Warn user to sync+rebuild on emacs' major version change

Byte-code is not generally compatible across major releases of Emacs,
and packages may have changed in that time. Best throw a more helpful
error than leave users to deal with the obscure errors that this can
cause.

core/cli/autoloads.el

@@ -32,7 +32,9 @@ one wants that.")
      (cl-check-type file string)
      (and (print! (start "Generating core autoloads..."))
           (doom-cli--write-autoloads
-           file (doom-cli--generate-autoloads
+           file
+           (doom-cli--generate-emacs-version-check)
+           (doom-cli--generate-autoloads
             (cl-loop for dir
                      in (append (list doom-core-dir)
                                 (cdr (doom-module-load-path 'all-p))
@@ -105,6 +107,12 @@ one wants that.")
                 (print! "M-x doom/restart")
                 (print! "M-x doom/reload")))
 
+(defun doom-cli--generate-emacs-version-check ()
+  `((unless (equal emacs-major-version (eval-when-compile emacs-major-version))
+      (signal 'doom-error
+              (list "Your installed (major) version of Emacs has changed"
+                    "Run 'doom sync && doom build' to bring Doom up to speed")))))
+
 (defun doom-cli--generate-var-cache (vars)
   `((setq ,@(cl-loop for var in vars
                      append `(,var ',(symbol-value var))))))

core/core-lib.el

@@ -101,6 +101,8 @@ Return t on success, nil otherwise (but logs a warning)."
       ;; `string-remove-suffix' is much cheaper (because it does no file sanity
       ;; checks during or after; just plain ol' string manipulation).
       (load (string-remove-suffix ".el" file) noerror 'nomessage)
+    (doom-error
+     (signal (car e) (cdr e)))
     ((debug error)
      (message "Autoload file error: %s -> %s" (file-name-nondirectory file) e)
      nil)))