bug#45708: 27.1; (setq inhibit-default-init t) not working

[Eli Zaretskii]

> From: Leo Liu <sdl.web@gmail.com>
> Date: Thu, 07 Jan 2021 13:34:22 +0800
> 
> I tried to move to 27.1 in Oct 2020 but my setup was badly broken.
> 
> So I tried again today and I discovered the culprit seemed to be that
> default.el is loaded regardless of (setq inhibit-default-init t) in my
> emacs init file.
> 
> My emacs setup has been working flawlessly since at least Emacs 24.
> 
> This incompatibility seems unintentional because the elisp documentation
> specifically allows setting inhibit-default-init in user init file.

Yes, this is an unintended consequence of refactoring some of the
startup code to support the early-init file.

Does the patch below fix the problem?

diff --git a/lisp/startup.el b/lisp/startup.el
index cdf4eea..b60c13e 100644
--- a/lisp/startup.el
+++ b/lisp/startup.el
@@ -927,7 +927,8 @@ startup--load-user-init-file
 loaded, and ALTERNATE-FILENAME-FUNCTION is non-nil, then it is
 called with no arguments and should return the name of an
 alternate init-file to load.  If LOAD-DEFAULTS is non-nil, then
-load default.el after the init-file.
+load default.el after the init-file, unless `inhibit-default-init'
+is non-nil.
 
 This function sets `user-init-file' to the name of the loaded
 init-file, or to a default value if loading is not possible."
@@ -983,8 +984,8 @@ startup--load-user-init-file
                     (sit-for 1))
                   (setq user-init-file source))))
 
-            (when load-defaults
-
+            (when (and load-defaults
+                       (not inhibit-default-init))
               ;; Prevent default.el from changing the value of
               ;; `inhibit-startup-screen'.
               (let ((inhibit-startup-screen nil))
@@ -1390,7 +1391,7 @@ command-line
        (expand-file-name
         "init"
         startup-init-directory))
-     (not inhibit-default-init))
+     t)
 
     (when (and deactivate-mark transient-mark-mode)
       (with-current-buffer (window-buffer)