in pkg/rbeconfigsgen/rbeconfigsgen.go [405:429]
func appendCppEnv(env []string, o *Options) ([]string, error) {
	for k, v := range o.CppGenEnv {
		env = append(env, fmt.Sprintf("%s=%s", k, v))
	}
	if len(o.CppGenEnvJSON) == 0 {
		return env, nil
	}
	blob, err := ioutil.ReadFile(o.CppGenEnvJSON)
	if err != nil {
		return nil, fmt.Errorf("unable to read JSON file %q to read C++ config generation environment variables from: %w", o.CppGenEnvJSON, err)
	}
	e := map[string]string{}
	if err := json.Unmarshal(blob, &e); err != nil {
		return nil, fmt.Errorf("unable to parse file %q as a JSON string -> string dictionary: %w", o.CppGenEnvJSON, err)
	}
	for k, v := range e {
		env = append(env, fmt.Sprintf("%s=%s", k, v))
	}
	return env, nil
}