.0.90/share/info/emacs
>  --prefix=/opt/homebrew/Cellar/emacs-plus@31/31.0.90
>  --with-native-compilation=aot --with-xml2 --with-gnutls
>  --without-compress-install 'CFLAGS=-DFD_SETSIZE=10000
>  -DDARWIN_UNLIMITED_SELECT -I/opt/homebrew/opt/sqlite/include
>  -I/opt/homebrew/opt/gcc/include -I/opt/homebrew/opt/libgccjit/include'
>  --without-dbus --without-imagemagick --with-modules --with-rsvg
>  --with-webp --with-ns --disable-ns-self-contained
>  'LDFLAGS=-L/opt/homebrew/opt/sqlite/lib -L/opt/homebrew/lib/gcc/16
>  -Wl,-rpath,/opt/homebrew/lib/gcc/16''
>
> Configured features:
> ACL GIF GLIB GMP GNUTLS JPEG LCMS2 LIBXML2 MODULES NATIVE_COMP NOTIFY
> KQUEUE NS PDUMPER PNG RSVG SQLITE3 THREADS TIFF TOOLKIT_SCROLL_BARS
> TREE_SITTER WEBP XIM ZLIB
>
> Important settings:
>   value of $LANG: en_GB.UTF-8
>   locale-coding-system: utf-8-unix
>
> 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 term/ns-win ns-win
> ucs-normalize mule-util 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 kqueue cocoa ns lcms2
> multi-tty make-network-process tty-child-frames native-compile emacs)
>
> Memory information:
> ((conses 16 56258 9223) (symbols 48 6141 0) (strings 32 15274 1404)
>  (string-bytes 1 530642) (vectors 16 9719)
>  (vector-slots 8 134388 10017) (floats 8 22 2) (intervals 56 266 0)
>  (buffers 1064 10))
>

+ other people

Good catch.  At first glance, your proposal looks right.

diff --git a/src/xdisp.c b/src/xdisp.c
index 5377d5e8ada..81dcbb543be 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -15321,7 +15321,7 @@ handle_tab_bar_click (struct frame *f, int x, int
y, bool down_p,
   /* If item is disabled, do nothing.  */
   enabled_p = AREF (f->tab_bar_items, prop_idx + TAB_BAR_ITEM_ENABLED_P);
   if (NILP (enabled_p))
-    return Qnil;
+    return Fcons (Qtab_bar, Qnil);

   if (down_p)
     {

Let's see what others think.

-Stéphane