Resize headers window after displaying a message

mu4e/mu4e-view.el

@@ -112,6 +112,10 @@ specified a function as viewer."
   :type 'integer
   :group 'mu4e-view)
 
+(defcustom mu4e-after-view-message-hook '(mu4e-resize-linked-headers-window)
+  "Hook run by `mu4e-view' after a message is rendered."
+  :type 'hook
+  :group 'mu4e-view)
 
 
 
@@ -644,7 +648,9 @@ As a side-effect, a message that is being viewed loses its
       (setq-local mu4e~headers-view-win (mu4e-display-buffer gnus-article-buffer nil))
       (unless (window-live-p mu4e~headers-view-win)
         (mu4e-error "Cannot get a message view"))
-      (select-window mu4e~headers-view-win))))
+      (select-window mu4e~headers-view-win)))
+  (with-current-buffer gnus-article-buffer
+    (run-hooks 'mu4e-after-view-message-hook)))
 
 (defun mu4e-view-message-text (msg)
   "Return the pristine MSG as a string."

mu4e/mu4e-window.el

@@ -242,5 +242,30 @@ for BUFFER-OR-NAME to be displayed in."
                buffer-name
                arg))))
 
+(defun mu4e-resize-linked-headers-window ()
+  "Resizes the linked headers window belonging to a view.
+
+Resizes the current headers view according to `mu4e-split-view'
+and `mu4e-headers-visible-lines' or
+`mu4e-headers-visible-columns'.
+
+This function is best called from the hook
+`mu4e-after-view-message-hook'."
+  (unless (mu4e-current-buffer-type-p 'view)
+    (error "Cannot resize as this is not a valid view buffer."))
+  (when-let (win (and mu4e-linked-headers-buffer
+                      (get-buffer-window mu4e-linked-headers-buffer)))
+    ;; This can fail for any number of reasons. If it does, we do
+    ;; nothing. If the user has customized the window display we may
+    ;; find it impossible to resize the window, and that should not be
+    ;; cause for error.
+    (ignore-errors
+      (cond ((eq mu4e-split-view 'vertical)
+             (window-resize win (- mu4e-headers-visible-columns (window-width win nil))
+                            t t nil))
+            ((eq mu4e-split-view 'horizontal)
+             (set-window-text-height win mu4e-headers-visible-lines))))))
+
+
 (provide 'mu4e-window)
 ;;; mu4e-window.el ends here