mu4e: integrate mkdir better into mu4e

When moving to a non-existent folder, offer to create it and proceed from
there (that _almost_ worked earlier).

Fixes #628
Fixes #477

mu4e/mu4e-folders.el

@@ -195,7 +195,6 @@ See `mu4e-sent-folder'." (mu4e--get-folder 'mu4e-sent-folder msg))
   "Get the trash folder, optionallly based on MSG.
 See `mu4e-trash-folder'." (mu4e--get-folder 'mu4e-trash-folder msg))
 
-
 ;;; Maildirs
 (defun mu4e--guess-maildir (path)
   "Guess the maildir for PATH, or nil if cannot find it."
@@ -209,17 +208,15 @@ See `mu4e-trash-folder'." (mu4e--get-folder 'mu4e-trash-folder msg))
 
 (defun mu4e-create-maildir-maybe (dir)
   "Offer to create maildir DIR if it does not exist yet.
-Return t if the dir already existed, or an attempt has been made to
-create it -- we cannot be sure creation succeeded here, since this
-is done asynchronously. Otherwise, return nil. NOte, DIR has to be
-an absolute path."
-  (if (and (file-exists-p dir) (not (file-directory-p dir)))
-      (mu4e-error "File %s exists, but is not a directory" dir)
-    (cond
-     ((file-directory-p dir) t)
-     ((yes-or-no-p (mu4e-format "%s does not exist yet. Create now?" dir))
-      (mu4e--server-mkdir dir) t)
-     (t nil))))
+Return t if it already exists or (after asking) an attempt has been
+to create it; otherwise return nil."
+  (let ((seems-to-exist (file-directory-p dir)))
+    (when (or seems-to-exist
+              (yes-or-no-p (mu4e-format "%s does not exist yet. Create now?" dir)))
+      ;; even when the maildir already seems to exist,
+      ;; call mkdir for a deeper check. However only get an update
+      ;; when the maildir is totally new.
+      (mu4e--server-mkdir dir (not seems-to-exist)) t)))
 
 (defun mu4e~get-maildirs-1 (path mdir)
   "Get maildirs for MDIR under PATH.

mu4e/mu4e-mark.el

@@ -280,17 +280,12 @@ The following marks are available, and the corresponding props:
 
 (defun mu4e--mark-get-move-target ()
   "Ask for a move target, and propose to create it if it does not exist."
-  (interactive)
-  ;;  (mu4e-message-at-point) ;; raises error if there is none
   (let* ((target (mu4e-ask-maildir "Move message to: "))
          (target (if (string= (substring target 0 1) "/")
                      target
                    (concat "/" target)))
          (fulltarget (mu4e-join-paths (mu4e-root-maildir) target)))
-    (when (or (file-directory-p fulltarget)
-              (and (yes-or-no-p
-                    (format "%s does not exist.  Create now?" fulltarget))
-                   (mu4e--server-mkdir fulltarget)))
+    (when (mu4e-create-maildir-maybe fulltarget)
       target)))
 
 (defun mu4e--mark-ask-target (mark)

mu4e/mu4e-server.el

@@ -557,9 +557,12 @@ the directory time stamp."
    `(index :cleanup ,(and cleanup t)
            :lazy-check ,(and lazy-check t))))
 
-(defun mu4e--server-mkdir (path)
-  "Create a new maildir-directory at filesystem PATH."
-  (mu4e--server-call-mu `(mkdir :path ,path)))
+(defun mu4e--server-mkdir (path &optional update)
+  "Create a new maildir-directory at filesystem PATH.
+When UPDATE is non-nil, send a update when completed."
+  (mu4e--server-call-mu `(mkdir
+                          :path ,path
+                          :update ,(or update nil))))
 
 (defun mu4e--server-move (docid-or-msgid &optional maildir flags no-view)
   "Move message identified by DOCID-OR-MSGID.