bug#56425: 28.1; post-command-hook is triggered on y-or-n-p

bug#56425: 28.1; post-command-hook is triggered on y-or-n-p

[Bhavin Gandhi]

Run emacs -Q and evaluate following code:

(defvar my-hook-counter)
(defun my-test-command ()
  (interactive)
  (message "my-test-command: setting post-command-hook")
  (setq my-hook-counter 3)
  (add-hook 'post-command-hook 'my-own-hook)
  (y-or-n-p "Some question: ")
  (message "my-test-command: message after setting the hook")
)
(defun my-own-hook ()
  (print (format "hook: this: %s, real: %s, last: %s" this-command
real-this-command last-command))
  (message "my-own-hook: hopefully executing at the end")
  (setq my-hook-counter (- my-hook-counter 1))
  (if (eq my-hook-counter 0)
      (remove-hook 'post-command-hook 'my-own-hook))
)

1. M-x my-test-command
2. Emacs is now waiting for the input in the minibuffer. And also the
   post-command-hook executes here.
   minibuffer] Some question: (y or n)  [my-own-hook: hopefully
executing at the end]
3. Answer y in the minibuffer.
   minibuffer] my-test-command: message after setting the hook

In the *Messages* buffer the sequence is:

--8<---------------cut here---------------start------------->8---
my-test-command: setting post-command-hook

"hook: this: my-test-command, real: my-test-command, last: keyboard-quit"

my-own-hook: hopefully executing at the end
^^^^^ unexpected execution of post-command-hook for my-test-command

Some question: (y or n) y
my-test-command: message after setting the hook

"hook: this: my-test-command, real: y-or-n-p-insert-y, last: my-test-command"

my-own-hook: hopefully executing at the end
--8<---------------cut here---------------end--------------->8---


When I run M-x my-test-command, the post-command-hook is executed while
Emacs is waiting for the user input (y-or-n-p) in the
minibuffer. And we get this in *Messages* buffer:

"hook: this: my-test-command, real: my-test-command, last: keyboard-quit"

My initial thought was that the y-or-n-p call is causing it.  Looking at
the code of y-or-n-p with my limited Elisp knowledge, it doesn't seems
to be an interactive function, and there aren't any calls to interactive
functions till it prints the message "Some question: " in
minibuffer. And, from the print statement this-command is
my-test-command and not y-or-n-p.

Also, my-test-command has not finished executing yet, it is waiting for
user input, so how does it trigger the post-command-hook?  I'm not able
to understand what causes it to trigger the post-command-hook, is it an
expected behavior? I'm I missing something here? Is read-from-minibuffer
triggering the post-command-hook?


In GNU Emacs 28.1 (build 1, x86_64-redhat-linux-gnu, GTK+ Version
3.24.31, cairo version 1.17.6)
 of 2022-05-12 built on 798eb2d274a4426aa2879373741c952d
Windowing system distributor 'The X.Org Foundation', version 11.0.12201002
System Description: Fedora Linux 36 (Workstation Edition)

Configured using:
 'configure --build=x86_64-redhat-linux-gnu
 --host=x86_64-redhat-linux-gnu --program-prefix=
 --disable-dependency-tracking --prefix=/usr --exec-prefix=/usr
 --bindir=/usr/bin --sbindir=/usr/sbin --sysconfdir=/etc
 --datadir=/usr/share --includedir=/usr/include --libdir=/usr/lib64
 --libexecdir=/usr/libexec --localstatedir=/var
 --sharedstatedir=/var/lib --mandir=/usr/share/man
 --infodir=/usr/share/info --with-dbus --with-gif --with-jpeg --with-png
 --with-rsvg --with-tiff --with-xft --with-xpm --with-x-toolkit=gtk3
 --with-gpm=no --with-xwidgets --with-modules --with-harfbuzz
 --with-cairo --with-json --with-native-compilation
 build_alias=x86_64-redhat-linux-gnu host_alias=x86_64-redhat-linux-gnu
 CC=gcc 'CFLAGS=-DMAIL_USE_LOCKF -O2 -flto=auto -ffat-lto-objects
 -fexceptions -g -grecord-gcc-switches -pipe -Wall
 -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2
 -Wp,-D_GLIBCXX_ASSERTIONS
 -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -fstack-protector-strong
 -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m64 -mtune=generic
 -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection'
 LDFLAGS=-Wl,-z,relro
 PKG_CONFIG_PATH=:/usr/lib64/pkgconfig:/usr/share/pkgconfig'

