From 848cc117c4555c424fcd7f16d363b5da8118f36d Mon Sep 17 00:00:00 2001
From: Henrik Lissner <henrik@lissner.net>
Date: Wed, 26 Aug 2020 17:23:31 -0400
Subject: [PATCH] ui/modeline: cache buffer id for +light modeline

---
 modules/ui/modeline/+light.el | 45 +++++++++++++++++++++++++----------
 1 file changed, 33 insertions(+), 12 deletions(-)

diff --git a/modules/ui/modeline/+light.el b/modules/ui/modeline/+light.el
index 6d1eab924..0eab73319 100644
--- a/modules/ui/modeline/+light.el
+++ b/modules/ui/modeline/+light.el
@@ -353,20 +353,41 @@ Requires `anzu', also `evil-anzu' if using `evil-mode' for compatibility with
 
 
 ;;; `+modeline-buffer-identification'
+(defvar-local +modeline--buffer-id-cache nil)
+
+(add-transient-hook! 'doom-first-buffer-hook
+  ;; REVIEW Generating the buffer's file name can be relatively expensive.
+  ;;        Compounded with how often the modeline updates this can add up, so
+  ;;        we cache it ahead of time.
+  (add-hook! '(change-major-mode-after-body-hook
+               ;; In case the user saves the file to a new location
+               after-save-hook
+               ;; ...or makes external changes then returns to Emacs
+               focus-in-hook
+               ;; ...or when we change the current project!
+               projectile-after-switch-project-hook
+               ;; ...when the underlying file changes
+               after-revert-hook)
+    (defun +modeline--generate-buffer-id-cache-h ()
+      (setq +modeline--buffer-id-cache
+            (let ((file-name (buffer-file-name (buffer-base-buffer))))
+              (unless (or (null default-directory)
+                          (null file-name)
+                          (file-remote-p file-name))
+                (when-let ((project-root (doom-project-root)))
+                  (file-relative-name
+                   (or buffer-file-truename (file-truename file-name))
+                   (concat project-root "..")))))))))
+
 (def-modeline-var! +modeline-buffer-identification ; slightly more informative buffer id
   '((:eval
-     (let ((file-name (buffer-file-name (buffer-base-buffer))))
-       (propertize
-        (or (when (and file-name (not (file-remote-p file-name)))
-              (when-let (project (doom-project-root file-name))
-                (file-relative-name (or buffer-file-truename (file-truename file-name))
-                                    (concat project ".."))))
-            "%b")
-        'face (cond ((buffer-modified-p)
-                     '(error bold mode-line-buffer-id))
-                    ((+modeline-active)
-                     'mode-line-buffer-id))
-        'help-echo file-name)))
+     (propertize
+      (or +modeline--buffer-id-cache "%b")
+      'face (cond ((buffer-modified-p)
+                   '(error bold mode-line-buffer-id))
+                  ((+modeline-active)
+                   'mode-line-buffer-id))
+      'help-echo (or +modeline--buffer-id-cache (buffer-name))))
     (buffer-read-only (:propertize " RO" face warning))))