New incremental lazy-loading at startup

This is for loading large packages (like org and magit) quietly in the
background during idle time. It is already set up to incrementally load
org and magit.

This is still experimental, however. the idle timers may need to be
tweaked.

core/core.el

@@ -300,6 +300,69 @@ original value of `symbol-file'."
 (add-hook 'minibuffer-exit-hook  #'doom|restore-garbage-collection)
 
 
+;;
+;; Incremental lazy-loading
+
+(defvar doom-incremental-packages '(t)
+  "A list of packages to load incrementally after startup. Any large packages
+here may cause noticable pauses, so it's recommended you break them up into
+sub-packages. For example, `org' is comprised of many packages, and can be broken up into:
+
+  (doom-load-packages-incrementally
+   '(calendar find-func format-spec org-macs org-compat
+     org-faces org-entities org-list org-pcomplete org-src
+     org-footnote org-macro ob org org-clock org-agenda
+     org-capture))
+
+This is already done by the lang/org module, however.
+
+If you want to disable incremental loading altogether, either remove
+`doom|load-packages-incrementally' from `emacs-startup-hook' or set
+`doom-incremental-first-idle-timer' to nil.")
+
+(defvar doom-incremental-first-idle-timer 2
+  "How long (in idle seconds) until incremental loading starts.
+
+Set this to nil to disable incremental loading.")
+
+(defvar doom-incremental-idle-timer 1.5
+  "How long (in idle seconds) in between incrementally loading packages.")
+
+(defun doom-load-packages-incrementally (packages &optional now)
+  "Registers PACKAGES to be loaded incrementally.
+
+If NOW is non-nil, load PACKAGES incrementally, in `doom-incremental-idle-timer'
+intervals."
+  (if (not now)
+      (nconc doom-incremental-packages packages)
+    (when packages
+      (let ((gc-cons-threshold doom-gc-cons-upper-limit)
+            file-name-handler-alist)
+        (let* ((reqs (cl-remove-if #'featurep packages))
+               (req (ignore-errors (pop reqs))))
+          (when req
+            (when doom-debug-mode
+              (message "Incrementally loading %s" req))
+            (require req)
+            (when reqs
+              (run-with-idle-timer doom-incremental-idle-timer
+                                   nil #'doom-load-packages-incrementally
+                                   reqs t))))))))
+
+(defun doom|load-packages-incrementally ()
+  "Begin incrementally loading packages in `doom-incremental-packages'.
+
+If this is a daemon session, load them all immediately instead."
+  (if (daemonp)
+      (mapc #'require (cdr doom-incremental-packages))
+    (when (integerp doom-incremental-first-idle-timer)
+      (run-with-idle-timer doom-incremental-first-idle-timer
+                           nil #'doom-load-packages-incrementally
+                           (cdr doom-incremental-packages) t))))
+
+(add-hook 'emacs-startup-hook #'doom|load-packages-incrementally)
+
+
 ;;
 ;; Bootstrap helpers
 

modules/lang/org/config.el

@@ -13,6 +13,12 @@
 (if (featurep! +present) (load! "+present"))
 ;; TODO (if (featurep! +publish) (load! "+publish"))
 
+(doom-load-packages-incrementally
+ '(calendar find-func format-spec org-macs org-compat
+   org-faces org-entities org-list org-pcomplete org-src
+   org-footnote org-macro ob org org-clock org-agenda
+   org-capture))
+
 
 ;;
 ;; Packages

modules/tools/magit/config.el

@@ -18,6 +18,8 @@ available.")
   :commands magit-file-delete
   :init
   (setq magit-auto-revert-mode nil)  ; we already use `global-auto-revert-mode'
+  (doom-load-packages-incrementally
+   '(dash f s with-editor git-commit package magit))
   :config
   (setq magit-completing-read-function
         (if (featurep! :completion ivy)