bug#48812: 28.0.50; describe-bindings stucks and gets high CPU load

[Naofumi Yasufuku]

Attached simple patch could fix this.
Is there no regression with this change?

Regards,
—Naofumi

0001-Fix-describe-bindings-stuck-caused-by-heavy-shadow_l.patch
Description: Binary data

> On Jun 4, 2021, at 0:06, Naofumi Yasufuku <naofumi@yasufuku.dev> wrote:
> 
> This describe-bindings stuck is caused by millions of shadow_lookup() calls
> in src/keymap.c describe_vector().
> 
> ------------------------------------------------------------------------
> $ ./src/emacs
> describe_vector] shadow_lookup loop START: definition=self-insert-command 
> shadowed_by=nil starting_i=128 i=4194175
> describe_vector] shadow_lookup loop END:   definition=self-insert-command 
> shadowed_by=nil starting_i=128 i=4194175
> describe_vector] shadow_lookup loop START: definition=self-insert-command 
> shadowed_by=nil starting_i=4194176 i=4194303
> describe_vector] shadow_lookup loop END:   definition=self-insert-command 
> shadowed_by=nil starting_i=4194176 i=4194303
> describe_vector] shadow_lookup loop START: definition=digit-argument 
> shadowed_by=nil starting_i=48 i=57
> describe_vector] shadow_lookup loop END:   definition=digit-argument 
> shadowed_by=nil starting_i=48 i=57
> $ 
> ------------------------------------------------------------------------
> diff --git a/src/keymap.c b/src/keymap.c
> index fb8eceaec1..0efa78ce9b 100644
> --- a/src/keymap.c
> +++ b/src/keymap.c
> @@ -3065,6 +3065,11 @@ describe_vector (Lisp_Object vector, Lisp_Object 
> prefix, Lisp_Object args,
>        if (CHAR_TABLE_P (vector) && i != starting_i)
>       {
>         Lisp_Object key = make_nil_vector (1);
> +       fprintf (stderr, "%s] shadow_lookup loop START: definition=%s 
> shadowed_by=%s starting_i=%d i=%d\n",
> +                __func__,
> +                SDATA (SYMBOL_NAME (definition)),
> +                SDATA (SYMBOL_NAME (shadowed_by)),
> +                starting_i, i);
>         for (int j = starting_i + 1; j <= i; j++)
>           {
>             ASET (key, 0, make_fixnum (j));
> @@ -3072,6 +3077,11 @@ describe_vector (Lisp_Object vector, Lisp_Object 
> prefix, Lisp_Object args,
>             if (NILP (Fequal (tem, shadowed_by)))
>               i = j - 1;
>           }
> +       fprintf (stderr, "%s] shadow_lookup loop END:   definition=%s 
> shadowed_by=%s starting_i=%d i=%d\n",
> +                __func__,
> +                SDATA (SYMBOL_NAME (definition)),
> +                SDATA (SYMBOL_NAME (shadowed_by)),
> +                starting_i, i);
>       }
>  
>        /* If we have a range of more than one character,
> ------------------------------------------------------------------------
> 
> 
> This shadow_lookup() loop was introduced by the following commit:
> 
> ------------------------------------------------------------------------
> commit a6490343366f2b2331a91dcb693effb3a9dd78f5
> Author: Stefan Kangas <stefan@marxist.se>
> Date:   Fri Nov 13 15:28:29 2020 +0100
> 
>     Don't show key ranges if shadowed by different commands
> 
>     * src/keymap.c (describe_vector): Make sure found consecutive keys
>     are either not shadowed or, if they are, that they are shadowed by
>     the same command.  (Bug#9293)
>     * test/src/keymap-tests.el
>     (help--describe-vector/bug-9293-one-shadowed-in-range): New test.
> 
> ------------------------------------------------------------------------
> 
> 
> <28.0.50-describe-bindings-01.png>
> 
> <28.0.50-describe-bindings-02.png>
> 
> <27.1-ubuntu-describe-bindings.png>
> 
> 
> In GNU Emacs 28.0.50 (build 3, aarch64-unknown-linux-gnu, GTK+ Version 
> 3.24.25, cairo version 1.16.0)
>  of 2021-06-03 built on phoebe
> Repository revision: 089e0c4c55dcf72f9cf2f6f04b8a52fc7355499c
> Repository branch: master
> Windowing system distributor 'The X.Org Foundation', version 11.0.12101001
> System Description: Ubuntu 21.04
> 
> Configured features:
> CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG JSON
> LCMS2 LIBSELINUX LIBSYSTEMD LIBXML2 MODULES NOTIFY INOTIFY PDUMPER PNG
> RSVG SECCOMP SOUND THREADS TIFF TOOLKIT_SCROLL_BARS X11 XDBE XIM XPM
> GTK3 ZLIB
> 
> Important settings:
>   value of $LANG: en_US.UTF-8
>   value of $XMODIFIERS: @im=ibus
>   locale-coding-system: utf-8-unix
> 
> Major mode: C/*l
> 
> Minor modes in effect:
>   bug-reference-prog-mode: t
>   tooltip-mode: t
>   global-eldoc-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
>   auto-composition-mode: t
>   auto-encryption-mode: t
>   auto-compression-mode: t
>   line-number-mode: t
>   transient-mark-mode: t
>   abbrev-mode: t
> 
> Load-path shadows:
> None found.
> 
> Features:
> (shadow sort mail-extr emacsbug message rmc puny rfc822 mml mml-sec epa
> derived epg epg-config gnus-util rmail rmail-loaddefs auth-source cl-seq
> eieio eieio-core cl-macs eieio-loaddefs password-cache json map
> text-property-search mm-decode mm-bodies mm-encode mail-parse rfc2231
> mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums
> mm-util mail-prsvr mail-utils vc-git diff-mode easy-mmode vc
> vc-dispatcher bug-reference cc-mode cc-fonts cc-guess cc-menus cc-cmds
> cc-styles cc-align cc-engine cc-vars cc-defs misearch multi-isearch
> dired-aux dired dired-loaddefs time-date subr-x cl-extra seq byte-opt gv
> bytecomp byte-compile cconv kmacro two-column help-mode cl-loaddefs
> cl-lib iso-transl tooltip eldoc electric uniquify ediff-hook vc-hooks
> lisp-float-type mwheel term/x-win x-win term/common-win x-dnd tool-bar
> dnd fontset image regexp-opt fringe tabulated-list replace newcomment
> text-mode elisp-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 cl-generic
> 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 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 dbusbind
> inotify lcms2 dynamic-setting system-font-setting font-render-setting
> cairo move-toolbar gtk x-toolkit x multi-tty make-network-process emacs)
> 
> Memory information:
> ((conses 16 118009 7881)
>  (symbols 48 9308 1)
>  (strings 32 27924 2053)
>  (string-bytes 1 1038142)
>  (vectors 16 18491)
>  (vector-slots 8 227657 9510)
>  (floats 8 31 163)
>  (intervals 56 10630 0)
>  (buffers 992 14))
> 
>