Does it make sense to have two packages in the same directory?

You cannot have two packages per directory, hence the error. So the solution as @Larry Battle said to move your myproject.go to a new directory.

From How to write go code

Go code must be kept inside a workspace. A workspace is a directory hierarchy with three directories at its root:

src contains Go source files organized into packages (one package per directory),

pkg contains package objects, and

bin contains executable commands.

In most cases, no. However, there is an exception for unit tests.

Working Example:

Here are 2 different packages (mypackage and mypackage_test) in 1 directory (mypackage). The compiler will not complain about this.

mypackage folder:

mypackage/
  foo.go
  foo_test.go

mypackage/foo.go:

package mypackage

func Add(a int, b int) int {
    return a + b
}

mypackage/foo_test.go:

package mypackage_test

// Unit tests...

Rules:

1. The 2 packages must have the following names:

   • NameOfDirectory.
   • NameOfDirectory + _test.

2. The names of the files in the _test package must end with _test.go

If you're receiving a confusing compiler error along the lines of found packages "foo" and "bar", you've probably broken one or more of these rules.

Just move your packages inside a new folder within the same directory of main.go. Remember to import the new package from the reference of the $GOPATH.

Example:

user@user:~/p/go/test/so-multipack$ ls -R
.:
a  main.go

./a:
a.go
user@user:~/p/go/test/so-multipack$ cat main.go 
package main

import (
    "../so-multipack/a"
)
func main(){
    a.Hello()
}
user@user:~/p/go/test/so-multipack$ cat a/a.go 
package a
import (
    "fmt"
)
func Hello(){
    fmt.Println("hello from a")
}
user@user:~/p/go/test/so-multipack$ go run main.go 
hello from a
user@user:~/p/go/test/so-multipack$ go build 
user@user:~/p/go/test/so-multipack$ ls
a  main.go  so-multipack
user@user:~/p/go/test/so-multipack$ 

Useful link:

go build vs go build file.go