如何针对源代码和仅二进制包编译Go程序？

Background: I wrote a feature(in packageA) and don't want anyone see my code. So I installed it into .a file(packageA.a). I use it by below method:

package main  
import packageA  
func main(){  
    packageA.Run()  
}   

Then I do

go tool compile -I lib/ main.go
go tool link -o main -L main.o It can work.

But when I do this it doesn't work.
I wrote another feature(packageB) in $GOPATH/src/project/packageB
and update main.go

// main.go
package main
import (
    "packageA"
    _ "project/packageB"
)

func main(){
    packageA.Run()
}

exec go tool compile -I lib/ main.go

but error can't find import "packageB"

my directory layout

project  
     main.go  
     lib/  
        packageA.a  
     packageB  
        xxx.go  

Wanted to know if it's good practice to do that and what would be the best way to do that? go tool compile how to import .a file and source code?

Thanks sincerely in advance.