func checkMain(ctxt *build.Context) (bool, []string, error) {
	pkg, err := ctxt.ImportDir(*rootDir, 0)
	if err != nil {
		return false, nil, fmt.Errorf("unable to analyze source: %v", err)
	}
	if !pkg.IsCommand() {
		errorf("Your app's package needs to be changed from %q to \"main\".\n", pkg.Name)
	}
	// Search for a "func main"
	var hasMain bool
	var appFiles []string
	for _, f := range pkg.GoFiles {
		n := filepath.Join(*rootDir, f)
		appFiles = append(appFiles, n)
		if hasMain, err = readFile(n); err != nil {
			return false, nil, fmt.Errorf("error parsing %q: %v", n, err)
		}
	}
	return hasMain, appFiles, nil
}
func checkMain(ctxt *build.Context) (bool, []string, error) {
	pkg, err := ctxt.ImportDir(*rootDir, 0)
	if err != nil {
		return false, nil, fmt.Errorf("unable to analyze source: %v", err)
	}
	if !pkg.IsCommand() {
		errorf("Your app's package needs to be changed from %q to \"main\".\n", pkg.Name)
	}
	// Search for a "func main"
	var hasMain bool
	var appFiles []string
	for _, f := range pkg.GoFiles {
		n := filepath.Join(*rootDir, f)
		appFiles = append(appFiles, n)
		if hasMain, err = readFile(n); err != nil {
			return false, nil, fmt.Errorf("error parsing %q: %v", n, err)
		}
	}
	return hasMain, appFiles, nil
}
// checkMain verifies that there is a single "main" function.
// It also returns a list of all Go source files in the app.