bug#45857: 28.0.50; Not possible to set package-user-dir in early-init.el

[Stefan Monnier <monnier@iro.umontreal.ca>]

>> the package-user-dir defcustom gets the custom-initialize-delay
>> intializer.  At least for me, this overrides any setting of
>> package-user-dir that is done in early-init.el.
> Oh, I see you're right, and I think this issue is wider than
> `package-user-dir` since it affects all the other vars that use
> `custom-initialize-delay`.

Back in June 2018, Eli wrote:
> I can see several ways out of this:
> 
>   . Move the call to custom-reevaluate-setting back where it was, and
>     instead call custom-reevaluate-setting in that earlier place only
>     for Info-default-directory-list, which was the original reason why
>     the call was moved;
>   . Add a call to custom-reevaluate-setting for blink-cursor-mode
>     where the window-system is already set up;
>   . Call custom-reevaluate-setting for all the delayed-init variables
>     twice: once where we do that now, and again where we did that
>     before the above commit;
>   . Introduce yet another variable similar to
>     custom-delayed-init-variables, but separate from it, and put on
>     it all the delayed-init variables that need the window-system to
>     be set up, leaving all the rest in custom-delayed-init-variables.

We ended up going with the 3rd option, but this is the source of the
problem here.  I think we should change to option 2 for now and plan on
fixing it for good by removing this exception, i.e. by making
the default value of `blink-cursor-mode` be t.

More concretely, I suggest the patch below,


        Stefan


diff --git a/lisp/startup.el b/lisp/startup.el
index 57fd87f20f..8c9ac4e30f 100644
--- a/lisp/startup.el
+++ b/lisp/startup.el
@@ -1311,12 +1312,13 @@ command-line
     (startup--setup-quote-display)
     (setq internal--text-quoting-flag t))
 
-  ;; Re-evaluate again the predefined variables whose initial value
-  ;; depends on the runtime context, in case some of them depend on
-  ;; the window-system features.  Example: blink-cursor-mode.
-  (let (current-load-list) ; c-r-s may call defvar, and hence LOADHIST_ATTACH
-    (mapc 'custom-reevaluate-setting custom-delayed-init-variables)
-    (setq custom-delayed-init-variables nil))
+  ;; Some vars's initialization need to be delayed yet further, until
+  ;; after we setup the real initial frame, because their initial
+  ;; value depends on the window-system features.
+  ;; Currently, the only such var is `blink-cursor-mode'.  See bug#30994.
+  ;; FIXME: We should arrange for `blink-cursor-mode's default to be
+  ;; unconditionally `t' so as to finally eliminate this problem.
+  (custom-reevaluate-setting 'blink-cursor-mode)
 
   (normal-erase-is-backspace-setup-frame)