fill-column-master: keep RHS mode-line on screen

Ref: seagle0128/doom-modeline#672

config.el

@@ -136,7 +136,7 @@
 
 (after! doom-modeline
   (setq doom-modeline-buffer-file-name-style 'truncate-except-project
-        dirvish-mode-line-height doom-modeline-height)
+        mode-line-right-align-edge 'right-fringe)
 
   ;; Only display encoding in modeline when it's not UTF-8
   (add-hook 'after-change-major-mode-hook #'dtm-doom-modeline-conditional-encoding-h))
@@ -340,6 +340,7 @@
 
 (after! dirvish
   (setq dirvish-reuse-session nil
+        dirvish-mode-line-height doom-modeline-height
         dirvish-quick-access-entries
         `(("D" "~/Downloads/" "Downloads")
           ("dc" ,doom-core-dir "Doom Core")

modules/ui/zen-light/autoload/fill-column-master.el

@@ -6,22 +6,27 @@
   :init-value nil :lighter nil :global nil
   :after-hook (fill-column-master-adjust)
   (when (not fill-column-visual-mode)
-    (fill-column-master-manage-hooks fill-column-center-mode)))
+    (fill-column-master--manage-state fill-column-center-mode)))
 
 ;;;###autoload
 (define-minor-mode fill-column-visual-mode
   "Adjust right margin to end the buffer at `fill-column' in the current window."
   :init-value nil :lighter nil :global nil
   :after-hook (fill-column-master-adjust)
   (when (not fill-column-center-mode)
-    (fill-column-master-manage-hooks fill-column-visual-mode)))
+    (fill-column-master--manage-state fill-column-visual-mode)))
 
-(defun fill-column-master-manage-hooks (enable)
+(defun fill-column-master--manage-state (enable)
+  "Setup/teardown necessary hooks & variables depending on ENABLE.
+Ref: https://github.com/seagle0128/doom-modeline/issues/672"
   (if enable
       (progn
+        (when (eq mode-line-right-align-edge 'window)
+          (setq-local mode-line-right-align-edge 'right-margin))
         (add-hook 'window-configuration-change-hook #'fill-column-master-adjust 'append 'local)
         (add-hook 'display-line-numbers-mode-hook #'fill-column-master-adjust 'append 'local)
         (add-hook 'text-scale-mode-hook #'fill-column-master-adjust 'append 'local))
+    (kill-local-variable 'mode-line-right-align-edge)
     (remove-hook 'window-configuration-change-hook #'fill-column-master-adjust 'local)
     (remove-hook 'display-line-numbers-mode-hook #'fill-column-master-adjust 'local)
     (remove-hook 'text-scale-mode-hook #'fill-column-master-adjust 'local)))