dev-ruby/json fails test phase if rake-compiler is not installed * Running test phase for ruby18 ... (in /var/tmp/paludis/dev-ruby-json-1.2.0-r1/work/ruby18/json-1.2.0) WARNING: rake-compiler is not installed. You will not be able to build the json gem until you install it. Reproducible: Always
Since you provided no information at all, I can only close this bug, as it's not reproduced here.
FWIW I see that warning too, but since we build the json gem in a different way it is harmless.