tag-util: optimization of tag application

The idea is not to bother with restore operations if they don't change
the set of tags. This is actually a relatively common case.

In order to avoid fancy datastructures, this method is quadratic in
the number of tags; at least on my mail database this doesn't seem to
be a big problem.

diff --git a/tag-util.c b/tag-util.c
index 6d33ef8f3010be5ebf7fe932c23a5db4b9245d09..eab482f3012888b6c401b85b3775b01c274d7d5f 100644 (file)
--- a/tag-util.c
+++ b/tag-util.c
@@ -151,6 +151,71 @@ message_error (notmuch_message_t *message,
     fprintf (stderr, "Status: %s\n", notmuch_status_to_string (status));
 }
 
+static int
+makes_changes (notmuch_message_t *message,
+              tag_op_list_t *list,
+              tag_op_flag_t flags)
+{
+
+    size_t i;
+
+    notmuch_tags_t *tags;
+    notmuch_bool_t changes = FALSE;
+
+    /* First, do we delete an existing tag? */
+    changes = FALSE;
+    for (tags = notmuch_message_get_tags (message);
+        ! changes && notmuch_tags_valid (tags);
+        notmuch_tags_move_to_next (tags)) {
+       const char *cur_tag = notmuch_tags_get (tags);
+       int last_op =  (flags & TAG_FLAG_REMOVE_ALL) ? -1 : 0;
+
+       /* scan backwards to get last operation */
+       i = list->count;
+       while (i > 0) {
+           i--;
+           if (strcmp (cur_tag, list->ops[i].tag) == 0) {
+               last_op = list->ops[i].remove ? -1 : 1;
+               break;
+           }
+       }
+
+       changes = (last_op == -1);
+    }
+    notmuch_tags_destroy (tags);
+
+    if (changes)
+       return TRUE;
+
+    /* Now check for adding new tags */
+    for (i = 0; i < list->count; i++) {
+       notmuch_bool_t exists = FALSE;
+
+       if (list->ops[i].remove)
+           continue;
+
+       for (tags = notmuch_message_get_tags (message);
+            notmuch_tags_valid (tags);
+            notmuch_tags_move_to_next (tags)) {
+           const char *cur_tag = notmuch_tags_get (tags);
+           if (strcmp (cur_tag, list->ops[i].tag) == 0) {
+               exists = TRUE;
+               break;
+           }
+       }
+       notmuch_tags_destroy (tags);
+
+       /* the following test is conservative,
+        * in the sense it ignores cases like +foo ... -foo
+        * but this is OK from a correctness point of view
+        */
+       if (! exists)
+           return TRUE;
+    }
+    return FALSE;
+
+}
+
 notmuch_status_t
 tag_op_list_apply (notmuch_message_t *message,
                   tag_op_list_t *list,
@@ -160,6 +225,9 @@ tag_op_list_apply (notmuch_message_t *message,
     notmuch_status_t status = 0;
     tag_operation_t *tag_ops = list->ops;
 
+    if (! (flags & TAG_FLAG_PRE_OPTIMIZED) && ! makes_changes (message, list, flags))
+       return NOTMUCH_STATUS_SUCCESS;
+
     status = notmuch_message_freeze (message);
     if (status) {
        message_error (message, status, "freezing message");