/etc/cron.daily/mlocate says "/bin/sh" in the shebang line, but uses bash-specific features - the "source" keyword is known to bash only, we can replace it with a dot which all POSIX shells understand. Normally /bin/sh always symlinks to bash in Gentoo, but it seems from bug #214817 that they're in the process of introducing app-admin/eselect-sh to tree (now in sunrise overlay), which will allow users to switch to dash (which Ubuntu and Debian persons have used as the default /bin/sh for years) or something alike. So I think it's time to get this fixed before many users do that. Reproducible: Always
Thanks for your hint, I fixed it in mlocate-0.22.2-r1