perf(rendering): cache results of whale-line--format-side

CHANGELOG.md

@@ -11,6 +11,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Keyword `:wraps` for augments. This is a shorthand to `:after-while`
   and passing the name of the render function of another segment.
+- Results `whale-line--format-side` are now cached until window
+  configuration changes.
 
 ## [0.8.3]
 

test/whale-line-test.el

@@ -982,6 +982,18 @@
 
   (should-error (whale-line--symbol-for-type 'segment 'something)))
 
+(ert-deftest whale-line--format-side--uses-cache ()
+  (let ((whale-line--render-cache (make-hash-table :test 'equal)))
+
+    (bydi ((:mock whale-line--render :return "hello")
+           (:mock format-mode-line :with bydi-rf))
+
+      (whale-line--format-side :left)
+
+      (should (equal (nth 0 (hash-table-keys whale-line--render-cache)) '(:left nil)))
+
+      (should (string= "hello" (whale-line--format-side :left))))))
+
 ;;; whale-line-test.el ends here
 
 ;; Local Variables:

whale-line.el

@@ -93,6 +93,7 @@ logging."
 
 (defvar whale-line--padded-cache (make-hash-table))
 (defvar whale-line--space-cache (make-hash-table))
+(defvar whale-line--render-cache (make-hash-table :test 'equal))
 
 (defvar whale-line--stateful-timer nil)
 
@@ -189,7 +190,11 @@ formatter to call."
   "Get the formatted SIDE.
 
 Optionally FILTER out low priority segments."
-  (format-mode-line (whale-line--render side filter)))
+  (if-let* ((value (gethash (list side filter) whale-line--render-cache)))
+      value
+    (let ((render (format-mode-line (whale-line--render side filter))))
+
+      (puthash (list side filter) render whale-line--render-cache))))
 
 ;;;; Space calculation
 
@@ -270,7 +275,8 @@ This uses `string-pixel-width' for Emacs 29+, otherwise
 (defun whale-line--clear-caches ()
   "Clear all caches."
   (clrhash whale-line--padded-cache)
-  (clrhash whale-line--space-cache))
+  (clrhash whale-line--space-cache)
+  (clrhash whale-line--render-cache))
 
 ;;;; Building segments