Store thread ids for messages that we haven't seen yet

This allows us to thread messages even when we receive them out of
order, or never receive the root.

The thread ids for messages that aren't present but are referred to are
stored as metadata in the database and then retrieved if we ever get
that message.

When determining the thread id for a message we also check for this
metadata so that we can thread descendants of a message together before
we receive it.

Edited by Carl Worth <cworth@cworth.org>: Split this portion of the
commit from the earlier-applied portion adding test cases.

diff --git a/lib/database.cc b/lib/database.cc
index c91e97c125940b384a3bd24963df6cbeedd88acb..92234ff42ddc398dc7647c55d295368af940a431 100644 (file)
--- a/lib/database.cc
+++ b/lib/database.cc
@@ -1111,6 +1111,31 @@ notmuch_database_get_directory (notmuch_database_t *notmuch,
     return _notmuch_directory_create (notmuch, path, &status);
 }
 
+static const char *
+_notmuch_database_generate_thread_id (notmuch_database_t *notmuch)
+{
+    /* 16 bytes (+ terminator) for hexadecimal representation of
+     * a 64-bit integer. */
+    static char thread_id[17];
+    Xapian::WritableDatabase *db;
+
+    db = static_cast <Xapian::WritableDatabase *> (notmuch->xapian_db);
+
+    notmuch->last_thread_id++;
+
+    sprintf (thread_id, "%016" PRIx64, notmuch->last_thread_id);
+
+    db->set_metadata ("last_thread_id", thread_id);
+
+    return thread_id;
+}
+
+static char *
+_get_metadata_thread_id_key (void *ctx, const char *message_id)
+{
+    return talloc_asprintf (ctx, "thread_id_%s", message_id);
+}
+
 /* Find the thread ID to which the message with 'message_id' belongs.
  *
  * Returns NULL if no message with message ID 'message_id' is in the
@@ -1127,8 +1152,25 @@ _resolve_message_id_to_thread_id (notmuch_database_t *notmuch,
     const char *ret = NULL;
 
     message = notmuch_database_find_message (notmuch, message_id);
-    if (message == NULL)
-       goto DONE;
+    /* If we haven't seen that message yet then check if we have already
+     * generated a dummy id for it and stored it in the metadata.
+     * If not then we generate a new thread id.
+     * This ensures that we can thread messages even when we haven't received
+     * the root (yet?)
+     */
+    if (message == NULL) {
+        Xapian::WritableDatabase *db = static_cast <Xapian::WritableDatabase *> (notmuch->xapian_db);
+        char * metadata_key = _get_metadata_thread_id_key (ctx, message_id);
+        string thread_id = notmuch->xapian_db->get_metadata(metadata_key);
+        if (thread_id.empty()) {
+            ret = _notmuch_database_generate_thread_id(notmuch);
+            db->set_metadata(metadata_key, ret);
+        } else {
+            ret = thread_id.c_str();
+        }
+        talloc_free (metadata_key);
+        goto DONE;
+    }
 
     ret = talloc_steal (ctx, notmuch_message_get_thread_id (message));
 
@@ -1295,25 +1337,6 @@ _notmuch_database_link_message_to_children (notmuch_database_t *notmuch,
     return ret;
 }
 
-static const char *
-_notmuch_database_generate_thread_id (notmuch_database_t *notmuch)
-{
-    /* 16 bytes (+ terminator) for hexadecimal representation of
-     * a 64-bit integer. */
-    static char thread_id[17];
-    Xapian::WritableDatabase *db;
-
-    db = static_cast <Xapian::WritableDatabase *> (notmuch->xapian_db);
-
-    notmuch->last_thread_id++;
-
-    sprintf (thread_id, "%016" PRIx64, notmuch->last_thread_id);
-
-    db->set_metadata ("last_thread_id", thread_id);
-
-    return thread_id;
-}
-
 /* Given a (mostly empty) 'message' and its corresponding
  * 'message_file' link it to existing threads in the database.
  *
@@ -1337,6 +1360,19 @@ _notmuch_database_link_message (notmuch_database_t *notmuch,
 {
     notmuch_status_t status;
     const char *thread_id = NULL;
+    char *metadata_key = _get_metadata_thread_id_key (message,
+            notmuch_message_get_message_id (message));
+    /* Check if we have already seen related messages to this one.
+     * If we have then use the thread_id that we stored at that time.
+     */
+    string stored_id = notmuch->xapian_db->get_metadata (metadata_key);
+    if (!stored_id.empty()) {
+        Xapian::WritableDatabase *db = static_cast <Xapian::WritableDatabase *> (notmuch->xapian_db);
+        db->set_metadata (metadata_key, "");
+        thread_id = stored_id.c_str();
+        _notmuch_message_add_term (message, "thread", thread_id);
+    }
+    talloc_free (metadata_key);
 
     status = _notmuch_database_link_message_to_parents (notmuch, message,
                                                        message_file,