Please remove entry from /usr/portage/profiles/base/package.use.mask Qt Creator has just been updated to 4.15.1 which no longer needs or uses libclangformat-ide so the mask can be removed. (Removing clang support completely from Qt Creator severely damages / limits the IDE.) Ref https://bugs.gentoo.org/750527 Reproducible: Always
? already done in https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=6071107a60004a01f2a5a5085c2fc2f42014083f if you still see the mask, it must come from some local configuration on your machine.
Excellent - just a timing issue then.