refactor: make early-init.el Doom's universal bootstrapper

This centralizes Doom's core startup optimizations and, as a
side-effect, reduces the runtime of bin/doom commands substantially.
This also simplifies the user story for loading Doom remotely (for batch
sessions or doomscripts).

bin/doom

@@ -74,19 +74,20 @@
 ;; - The user may have a noexec flag set on /tmp, so pass the exit script to
 ;;   /bin/sh rather than executing them directly.
 
-;; Ensure Doom runs out of this file's parent directory (or $EMACSDIR), where
-;; Doom is presumably installed.
-(setq user-emacs-directory
-      (if (getenv-internal "EMACSDIR")
-          (file-name-as-directory
-           (file-truename (getenv-internal "EMACSDIR")))
-        (expand-file-name
-         "../" (file-name-directory (file-truename load-file-name)))))
-
-
-;;
-;;; Sanity checks
+;; Doom's core sets up everything we need; including `doom-*-dir' variables,
+;; universal defaults, and autoloads for doom-*-initialize functions.
+(condition-case e
+    (let ((load-prefer-newer t))
+      (load (expand-file-name
+             "../early-init" (file-name-directory (file-truename load-file-name)))
+            nil 'nomessage))
+  ;; Prevent ugly backtraces for trivial errors
+  (user-error (message "Error: %s" (cadr e))
+              (kill-emacs 2)))
 
+;; UX: Abort if the user is using 'doom' as root, unless ~/.emacs.d is owned by
+;; root, in which case we assume the user genuinely wants root to be their
+;; primary user account for Emacs.
 (when (equal (user-real-uid) 0)
   ;; If ~/.emacs.d is owned by root, assume the user genuinely wants root to be
   ;; their primary user, otherwise complain.
@@ -104,16 +105,6 @@
     (kill-emacs 2)))
 
 
-;;
-;;; Load Doom's CLI framework
-
-(require 'doom-cli (expand-file-name "lisp/doom-cli" user-emacs-directory))
-
-;; Load $DOOMDIR/init.el, to read the user's `doom!' block, and so users can
-;; customize things early, if they like.
-(load! doom-module-init-file doom-user-dir t)
-
-
 ;;
 ;;; Entry point
 
@@ -237,7 +228,12 @@ SEE ALSO:
 
 
 ;;
-;;; Commands
+;;; Load user config + commands
+
+;; Load $DOOMDIR/init.el, to read the user's `doom!' block and give users an
+;; opportunity to customize the CLI environment, if they like. Otherwise, they
+;; can do so in .doomrc or .doomproject.
+(load! doom-module-init-file doom-user-dir t)
 
 (let ((dir (doom-path doom-core-dir "cli")))
   ;; It'd be simple to just load these files directly, but because there could

early-init.el

@@ -24,9 +24,12 @@
 ;; stuttering/freezes.
 (setq gc-cons-threshold most-positive-fixnum)
 
-;; Prioritize old byte-compiled source files over newer sources. It saves us a
-;; little IO time to skip all the mtime checks on each lookup.
-(setq load-prefer-newer nil)
+(eval-and-compile
+  ;; PERF: Don't use precious startup time checking mtime on elisp bytecode.
+  ;;   Ensuring correctness is 'doom sync's job, not the interactive session's.
+  ;;   Still, stale byte-code will cause *heavy* losses in startup efficiency.
+  (setq load-prefer-newer noninteractive))
+
 
 (unless (or (daemonp)
             init-file-debug)
@@ -85,7 +88,7 @@
     (when initdir
       ;; Discard the switch to prevent "invalid option" errors later.
       (add-to-list 'command-switch-alist (cons "--init-directory" (lambda (_) (pop argv))))
-      (setq user-emacs-directory initdir)))
+      (setq user-emacs-directory (expand-file-name initdir))))
 
   (let ((profile (or (cadr (member "--profile" command-line-args))
                      (getenv-internal "DOOMPROFILE"))))
@@ -136,7 +139,9 @@
   ;; Load the heart of Doom Emacs
   (if (require 'doom (expand-file-name "lisp/doom" user-emacs-directory) t)
       ;; ...and prepare for an interactive session.
-      (setq init-file (expand-file-name "doom-start" doom-core-dir))
+      (if noninteractive
+          (require 'doom-cli)
+        (setq init-file (expand-file-name "doom-start" doom-core-dir)))
     ;; ...but if that fails, then this is likely not a Doom config.
     (setq early-init-file (expand-file-name "early-init" user-emacs-directory))
     (load early-init-file t (not init-file-debug)))