config/config.go
func flattenKeys(m map[string]interface{}, keys []string) {
	keyMap := make(map[string]struct{})
	for _, key := range keys {
		keyMap[key] = struct{}{}
	}

	var flatten func(map[string]interface{}, string)
	flatten = func(m map[string]interface{}, parent string) {
		for k, v := range m {
			// Calculate the map key, since it could include a parent.
			mapKey := k
			if parent != "" {
				mapKey = parent + "." + k
			}

			if _, ok := keyMap[mapKey]; !ok {
				continue
			}

			switch typed := v.(type) {
			case []map[string]interface{}:
				if len(typed) > 0 {
					last := typed[len(typed)-1]
					flatten(last, mapKey)
					m[k] = last
				} else {
					m[k] = nil
				}
			case map[string]interface{}:
				flatten(typed, mapKey)
				m[k] = typed
			default:
				m[k] = v
			}
		}
	}

	flatten(m, "")
}
func flattenKeys(m map[string]interface{}, keys []string) {
	keyMap := make(map[string]struct{})
	for _, key := range keys {
		keyMap[key] = struct{}{}
	}

	var flatten func(map[string]interface{}, string)
	flatten = func(m map[string]interface{}, parent string) {
		for k, v := range m {
			// Calculate the map key, since it could include a parent.
			mapKey := k
			if parent != "" {
				mapKey = parent + "." + k
			}

			if _, ok := keyMap[mapKey]; !ok {
				continue
			}

			switch typed := v.(type) {
			case []map[string]interface{}:
				if len(typed) > 0 {
					last := typed[len(typed)-1]
					flatten(last, mapKey)
					m[k] = last
				} else {
					m[k] = nil
				}
			case map[string]interface{}:
				flatten(typed, mapKey)
				m[k] = typed
			default:
				m[k] = v
			}
		}
	}

	flatten(m, "")
}
// flattenKeys is a function that takes a map[string]interface{} and recursively
// flattens any keys that are a []map[string]interface{} where the key is in the
// given list of keys.