// and returns the path to the package source relative to $GOROOT (or $GOPATH).
func pkgPath() (importPath string, isStd bool, modPath, modDir string, err error) {
	errorf := func(format string, args ...any) (string, bool, string, string, error) {
		return "", false, "", "", fmt.Errorf(format, args...)
	}
	goTool, err := goTool()
	if err != nil {
		return errorf("%w", err)
	}