code: func PackageSourcePath(pkg string) (string, error) {
  	buildCtx := build.Default
  	buildCtx.GOPATH = envOr("GOPATH", build.Default.GOPATH) // Reevaluate each time to be nice to tests
  	wd, err := os.Getwd()
  	if err != nil {
  		wd = "."
  	}
  	p, err := buildCtx.Import(pkg, wd, 0)
  	if err != nil {
  		return "", err
  	}
  	return p.Dir, nil
  }
docs: // PackageSourcePath returns the absolute path to the given package source.