Strange go build output

Build output

$ go build thingy
# thingy
src/thingy/main.go:6: imported and not used: "mypkg"
src/thingy/main.go:14: undefined: mypkg

Directory

$ find src

src/
src/thingy
src/thingy/thingy.go
src/mypkg
src/mypkg/mypkg.go

thingy.go

package main

import (                                                                          
        "flag"                                                                    
        "fmt"                                                                     
        "mypkg"                                                                
)                                                                                 
                                                                                  
func main() {                                                                     
        flag.Parse()                                                              
                                                                                  
        fmt.Println("Hello")                                                      
                                                                                  
        mypkg.Out(1, "Foo")                                                    
}