According to the docs
revert() will not consume any gas:
Note that assert-style exceptions consume all gas available to the call, while revert-style exceptions will not consume any gas starting from the Metropolis release.
But i frequently read that
revert() will refund unused gas, e.g. in this answer.
I'm thinking refunding ALL gas will open gates for DOS-attacks, so I'm assuming only unused gas will be refunded. But I would like confirmation :-)