% cat foo.go
package main
//go:generate msgp -tests=false -io=false
type A int
type B = A
func main() {
}
% go generate .
======== MessagePack Code Generator =======
>>> Input: "foo.go"
>>> Wrote and formatted "foo_gen.go"
% go build .
./foo_gen.go:38:12: A.MarshalMsg redeclared in this block
previous declaration at ./foo_gen.go:10:6
./foo_gen.go:45:13: (*A).UnmarshalMsg redeclared in this block
previous declaration at ./foo_gen.go:17:6
./foo_gen.go:60:12: A.Msgsize redeclared in this block
previous declaration at ./foo_gen.go:32:6
% go version
go version go1.12 linux/amd64
%
