lib: Remove unnecessary thread linking steps when using ghost messages

Previously, it was necessary to link new messages to children to work
around some (though not all) problems with the old metadata-based
approach to stored thread IDs.  With ghost messages, this is no longer
necessary, so don't bother with child linking when ghost messages are
in use.

diff --git a/lib/database.cc b/lib/database.cc
index b673718223aa448bf22e7fb01101e20daa8eac7a..3601f9ded30778620e18a5835de00e6e00ef7854 100644 (file)
--- a/lib/database.cc
+++ b/lib/database.cc
@@ -2136,11 +2136,11 @@ _consume_metadata_thread_id (void *ctx, notmuch_database_t *notmuch,
  * reference 'message'.
  *
  * In all cases, we assign to the current message the first thread ID
- * found (through either parent or child). We will also merge any
- * existing, distinct threads where this message belongs to both,
- * (which is not uncommon when messages are processed out of order).
+ * found. We will also merge any existing, distinct threads where this
+ * message belongs to both, (which is not uncommon when messages are
+ * processed out of order).
  *
- * Finally, if no thread ID has been found through parent or child, we
+ * Finally, if no thread ID has been found through referenced messages, we
  * call _notmuch_message_generate_thread_id to generate a new thread
  * ID. This should only happen for new, top-level messages, (no
  * References or In-Reply-To header in this message, and no previously
@@ -2172,10 +2172,23 @@ _notmuch_database_link_message (notmuch_database_t *notmuch,
     if (status)
        goto DONE;
 
-    status = _notmuch_database_link_message_to_children (notmuch, message,
-                                                        &thread_id);
-    if (status)
-       goto DONE;
+    if (! (notmuch->features & NOTMUCH_FEATURE_GHOSTS)) {
+       /* In general, it shouldn't be necessary to link children,
+        * since the earlier indexing of those children will have
+        * stored a thread ID for the missing parent.  However, prior
+        * to ghost messages, these stored thread IDs were NOT
+        * rewritten during thread merging (and there was no
+        * performant way to do so), so if indexed children were
+        * pulled into a different thread ID by a merge, it was
+        * necessary to pull them *back* into the stored thread ID of
+        * the parent.  With ghost messages, we just rewrite the
+        * stored thread IDs during merging, so this workaround isn't
+        * necessary. */
+       status = _notmuch_database_link_message_to_children (notmuch, message,
+                                                            &thread_id);
+       if (status)
+           goto DONE;
+    }
 
     /* If not part of any existing thread, generate a new thread ID. */
     if (thread_id == NULL) {