-- go.mod --
module m

go 1.12

require github.com/google/go-github v0.0.0-20181014183319-aa7423eb7970

-- main.go --
// +build ignore

package main

func main() {}

-- p.go --
package p

import "github.com/google/go-github/github"

var _ *github.Client

-- go.mod --
module m

go 1.12

require golang.org/x/tools v0.0.0-20190506145303-2d16b83fe98c

-- main.go --
package main

import (
	"fmt"
	"go/build"

	"golang.org/x/tools/go/packages"
)

func main() {
	for driver, f := range map[string]func(dir string) (name string, goFiles []string, _ error){
		"go/build":    useGoBuild,
		"go/packages": useGoPackages,
	} {
		name, goFiles, error := f("/tmp/target")

		fmt.Println(driver)
		fmt.Println("  error:", error)
		if error == nil {
			fmt.Println("  name:", name)
			fmt.Println("  goFiles:", goFiles)
		}
		fmt.Println()
	}
}

func useGoBuild(dir string) (name string, goFiles []string, _ error) {
	p, err := build.ImportDir(dir, 0)
	if err != nil {
		return "", nil, fmt.Errorf("build.ImportDir: %v", err)
	}
	return p.Name, p.GoFiles, nil
}

func useGoPackages(dir string) (name string, goFiles []string, _ error) {
	cfg := &packages.Config{
		Mode: packages.NeedName | packages.NeedFiles,
		Dir:  dir,
	}
	pkgs, err := packages.Load(cfg, ".")
	if err != nil {
		return "", nil, fmt.Errorf("packages.Load: %v", err)
	}
	if len(pkgs) != 1 {
		return "", nil, fmt.Errorf("got %d packages, want exactly 1 package", len(pkgs))
	}
	p := pkgs[0]
	if len(p.Errors) > 0 {
		return "", nil, fmt.Errorf("p.Errors: %v", p.Errors)
	}
	return p.Name, p.GoFiles, nil
}