main.go:3:8: cannot find package "tmpprotos"

[Alexander Duda]

This happens if GOPATH is not set. On Mac OS the default behavior is to use ~/go if GOPATH is not set. I am not sure this is the case for all go installations.

Workaround:
set GOPATH

[Walter Schulze]

Yes. I guess I never considered a GOPATH that is not set.