Can the database be upgraded to a newer database version?
If this function returns TRUE, then the caller may call
notmuch_database_upgrade to upgrade the database. If the caller
does not upgrade an out-of-date database, then some functions may
fail with NOTMUCH_STATUS_UPGRADE_REQUIRED. This always returns
FALSE for a read-only database because there's no way to upgrade a
read-only database.
Can the database be upgraded to a newer database version?
If this function returns TRUE, then the caller may call notmuch_database_upgrade to upgrade the database. If the caller does not upgrade an out-of-date database, then some functions may fail with NOTMUCH_STATUS_UPGRADE_REQUIRED. This always returns FALSE for a read-only database because there's no way to upgrade a read-only database.