Hi John,
Your guess is right, I am interested in a reduced example outlining the different behaviour of template instantiation/specialization in clang vs gcc leading to the error. So yes the test should look for the specific clang error message "error: no matching function for call to 'get'" while gcc is OK with the code. Sorry for not writing this.
I'm not sure about the -w, though. The original code compiles without any warning on gcc so ideally this behaviour should be kept in the reduced example. It may make reducing much harder, though, so we could probably start with -w and see how it goes.
Yaron