Are you building on 18.04? If so, you’ll be installing libraries which are not compatible with the libc from the core snap (which is still on 16.04).
Libc will come from the core snap, so you don’t have to add it to your stage packages. If you’re building on 16.04 against the default core snap, there probably won’t be any real problem, but it is unnecessary and could create complications if the default core snap changes in the future.
Ok. I had no idea there was an exception for glibc.
Perhaps the warning should be rephrased to make that clear? @jdstrand, @niemeyer.
libc6 has been staged into the snap: You don’t have to do this. It is already bundled (by the “default core snap”). Only do this if you know what what you are doing.