Subject: bug#48839: 28.0.50; Emacs freezes and takes 100% CPU with C-h v l

From: Tassilo Horn <[email-masked]>
Date: Sat, 05 Jun 2021 00:01:59 +0200

I use the current Emacs master branch and the marginalia package which
adds annotations to completion, e.g., the truncated value and docstrings
of variables when completing a variable name.  When I do C-h v l
(describe-variable, starting completion with initial input "l"), Emacs
immediately gets stuck, takes 100% CPU, and will hang there
indefinitely.

I've made a C and Lisp backtrace using GDB, attached to this report.

I've played around a bit, and the issue happens when the variable
`load-history' is annotated.  At least I get the hang and 100% CPU also
when evaluating

  (marginalia-annotate-variable "load-history")

Looking at the marginalia code, I can see no evil, and indeed I can
un-marginaliarize the sample to

    (let ((print-escape-newlines t)
          (print-escape-control-characters t)
          (print-escape-multibyte t))
      (string-width (prin1-to-string load-history)))

which freezes my emacs in the same way.  Concretely, `prin1-to-string'
finishes and returns a 1.3 MB string and then `string-width' will run
indefinitely on that.  I've attached the prin1-ed value of my
load-history.

I can't reproduce that with emacs -Q where my load-history after startup
has just 139 entries rather than about 600 with my configured emacs.
For the same reason, I haven't been able to check if the problem is also
there with emacs 27 because my ~/.emacs is full of emacs 28 stuff.

Daniel, I've Cc'ed you just because you might be able to find some
workaround in marginalia.

In GNU Emacs 28.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.29, cairo version 1.17.4)
 of 2021-06-04 built on thinkpad-t440p
Repository revision: 7b50ed553faa6de6d51bf07d12d106ca61ab3ac4
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12101001
System Description: Arch Linux

Configured using:
 'configure --with-modules'

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
JSON LCMS2 LIBOTF LIBSYSTEMD LIBXML2 M17N_FLT MODULES NOTIFY INOTIFY
PDUMPER PNG RSVG SECCOMP SOUND THREADS TIFF TOOLKIT_SCROLL_BARS X11 XDBE
XIM XPM GTK3 ZLIB

Important settings:
  value of $LC_MONETARY: de_DE.utf8
  value of $LC_NUMERIC: de_DE.utf8
  value of $LC_TIME: de_DE.utf8
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Text

Minor modes in effect:
  global-aggressive-indent-mode: t
  diredfl-global-mode: t
  dynamic-completion-mode: t
  which-key-mode: t
  company-posframe-mode: t
  global-company-mode: t
  yas-global-mode: t
  yas-minor-mode: t
  global-git-commit-mode: t
  magit-auto-revert-mode: t
  vertico-mode: t
  marginalia-mode: t
  override-global-mode: t
  minibuffer-depth-indicate-mode: t
  recentf-mode: t
  pixel-scroll-mode: t
  save-place-mode: t
  savehist-mode: t
  show-paren-mode: t
  shell-dirtrack-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-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
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
~/Repos/el/mu/build/mu4e/mu4e hides ~/Repos/el/mu/mu4e/mu4e
~/Repos/el/mu/build/mu4e/mu4e-main hides ~/Repos/el/mu/mu4e/mu4e-main
~/Repos/el/mu/build/mu4e/mu4e-view hides ~/Repos/el/mu/mu4e/mu4e-view
~/Repos/el/mu/build/mu4e/mu4e-org hides ~/Repos/el/mu/mu4e/mu4e-org
~/Repos/el/mu/build/mu4e/mu4e-lists hides ~/Repos/el/mu/mu4e/mu4e-lists
~/Repos/el/mu/build/mu4e/mu4e-actions hides ~/Repos/el/mu/mu4e/mu4e-actions
~/Repos/el/mu/build/mu4e/mu4e-utils hides ~/Repos/el/mu/mu4e/mu4e-utils
~/Repos/el/mu/build/mu4e/mu4e-context hides ~/Repos/el/mu/mu4e/mu4e-context
~/Repos/el/mu/build/mu4e/mu4e-draft hides ~/Repos/el/mu/mu4e/mu4e-draft
~/Repos/el/mu/build/mu4e/mu4e-message hides ~/Repos/el/mu/mu4e/mu4e-message
~/Repos/el/mu/build/mu4e/mu4e-compose hides ~/Repos/el/mu/mu4e/mu4e-compose
~/Repos/el/mu/build/mu4e/mu4e-view-common hides ~/Repos/el/mu/mu4e/mu4e-view-common
~/Repos/el/mu/build/mu4e/mu4e-view-old hides ~/Repos/el/mu/mu4e/mu4e-view-old
~/Repos/el/mu/build/mu4e/mu4e-view-gnus hides ~/Repos/el/mu/mu4e/mu4e-view-gnus
~/Repos/el/mu/build/mu4e/mu4e-headers hides ~/Repos/el/mu/mu4e/mu4e-headers
~/Repos/el/mu/build/mu4e/mu4e-mark hides ~/Repos/el/mu/mu4e/mu4e-mark
~/Repos/el/mu/build/mu4e/mu4e-icalendar hides ~/Repos/el/mu/mu4e/mu4e-icalendar
~/Repos/el/mu/build/mu4e/mu4e-speedbar hides ~/Repos/el/mu/mu4e/mu4e-speedbar
~/Repos/el/mu/build/mu4e/mu4e-contrib hides ~/Repos/el/mu/mu4e/mu4e-contrib
~/Repos/el/mu/build/mu4e/mu4e-proc hides ~/Repos/el/mu/mu4e/mu4e-proc
~/Repos/el/mu/build/mu4e/mu4e-meta hides ~/Repos/el/mu/mu4e/mu4e-meta
~/Repos/el/mu/build/mu4e/mu4e-vars hides ~/Repos/el/mu/mu4e/mu4e-vars
/home/horn/.emacs.d/elpa/transient-20210530.2252/transient hides /home/horn/Repos/el/emacs/lisp/transient

Features:
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company-dabbrev-code company-dabbrev company-files company-clang
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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
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dynamic-setting system-font-setting font-render-setting cairo
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Memory information:
((conses 16 578262 70996)
 (symbols 48 44260 10)
 (strings 32 199185 6686)
 (string-bytes 1 6028236)
 (vectors 16 77469)
 (vector-slots 8 928820 30025)
 (floats 8 689 451)
 (intervals 56 1123 364)
 (buffers 992 16))