bug#66742: 30.0.50; transient-mark-mode is not enabled after re-dumping Emacs

[Ihor Radchenko <yantar92@posteo.net>]

Gerd Möllmann <gerd.moellmann@gmail.com> writes:

> The list of custom-delayed-init-variables is built by function
> custom-initialize-delay. If you grep for that, you'll finds a number of
> declarations containing an :initialize with the delaying function.
>
> In a re-dumped Emacs, the variable is not a list, so nothing is done. In
> the particular case of transient-mark-mode, the default value, which is
> set in C, is nil, so it keeps that value.

Thanks for the analysis.
I dag a bit further and it looks like :initialize is used in
`define-minor-mode' and `defcustom' with the latter simply deferring
:initialize keyword processing to `defcustom'.

The :initialize keyword in `defcustom' is implicitly assumed to be
evaluated during Emacs startup, in the Emacs sessions that will use the
custom definition.

Actually, I think that I will not be wrong to say that (defvar foo
<value>. ..), (defcustom foo <value> ...), and similar expressions are
often assumed to evaluated in the same Emacs session that will use the
library. For example, Org mode often calculated default variable values
dynamically:

(defcustom org-clock-x11idle-program-name
  (if (executable-find "xprintidle")
      "xprintidle" "x11idle")
...)

Re-dumping such code is prone to subtle bugs when the dumping
environment differs from the runtime.

Things get worse when loading a library relies on side effects:

----- org-persist.el ---------
;; Point to temp directory when `org-persist--disable-when-emacs-Q' is set.
(when (and org-persist--disable-when-emacs-Q
           ;; FIXME: This is relying on undocumented fact that
           ;; Emacs sets `user-init-file' to nil when loaded with
           ;; "-Q" argument.
           (not user-init-file))
  (setq org-persist-directory
        (make-temp-file "org-persist-" 'dir)))
----------------------------

I suspect that it is only truly safe to re-dump parts of the libraries
that do not emit (byte-code ...) in the compiler output.

For example, the following is .elc part corresponding to the above
defcustom:

(defvar org-x11idle-exists-p (byte-code "\b\302>?\205%17\303\304\305	\"!\306=\205%17\303	!\306=\207" [system-type org-clock-x11idle-program-name (windows-nt ms-dos) call-process-shell-command format "command -v %s" 0] 4))#@46 Return the current X11 idle time in seconds.\x1f

The variable itself can be defined, but its value is (byte-code ...) and
thus should be evaluated during startup, and not dumped.

And the side-effect clause is a complete (byte-code ...):

(byte-code "\b\203%d	\204%d\303\304\305\"%12\306\307\n!!\310%1!\204%%0\211\306\311%3!!\211\262%3\232\203%12\312%1!\2044%0\313\314\n\"\266%2\202D%0\315\316\317\"\210\315\316\320\"\210\315\316\321\"\266%2\315\322\323\"\210\324\325!\207" [org-persist--disable-when-emacs-Q user-init-file org-persist-directory make-temp-file "org-persist-" dir directory-file-name file-name-as-directory file-exists-p file-name-directory file-writable-p message "Missing write access rights to org-persist-directory: %S" add-hook kill-emacs-hook org-persist-clear-storage-maybe org-persist-write-all org-persist-gc after-init-hook org-persist-load-all provide org-persist] 5)

-- 
Ihor Radchenko // yantar92,
Org mode contributor,
Learn more about Org mode at <https://orgmode.org/>.
Support Org development at <https://liberapay.com/org-mode>,
or support my work at <https://liberapay.com/yantar92>