lib: New function to collect tags from a list of messages.

This patch adds a new function that can be used to collect a list of
unique tags from a list of messages. 'notmuch search-tags' uses the
function to get a list of tags from messages matching a search-term,
but it has the potential to be used elsewhere so we put it in the lib.

Signed-off-by: Jan Janak <jan@ryngle.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/lib/notmuch.h b/lib/notmuch.h
index c05e802..9fa2770 100644
--- a/lib/notmuch.h
+++ b/lib/notmuch.h
@@ -635,6 +635,21 @@ notmuch_messages_advance (notmuch_messages_t *messages);
 void
 notmuch_messages_destroy (notmuch_messages_t *messages);
 
+/* Return a list of tags from all messages.
+ *
+ * The resulting list is guaranteed not to contain duplicated tags.
+ *
+ * WARNING: You can no longer iterate over messages after calling this
+ * function, because the iterator will point at the end of the list.
+ * We do not have a function to reset the iterator yet and the only
+ * way how you can iterate over the list again is to recreate the
+ * message list.
+ *
+ * The function returns NULL on error.
+ */
+notmuch_tags_t *
+notmuch_messages_collect_tags (notmuch_messages_t *messages);
+
 /* Get the message ID of 'message'.
  *
  * The returned string belongs to 'message' and as such, should not be