[PATCH 2/2] fix thread breakage via ghost-on-removal

[Daniel Kahn Gillmor]

This is the solution to T590-thread-breakage.sh that just adds a ghost
message after removing each message.

It leaks information about whether we've ever seen a given message id,
but it's a fairly simple implementation.

Note that _resolve_message_id_to_thread_id also introduces new
message_ids to the database, so i think just searching for a given
message ID may introduce the same metadata leakage.
---
 lib/database.cc | 28 ++++++++++++++++++++++++++--
 1 file changed, 26 insertions(+), 2 deletions(-)

diff --git a/lib/database.cc b/lib/database.cc
index 3b342f1..6c9e34a 100644
--- a/lib/database.cc
+++ b/lib/database.cc
@@ -2557,9 +2557,33 @@ notmuch_database_remove_message (notmuch_database_t *notmuch,
 
     if (status == NOTMUCH_STATUS_SUCCESS && message) {
 	    status = _notmuch_message_remove_filename (message, filename);
-	    if (status == NOTMUCH_STATUS_SUCCESS)
+	    if (status == NOTMUCH_STATUS_SUCCESS) {
+		const char *mid, *tid;
+		notmuch_message_t *ghost;
+		notmuch_private_status_t private_status;
+	    
+		mid = notmuch_message_get_message_id (message);
+		tid = notmuch_message_get_thread_id (message);
+		/* remove the message */
 		_notmuch_message_delete (message);
-	    else if (status == NOTMUCH_STATUS_DUPLICATE_MESSAGE_ID)
+	    
+		/* and reintroduce a ghost in its place */
+		ghost = _notmuch_message_create_for_message_id (notmuch, mid, &private_status);
+		if (private_status == NOTMUCH_PRIVATE_STATUS_SUCCESS) {
+		    /* this is deeply weird, and we should not have
+		       gotten into this state.  is there a better
+		       error message to return here? */
+		    status = NOTMUCH_STATUS_DUPLICATE_MESSAGE_ID;
+		} else if (private_status == NOTMUCH_PRIVATE_STATUS_NO_DOCUMENT_FOUND) {
+		    private_status = _notmuch_message_initialize_ghost (ghost, tid);
+		    if (! private_status) {
+			_notmuch_message_sync (ghost);
+			notmuch_message_destroy (ghost);
+		    }
+		}
+	    
+		status = COERCE_STATUS (private_status, "Error converting to ghost message");
+	    } else if (status == NOTMUCH_STATUS_DUPLICATE_MESSAGE_ID)
 		_notmuch_message_sync (message);
 
 	    notmuch_message_destroy (message);
-- 
2.8.0.rc3