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GSETTINGS HARFBUZZ JPEG JSON
LIBOTF LIBSELINUX LIBSYSTEMD LIBXML2 M17N_FLT MODULES NATIVE_COMP NOTIFY
INOTIFY PDUMPER PNG RSVG SECCOMP SOUND THREADS TIFF TOOLKIT_SCROLL_BARS
X11 XDBE XIM XPM XWIDGETS GTK3 ZLIB

Important settings:
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Messages

Minor modes in effect:
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  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  buffer-read-only: t
  line-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr ispell dabbrev emacsbug message rmc puny dired
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term/common-win x-dnd tool-bar dnd fontset image regexp-opt fringe
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chinese composite emoji-zwj charscript charprop case-table epa-hook
jka-cmpr-hook help simple abbrev obarray cl-preloaded nadvice button
loaddefs faces cus-face macroexp files window text-properties overlay
sha1 md5 base64 format env code-pages mule custom widget
hashtable-print-readable backquote threads xwidget-internal dbusbind
inotify dynamic-setting system-font-setting font-render-setting cairo
move-toolbar gtk x-toolkit x multi-tty make-network-process
native-compile emacs)

Memory information:
((conses 16 73671 7615)
 (symbols 48 6866 0)
 (strings 32 20919 2083)
 (string-bytes 1 717484)
 (vectors 16 14470)
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-- 
Bhavin Gandhi (bhavin192) | https://geeksocket.in

bug#56425: 28.1; post-command-hook is triggered on y-or-n-p

[Juri Linkov]

> Is read-from-minibuffer triggering the post-command-hook?

This is the most interesting question.  When you replace the y-or-n-p call
in your code with read-from-minibuffer, do you see the same result?

If not, then maybe these lines y-or-n-p affect the behavior somehow,
but I'm sure:

  ;; Protect this-command when called from pre-command-hook (bug#45029)
  (this-command this-command)

If all fails, then as the last resort you always have an option to
fall back to the modal behavior of y-or-n-p by wrapping the call
with y-or-n-p-use-read-key:

  (let ((y-or-n-p-use-read-key t)) (y-or-n-p "Some question: "))

bug#56425: 28.1; post-command-hook is triggered on y-or-n-p

[Eli Zaretskii]

> From: Bhavin Gandhi <bhavin7392@gmail.com>
> Date: Wed, 6 Jul 2022 23:25:34 +0530
> 
> Also, my-test-command has not finished executing yet, it is waiting for
> user input, so how does it trigger the post-command-hook?  I'm not able
> to understand what causes it to trigger the post-command-hook, is it an
> expected behavior?

Yes.

> I'm I missing something here? Is read-from-minibuffer
> triggering the post-command-hook?

Yes.

Why are you surprised?  y-or-n-p invokes read-from-minibuffer, which
invokes recursive-edit, which starts a recursive command loop.  And
the command loop calls post-command-hook on each iteration.

bug#56425: 28.1; post-command-hook is triggered on y-or-n-p

[Lars Ingebrigtsen]

Eli Zaretskii <eliz@gnu.org> writes:

> Why are you surprised?  y-or-n-p invokes read-from-minibuffer, which
> invokes recursive-edit, which starts a recursive command loop.  And
> the command loop calls post-command-hook on each iteration.

When writing post-command-hook code, you have to be check whether you're
in the context you want to be (for instance, in the minubuffer or not).
I think it's always been this way, but these day we use the
read-from-minibuffer a lot more than we used to -- so y-or-n-p didn't
use to have this issue, but it does now.

But I think things are working as designed here, basically, so I'm
closing this bug report.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

bug#56425: 28.1; post-command-hook is triggered on y-or-n-p

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: Bhavin Gandhi <bhavin7392@gmail.com>,  56425@debbugs.gnu.org
> Date: Mon, 11 Jul 2022 12:54:26 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > Why are you surprised?  y-or-n-p invokes read-from-minibuffer, which
> > invokes recursive-edit, which starts a recursive command loop.  And
> > the command loop calls post-command-hook on each iteration.
> 
> When writing post-command-hook code, you have to be check whether you're
> in the context you want to be (for instance, in the minubuffer or not).
> I think it's always been this way, but these day we use the
> read-from-minibuffer a lot more than we used to -- so y-or-n-p didn't
> use to have this issue, but it does now.

Yes.  Code that wants to distinguish these cases from "normal"
post-command-hook invocations should examine the value of
minibuffer-depth, I think.