[nongnu] elpa/opam-switch-mode d3a7536570 2/4: refactor: Memoize (opam-switch-mode-lighter) to speed-up mode-line updates

[ELPA Syncer]

branch: elpa/opam-switch-mode
commit d3a75365702ae49eaad9324bbb90f0234a4df451
Author: Erik Martin-Dorel <erik@martin-dorel.org>
Commit: Erik Martin-Dorel <erik@martin-dorel.org>

    refactor: Memoize (opam-switch-mode-lighter) to speed-up mode-line updates
    
    Patch devised by @monnier (thanks!)
    
    Co-authored-by: Stefan Monnier <monnier@iro.umontreal.ca>
---
 NEWS.md             |  1 +
 opam-switch-mode.el | 15 +++++++++++----
 2 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/NEWS.md b/NEWS.md
index bbb0abbc54..f4a12c7265 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -15,6 +15,7 @@ The format is based on [Keep a 
Changelog](https://keepachangelog.com/en/1.0.0/).
 
 - **README.md**: Use vanilla (not GitHub-flavored) Markdown syntax for snippets
 - Replace (redraw-display) with (force-mode-line-update t)
+- Memoize (opam-switch-mode-lighter) to speed-up mode-line updates
 
 ### Removed
 
diff --git a/opam-switch-mode.el b/opam-switch-mode.el
index 065873e2ee..42ef7c41e9 100644
--- a/opam-switch-mode.el
+++ b/opam-switch-mode.el
@@ -93,6 +93,8 @@ background process before the opam switch changes."
 
 ;;; Code:
 
+(defvar opam-switch--mode-lighter nil)
+
 (defun opam-switch--run-command-without-stderr (sub-cmd
                                                 &optional switch sexp
                                                 &rest args)
@@ -321,6 +323,7 @@ not any other shells outside Emacs."
       (unless opam-switch--saved-env
         (opam-switch--save-current-env opam-env))
       (opam-switch--set-env opam-env prefix)))
+  (setq opam-switch--mode-lighter nil)
   (force-mode-line-update t)
   (run-hooks 'opam-switch-change-opam-switch-hook))
 
@@ -375,10 +378,14 @@ is automatically created by `define-minor-mode'."
 
 (defun opam-switch-mode-lighter ()
   "Return the lighter for opam-switch-mode which indicates the current switch."
-  (let* ((current-switch (opam-switch--get-current-switch))
-         ;; handle the case of local switches for better UX
-         (shortened (replace-regexp-in-string ".*/" "…/" current-switch t t)))
-    (format " OPSW-%s" shortened)))
+  (or opam-switch--mode-lighter
+      (let* ((current-switch (opam-switch--get-current-switch))
+             ;; handle the case of local switches for better UX
+             (shortened
+              (replace-regexp-in-string ".*/" "…/" current-switch
+                                        t t)))
+        (setq opam-switch--mode-lighter
+              (format " OPSW-%s" shortened)))))
 
 ;;;###autoload
 (define-minor-mode opam-switch-mode