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* bug#54346: persist-save doesn't persist variables when the value is set to the default
@ 2022-03-12  1:15 Gulshan Singh
  2022-03-12 17:44 ` Lars Ingebrigtsen
  0 siblings, 1 reply; 10+ messages in thread
From: Gulshan Singh @ 2022-03-12  1:15 UTC (permalink / raw)
  To: 54346

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Calling (persist-save 'myvar) should persist the value of myvar to a
file. However, it doesn't do this if the value of myvar is the same as
the default value. See lines 135 and 136 of persist.el:
https://git.savannah.gnu.org/cgit/emacs/elpa.git/tree/persist.el?h=externals/persist&id=2a2f83b4d63734ed48603008c813cfacd9e99404#n135

The intention here could have been that there's no need to persist the
variable if the user doesn't change it from the default. But it leads
to a bug in the following case:

(require 'persist)
(persist-defvar myvar nil "docstring") ; #1
(persist-save 'myvar) ; #2
(setq myvar "foo")
(persist-save 'myvar) ; #3
(setq myvar nil)
(persist-save 'myvar) ; #4

At #1, the value of myvar is not persisted, which is fine. If myvar
was persisted in the past, that value would be loaded, otherwise (like
in my case), it will be set to nil.

At #2, explicitly calling persist-save does not persist myvar. This is
unexpected, but still not a bug: the in-memory value of myvar (nil) is
still equal to the default, and it is not persisted, so the next time
the code runs the default will be loaded again.

At #3, myvar is persisted. The value is now "foo", which is different
from the default value of "nil".

#4 is where the bug happens. The persisted value of myvar is "foo",
but the in-memory value of myvar is nil. We *should* persist the new
value here, so that on the next load of the symbol we get the latest
value. However, because the current in-memory value is equal to the
default value (nil), it's not persisted. The next time this code runs,
it will load "foo" as the value of myvar instead of nil.

One fix could be to remove the check to see if the value is set to the
default. Another could be that if the value is set to the default,
remove the persist file.

System information from report-emacs-bug:

In GNU Emacs 27.2 (build 1, x86_64-apple-darwin18.7.0, NS appkit-1671.60
Version 10.14.6 (Build 18G95))
 of 2021-11-18 built on builder10-14.lan
Windowing system distributor 'Apple', version 10.3.2113
System Description:  macOS 12.2.1

Configured using:
 'configure --with-ns '--enable-locallisppath=/Library/Application
 Support/Emacs/${version}/site-lisp:/Library/Application
 Support/Emacs/site-lisp' --with-modules'

Configured features:
NOTIFY KQUEUE ACL GNUTLS LIBXML2 ZLIB TOOLKIT_SCROLL_BARS NS MODULES
THREADS JSON PDUMPER GMP

Important settings:
  value of $LANG: en_US.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
  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

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny dired dired-loaddefs
format-spec rfc822 mml mml-sec password-cache epa derived epg epg-config
gnus-util rmail rmail-loaddefs text-property-search seq byte-opt gv
bytecomp byte-compile cconv mm-decode mm-bodies mm-encode mail-parse
rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045
ietf-drums mm-util mail-prsvr mail-utils persist ispell help-fns
radix-tree cl-print debug backtrace help-mode easymenu find-func
time-date subr-x 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
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cl-preloaded nadvice loaddefs button faces cus-face macroexp files
text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget hashtable-print-readable backquote threads kqueue cocoa ns
multi-tty make-network-process emacs)

Memory information:
((conses 16 52205 6991)
 (symbols 48 6523 1)
 (strings 32 17870 1009)
 (string-bytes 1 596696)
 (vectors 16 10502)
 (vector-slots 8 132509 11576)
 (floats 8 27 44)
 (intervals 56 378 4)
 (buffers 1000 13))

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^ permalink raw reply	[flat|nested] 10+ messages in thread

end of thread, other threads:[~2022-06-22  4:21 UTC | newest]

Thread overview: 10+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2022-03-12  1:15 bug#54346: persist-save doesn't persist variables when the value is set to the default Gulshan Singh
2022-03-12 17:44 ` Lars Ingebrigtsen
2022-04-09 21:45   ` Gulshan Singh
2022-04-10 12:17     ` Lars Ingebrigtsen
2022-04-10 19:36       ` Gulshan Singh
2022-04-11 10:18         ` Lars Ingebrigtsen
2022-06-21  2:14           ` Gulshan Singh
2022-06-21 10:49             ` Lars Ingebrigtsen
2022-06-22  0:55               ` Gulshan Singh
2022-06-22  4:21                 ` Lars Ingebrigtsen

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