bug#63891: 29.0.91; customize-save-variable should not save all variables if a custom file exists

[Jimmy Wong]

This branch: https://github.com/emacs-mirror/emacs/blob/emacs-29/lisp/cus-edit.el#L1109

No it does not saves only one variable to file, it only saves one variable to file if you have only modified one variable.

As a matter of fact, custom-variable-save, custom-variable-mark-to-reset-standard, custom-face-save, custom-face-mark-to-reset-standard and custom-group-save all have the same problem. They all call custom-save-all and they all dump all modified customizable variable values on file without regard to whether it’s a single variable, face or a group the user asked Emacs to save.

On 4 Jun 2023 at 2:23 PM +0100, Eli Zaretskii <eliz@gnu.org>, wrote:

Date: Sun, 4 Jun 2023 14:02:55 +0100
From: Jimmy Wong <wyuenho@gmail.com>
Cc: 63891@debbugs.gnu.org

Yes sorry, I mean customize-save-variable, custom-save-variable doesn’t exist. There’s a branch in
customize-save-variable that saves all previously updated variables to the custom file if it exists.

I don't think I understand. customize-save-variable saves only a
single variable: the one whose name you type, with the value you type.
Which branch there does more, and how can you invoke that branch?

I just took a look at cus-edit.el, there appears to be no function that can surgically serialize just one
variable value to the custom file.

customize-save-variable is that function.