[PATCH v3] emacs: show: improve handling of mark read tagging errors

[Mark Walters]

Previously if a marking read tag change (i.e., removing the unread
tag) failed for some reason, such as a locked database, then no more
mark read tag changes would be attempted in that buffer.

This handles the error more gracefully. There is not much we can do
yet about dealing with the error itself, and marking read is probably
not important enough to warrant keeping a queue of pending changes or
anything.

However this commit changes it so that

- we do try and make future mark read tag changes.

- we display the tag state correctly: i.e. we don't display the tag as
  deleted (no strike through)

- and since we know the tag change failed we can try to mark this
  message read in the future. Indeed, since the code uses the
  post-command hook we will try again on the next keypress (unless the
  user has left the message).

We indicate to the user that these mark read tag changes may have
failed in the header-line and by a message in the echo area.
---

Hi

The best level of user notification in case of an error is
unclear. The best we came up with on irc is this one:

On first error, the headerline is changed to say (in warning face)
that some mark read tag changes may have failed.

On each error, which will occur on each call to
notmuch-show-command-hook (so roughly after each keypress) we write
the error to the error buffer and we send a message to the echo area.

In principle I would like to send a single message to the echo area
and have it persist for a few seconds. However, the echo area is
cleared after each keypress so this seems difficult. Moreover, this
clearing means if we send the message a single time and the user
enters the message with repeated cursor-downs then the message will
disappear as soon as it is displayed.

In the future we might want to modify the error code to be something like the
message buffer and say "last error repeated x times", but that can
come later.

Best wishes

Mark


 emacs/notmuch-show.el | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/emacs/notmuch-show.el b/emacs/notmuch-show.el
index fea39fa..406f418 100644
--- a/emacs/notmuch-show.el
+++ b/emacs/notmuch-show.el
@@ -1701,12 +1701,27 @@ user decision and we should not override it."
 	(notmuch-show-mark-read)
 	(notmuch-show-set-prop :seen t)))
 
+(defvar notmuch-show--seen-has-errored nil)
+(make-variable-buffer-local 'notmuch-show--seen-has-errored)
+
 (defun notmuch-show-command-hook ()
   (when (eq major-mode 'notmuch-show-mode)
     ;; We need to redisplay to get window-start and window-end correct.
     (redisplay)
     (save-excursion
-      (funcall notmuch-show-mark-read-function (window-start) (window-end)))))
+      (condition-case nil
+	  (funcall notmuch-show-mark-read-function (window-start) (window-end))
+	((debug error)
+	 ;; The call chain from notmuch-show-mark-read-function writes
+	 ;; and error to the error buffer before calling the error, so
+	 ;; we do not need to do that here. Just tell the user.
+	 (message "Warning -- marking message read failed.")
+	 (unless notmuch-show--seen-has-errored
+	   (setq notmuch-show--seen-has-errored 't)
+	   (setq header-line-format
+		 (concat header-line-format
+			 (propertize "  [some mark read tag changes may have failed]"
+				     'face font-lock-warning-face)))))))))
 
 (defun notmuch-show-filter-thread (query)
   "Filter or LIMIT the current thread based on a new query string.
-- 
2.1.4