or, submit a ticket requesting the port adds macports-clang-3.9 and macports-clang-4.0 to the compiler blacklist. Where can I submit it?
trac https://trac.macports.org/wiki/Tickets
Yes, the warning is mis-leading Error: clang-4.0 has been replaced by clang-8.0; please install that instead. this does not actually mean clang-8.0 is not already installed.... What it really should say is 'please configure port <foo-bar> to use clang-8.0 instead' That would be less confusing indeed. Can that be made the message?
Not easily. The message is generated by the obsolete port group, which is used in a number of scenarios, for some of which the currently message does make sense.
Chris