feat: backport align-right feature from 30.

Closes #646.

doom-modeline-core.el

@@ -33,6 +33,79 @@
 (require 'nerd-icons)
 (require 'shrink-path)
 
+
+;;
+;; Compatibility
+;;
+
+;; Backport from 30
+(unless (fboundp 'mode--line-format-right-align)
+  (defcustom mode-line-right-align-edge 'window
+    "Where function `mode-line-format-right-align' should align to.
+Internally, that function uses `:align-to' in a display property,
+so aligns to the left edge of the given area.  See info node
+`(elisp)Pixel Specification'.
+
+Must be set to a symbol.  Acceptable values are:
+- `window': align to extreme right of window, regardless of margins
+  or fringes
+- `right-fringe': align to right-fringe
+- `right-margin': align to right-margin"
+    :type '(choice (const right-margin)
+                   (const right-fringe)
+                   (const window))
+    :group 'mode-line)
+
+  (defun mode--line-format-right-align ()
+    "Right-align all following mode-line constructs.
+
+When the symbol `mode-line-format-right-align' appears in
+`mode-line-format', return a string of one space, with a display
+property to make it appear long enough to align anything after
+that symbol to the right of the rendered mode line.  Exactly how
+far to the right is controlled by `mode-line-right-align-edge'.
+
+It is important that the symbol `mode-line-format-right-align' be
+included in `mode-line-format' (and not another similar construct
+such as `(:eval (mode-line-format-right-align)').  This is because
+the symbol `mode-line-format-right-align' is processed by
+`format-mode-line' as a variable."
+    (let* ((rest (cdr (memq 'mode-line-format-right-align
+			                mode-line-format)))
+	       (rest-str (format-mode-line `("" ,@rest)))
+	       (rest-width (progn
+                         (add-face-text-property
+                          0 (length rest-str) 'mode-line t rest-str)
+                         (string-pixel-width rest-str))))
+      (propertize " " 'display
+		          ;; The `right' spec doesn't work on TTY frames
+		          ;; when windows are split horizontally (bug#59620)
+		          (if (and (display-graphic-p)
+                           (not (eq mode-line-right-align-edge 'window)))
+		              `(space :align-to (- ,mode-line-right-align-edge
+                                           (,rest-width)))
+		            `(space :align-to (,(- (window-pixel-width)
+                                           (window-scroll-bar-width)
+                                           (window-right-divider-width)
+                                           (* (or (cdr (window-margins)) 1)
+                                              (frame-char-width))
+                                           ;; Manually account for value of
+                                           ;; `mode-line-right-align-edge' even
+                                           ;; when display is non-graphical
+                                           (pcase mode-line-right-align-edge
+                                             ('right-margin
+                                              (or (cdr (window-margins)) 0))
+                                             ('right-fringe
+                                              ;; what here?
+                                              (or (cadr (window-fringes)) 0))
+                                             (_ 0))
+                                           rest-width)))))))
+
+  (defvar mode-line-format-right-align '(:eval (mode--line-format-right-align))
+    "Mode line construct to right align all following constructs.")
+  ;;;###autoload
+  (put 'mode-line-format-right-align 'risky-local-variable t))
+
 
 ;;
 ;; Optimization
@@ -1078,24 +1151,7 @@ Example:
         (rhs-forms (doom-modeline--prepare-segments rhs)))
     (defalias sym
       (lambda ()
-        (list lhs-forms
-              (propertize
-               " "
-               'face (doom-modeline-face)
-               'display `(space
-                          :align-to
-                          (- (+ right right-fringe right-margin scroll-bar)
-                             ,(let ((rhs-str (format-mode-line (cons "" rhs-forms))))
-                                (if (and (>= emacs-major-version 29)
-                                         (fboundp 'string-pixel-width))
-                                    (/ (string-pixel-width rhs-str)
-                                       (doom-modeline--font-width)
-                                       1.0)
-                                  (* (string-width rhs-str)
-                                     (if (display-graphic-p)
-                                         (/ (doom-modeline--font-width) (frame-char-width) 0.95)
-                                       1.0)))))))
-              rhs-forms))
+        `(,lhs-forms ,rhs-forms))
       (concat "Modeline:\n"
               (format "  %s\n  %s"
                       (prin1-to-string lhs)
@@ -1107,7 +1163,10 @@ Example:
 Throws an error if it doesn't exist."
   (let ((fn (intern-soft (format "doom-modeline-format--%s" key))))
     (when (functionp fn)
-      `(:eval (,fn)))))
+      (let* ((modeline (funcall fn))
+             (lhs (car modeline))
+             (rhs (cdr modeline)))
+        `(,lhs mode-line-format-right-align ,rhs)))))
 
 (defun doom-modeline-set-modeline (key &optional default)
   "Set the modeline format. Does nothing if the modeline KEY doesn't exist.
@@ -1116,7 +1175,7 @@ If DEFAULT is non-nil, set the default mode-line for all buffers."
     (setf (if default
               (default-value 'mode-line-format)
             mode-line-format)
-          (list "%e" modeline))))
+          modeline)))
 
 
 ;;