One that definitely happens is if, for instance, a library returns datastore.ErrNoSuchEntity, but vendored the "datastore" package. If you have your own version of "datastore" then you do "err == datastore.ErrNoSuchEntity" and it's false, because there are two copies of ErrNoSuchEntity in memory.
This seems pretty solvable though. If you vendor a package, you need to make sure you don't do this. If we do gb-style everyone vendors stuff themselves (not in libraries), then it's not an issue.
This seems pretty solvable though. If you vendor a package, you need to make sure you don't do this. If we do gb-style everyone vendors stuff themselves (not in libraries), then it's not an issue.