lib: add _notmuch_database_reopen

The main expected use is to recover from a Xapian::DatabaseChanged
exception.

lib/database-private.h

@@ -207,6 +207,10 @@ struct _notmuch_database {
     unsigned long revision;
     const char *uuid;
 
+    /* Keep track of the number of times the database has been re-opened
+     * (or other global invalidations of notmuch's caching)
+     */
+    unsigned long view;
     Xapian::QueryParser *query_parser;
     Xapian::TermGenerator *term_gen;
     Xapian::ValueRangeProcessor *value_range_processor;

lib/database.cc

@@ -951,6 +951,7 @@ notmuch_database_open_verbose (const char *path,
 
     notmuch->mode = mode;
     notmuch->atomic_nesting = 0;
+    notmuch->view = 1;
     try {
 	string last_thread_id;
 	string last_mod;
@@ -1133,6 +1134,28 @@ notmuch_database_close (notmuch_database_t *notmuch)
     return status;
 }
 
+notmuch_status_t
+_notmuch_database_reopen (notmuch_database_t *notmuch)
+{
+    if (notmuch->mode != NOTMUCH_DATABASE_MODE_READ_ONLY)
+	return NOTMUCH_STATUS_UNSUPPORTED_OPERATION;
+
+    try {
+	notmuch->xapian_db->reopen ();
+    } catch (const Xapian::Error &error) {
+	if (! notmuch->exception_reported) {
+	    _notmuch_database_log (notmuch, "Error: A Xapian exception reopening database: %s\n",
+				   error.get_msg ().c_str ());
+	    notmuch->exception_reported = TRUE;
+	}
+	return NOTMUCH_STATUS_XAPIAN_EXCEPTION;
+    }
+
+    notmuch->view++;
+
+    return NOTMUCH_STATUS_SUCCESS;
+}
+
 static int
 unlink_cb (const char *path,
 	   unused (const struct stat *sb),

lib/notmuch-private.h

@@ -192,6 +192,9 @@ _notmuch_message_id_compressed (void *ctx, const char *message_id);
 notmuch_status_t
 _notmuch_database_ensure_writable (notmuch_database_t *notmuch);
 
+notmuch_status_t
+_notmuch_database_reopen (notmuch_database_t *notmuch);
+
 void
 _notmuch_database_log (notmuch_database_t *notmuch,
 		       const char *format, ...);