RHEL-7.4 update updated vala to 0.34.6-1.el7 but xfce4-vala has: vala <= 0:0.26.99 I guess it needs update to work with new vala. Upgrade is ugrent because installed xfce4-vala blocks system updates.
xfce4-vala-4.10.3-17.el7 has been submitted as an update to Fedora EPEL 7. https://bodhi.fedoraproject.org/updates/FEDORA-EPEL-2017-a78d7e3eb4
xfce4-vala-4.10.3-17.el7 has been pushed to the Fedora EPEL 7 testing repository. If problems still persist, please make note of it in this bug report. See https://fedoraproject.org/wiki/QA:Updates_Testing for instructions on how to install test updates. You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-EPEL-2017-a78d7e3eb4
xfce4-vala-4.10.3-17.el7 has been pushed to the Fedora EPEL 7 stable repository. If problems still persist, please make note of it in this bug report.