bug#43549: 28.0.50; json-encode-string: Text is read-only

[Sam Steingold]

Evaluate the following in the *scratch* buffer of emacs -Q:

--8<---------------cut here---------------start------------->8---
(require 'json)
(setq s "asdf")
(put-text-property 1 2  'read-only t s)
(let ((json--long-string-threshold 0))
  (json-encode-string s))
--8<---------------cut here---------------end--------------->8---

the result is an error message

json-encode-string: Text is read-only


binding json--long-string-threshold to 0 merely disables an
optimization; another way to trigger an error is to start with a longer string.


In GNU Emacs 28.0.50 (build 2, x86_64-apple-darwin19.6.0, NS appkit-1894.60 
Version 10.15.6 (Build 19G2021))
 of 2020-09-21 built on BZ-C02XR5CGJG5L
Repository revision: d5d642eb71d8228d5a408a3d43ca1f4a5b500b9d
Repository branch: master
Windowing system distributor 'Apple', version 10.3.1894
System Description:  Mac OS X 10.15.6

Configured using:
 'configure --with-imagemagick --with-mailutils --with-ns
 
PKG_CONFIG_PATH=/usr/local/opt/libxml2/lib/pkgconfig:/usr/local/opt/imagemagick/lib/pkgconfig:/usr/local/opt/gnutls/lib/pkgconfig:/usr/local/opt/jansson/lib/pkgconfig:/usr/local/opt/libtiff/lib/pkgconfig:/usr/local/opt/libpng/lib/pkgconfig:/usr/local/opt/libjpeg/lib/pkgconfig:/usr/local/opt/freetype/lib/pkgconfig'

Configured features:
JPEG TIFF PNG IMAGEMAGICK NOTIFY KQUEUE ACL GNUTLS LIBXML2 ZLIB
TOOLKIT_SCROLL_BARS NS MODULES THREADS JSON PDUMPER LCMS2

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Messages

Minor modes in effect:
  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
  buffer-read-only: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny dired dired-loaddefs
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 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 time-date json
subr-x map seq byte-opt gv bytecomp byte-compile cconv help-fns
radix-tree cl-print debug backtrace help-mode easymenu find-func
cl-loaddefs cl-lib tooltip eldoc electric uniquify ediff-hook vc-hooks
lisp-float-type 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 elisp-mode lisp-mode
prog-mode register page tab-bar menu-bar rfn-eshadow isearch timer
select scroll-bar mouse jit-lock font-lock syntax facemenu 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 kqueue cocoa ns lcms2
multi-tty make-network-process emacs)

Memory information:
((conses 16 57583 6582)
 (symbols 48 7020 1)
 (strings 32 19982 1439)
 (string-bytes 1 653249)
 (vectors 16 12263)
 (vector-slots 8 170307 9852)
 (floats 8 29 99)
 (intervals 56 278 3)
 (buffers 992 14))

-- 
Sam Steingold (http://sds.podval.org/) on darwin Ns 10.3.1894
http://childpsy.net http://calmchildstories.com http://steingoldpsychology.com
http://islamexposedonline.com https://jihadwatch.org https://jij.org
The Politically Correct term for Censorship is Political Correctness.