* mu4e: add mu4e-change-filenames-when-moving customization

mu4e/mu4e-proc.el

@@ -376,6 +376,11 @@ The flags are any of `deleted', `flagged', `new', `passed', `replied' `seen' or
 `mu4e-string-to-flags' and `mu4e-flags-to-string'.
 The server reports the results for the operation through
 `mu4e-update-func'.
+
+If the the variable `mu4e-change-filenames-when-moving' is non-nil,
+the move generates new names for the target files; this helps
+certain tools (such as mbsync).
+
 The results are reported through either (:update ... )
 or (:error ) sexp, which are handled my `mu4e-update-func' and
 `mu4e-error-func', respectively."
@@ -391,8 +396,9 @@ or (:error ) sexp, which are handled my `mu4e-update-func' and
 	  (path
 	    (when maildir
 	      (format " maildir:%s" (mu4e~proc-escape maildir)))))
-    (mu4e~proc-send-command "cmd:move %s %s %s"
-      idparam (or flagstr "") (or path ""))))
+    (mu4e~proc-send-command "cmd:move %s %s %s %s"
+      idparam (or flagstr "") (or path "")
+      (format "newname:%s" (if mu4e-change-filenames-when-moving "true" "false")))))
 
 (defun mu4e~proc-index (path my-addresses)
   "Update the message database for filesystem PATH, which should

mu4e/mu4e-vars.el

@@ -71,6 +71,19 @@ mu4e."
   :group 'mu4e
   :safe 'integerp)
 
+
+(defcustom mu4e-change-filenames-when-moving nil
+  "When moving messages to different folders, normally mu/mu4e keep
+the the base filename the same (the flags-part of the filename may
+change still). With this option set to non-nil, mu4e instead
+changes the filename. This latter behavior works better with some
+IMAP-synchronization programs such as mbsync; the default works
+better with e.g. offlineimap."
+  :type 'boolean
+  :group 'mu4e
+  :safe 'booleanp)
+
+
 (defcustom mu4e-attachment-dir (expand-file-name "~/")
   "Default directory for saving attachments.
 This can be either a string, or a function that takes a filename
@@ -215,6 +228,7 @@ the From: address.)"
   :type 'string
   :group 'mu4e-compose)
 
+
 ;; backward compatibility
 (make-obsolete-variable 'mu4e-reply-to-address 'mu4e-compose-reply-to-address
   "v0.9.9")

mu4e/mu4e.texi

@@ -2913,6 +2913,11 @@ number of places.
 @item @emph{Can I start @t{mu4e} in the background?} Yes - if you provide a
 prefix-argument (@key{C-u}), @t{mu4e} starts, but does not show the
 main-window.
+@item @emph{Some IMAP-synchronization programs such as @t{mbsync} (but not
+@t{offlineimap}) don't like it when message files do not change their names
+when they are moved to different folders. Can @t{mu4e} somehow accomodate
+this?} Yes - you can set the variable @code{mu4e-change-filenames-when-moving}
+to non-nil.
 @end enumerate
 
 @node Reading messages