This looks more like a bug. The second err is a valid redeclaration, and so should be checked for usage on it's own. Though the redeclaration through multiple a

This looks more like a bug. The second err is a valid redeclaration, and so should be checked for usage on it's own. Though the redeclaration through multiple assignment is itself a bit of a wart that the programmer hast to be wary of, so it may not be a big deal. In any case, the go compiler is very helpful in most cases, and better tooling can improve things further.