mu4e-modeline: only cache global items, improve layout

So buffer-local items get flushed out automatically when we leave the
buffers where the local items were specified.

Honor mu4e-modeline-max-width

mu4e/mu4e-helpers.el

@@ -42,12 +42,6 @@
   :type 'boolean
   :group 'mu4e)
 
-(defcustom mu4e-modeline-max-width 42
-  "Determines the maximum length of the modeline string.
-If the string exceeds this limit, it will be truncated to fit."
-  :type 'integer
-  :group 'mu4e)
-
 (defcustom mu4e-completing-read-function 'ido-completing-read
   "Function to be used to receive user-input during completion.
 Suggested possible values are:
@@ -100,18 +94,7 @@ marked as read-only, or non-nil otherwise."
 
 
 
-;;; Modeline
 
-(defun mu4e-quote-for-modeline (str)
-  "Quote STR to be used literally in the modeline.
-The string will be shortened to fit if its length exceeds
-`mu4e-modeline-max-width'."
-  (replace-regexp-in-string
-   "%" "%%"
-   (truncate-string-to-width str mu4e-modeline-max-width 0 nil t)))
-
-
-
 ;;; Messages, warnings and errors
 (defun mu4e-format (frm &rest args)
   "Create [mu4e]-prefixed string based on format FRM and ARGS."

mu4e/mu4e-modeline.el

@@ -29,6 +29,17 @@
 
 (require 'cl-lib)
 
+
+(defcustom mu4e-modeline-max-width 42
+  "Determines the maximum length of the local modeline string.
+If the string exceeds this limit, it will be truncated to fit.
+
+Note: this only affects the local modeline items (such as the context,
+the search properties and the last query), not the global items
+(such as the favorite bookmark results)."
+  :type 'integer
+  :group 'mu4e-modeline)
+
 (defvar-local mu4e--modeline-buffer-items nil
   "List of buffer-local items for the mu4e modeline.
 Each element is function that evaluates to a string.")
@@ -45,23 +56,42 @@ the buffer-local one."
    (if global
        'mu4e--modeline-global-items
      'mu4e--modeline-buffer-items)
-   func))
+   func 'append))
+
+(defun mu4e--modeline-quote-and-truncate (str)
+  "Quote STR to be used literally in the modeline.
+The string is truncaed to fit if its length exceeds
+`mu4e-modeline-max-width'."
+  (replace-regexp-in-string
+   "%" "%%"
+   (truncate-string-to-width str mu4e-modeline-max-width 0 nil t)))
 
 (defvar mu4e--modeline-item nil
   "Mu4e item for the global-mode-line.")
 
-(defvar mu4e--modeline-string-cached nil
-  "Cached version of the modeline string.")
+(defvar mu4e--modeline-global-string-cached nil
+  "Cached version of the _global_ modeline string.
+Note that we don't cache the local parts, so that the modeline
+gets updated when we leave the buffer from which the local parts
+originate.")
 
 (defun mu4e--modeline-string ()
   "Get the current mu4e modeline string."
-  (or mu4e--modeline-string-cached
-      (setq mu4e--modeline-string-cached
+  (let* ((collect
+          (lambda (lst)
             (mapconcat
-             (lambda (func) (or (funcall func) ""))
-             (append mu4e--modeline-buffer-items
-                     mu4e--modeline-global-items)
-             " "))))
+             (lambda (func) (or (funcall func) "")) lst " ")))
+         (global-string ;; global string is _cached_ as it may be expensive.
+          (or mu4e--modeline-global-string-cached
+              (setq mu4e--modeline-global-string-cached
+                    (funcall collect mu4e--modeline-global-items)))))
+    (concat
+     ;; (local) buffer items are _not_ cached, so they'll get update
+     ;; automatically when leaving the buffer.
+     (mu4e--modeline-quote-and-truncate
+      (funcall collect mu4e--modeline-buffer-items))
+     " "
+     global-string)))
 
 (define-minor-mode mu4e-modeline-mode
   "Minor mode for showing mu4e information on the modeline."
@@ -85,7 +115,7 @@ the buffer-local one."
 (defun mu4e--modeline-update ()
   "Recalculate and force-update the modeline."
   (when mu4e-modeline-mode
-    (setq mu4e--modeline-string-cached nil)
+    (setq mu4e--modeline-global-string-cached nil)
     (force-mode-line-update)))
 
 (provide 'mu4e-modeline)