--- /dev/null
+/* thread-fp.cc - "thread:" field processor glue
+ *
+ * This file is part of notmuch.
+ *
+ * Copyright © 2018 David Bremner
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see https://www.gnu.org/licenses/ .
+ *
+ * Author: David Bremner <david@tethera.net>
+ */
+
+#include "database-private.h"
+#include "thread-fp.h"
+#include <iostream>
+
+#if HAVE_XAPIAN_FIELD_PROCESSOR
+
+Xapian::Query
+ThreadFieldProcessor::operator() (const std::string & str)
+{
+ notmuch_status_t status;
+ const char *thread_prefix = _find_prefix ("thread");
+
+ if (str.at (0) == '{') {
+ if (str.size () <= 1 || str.at (str.size () - 1) != '}') {
+ throw Xapian::QueryParserError ("missing } in '" + str + "'");
+ } else {
+ std::string subquery_str = str.substr (1, str.size () - 2);
+ notmuch_query_t *subquery = notmuch_query_create (notmuch, subquery_str.c_str ());
+ notmuch_messages_t *messages;
+ std::set<std::string> terms;
+
+ if (! subquery)
+ throw Xapian::QueryParserError ("failed to create subquery for '" + subquery_str + "'");
+
+ status = notmuch_query_search_messages (subquery, &messages);
+ if (status)
+ throw Xapian::QueryParserError ("failed to search messages for '" + subquery_str + "'");
+
+ for (; notmuch_messages_valid (messages); notmuch_messages_move_to_next (messages)) {
+ std::string term = thread_prefix;
+ notmuch_message_t *message;
+ message = notmuch_messages_get (messages);
+ term += notmuch_message_get_thread_id (message);
+ terms.insert (term);
+ }
+ return Xapian::Query (Xapian::Query::OP_OR, terms.begin (), terms.end ());
+ }
+ } else {
+ /* literal thread id */
+ std::string term = thread_prefix + str;
+ return Xapian::Query (term);
+ }
+
+}
+#endif