PHP Warning: require(/path/to/vendor/composer/../symfony/polyfill-mbstring/bootstrap.php): failed to open stream: No such file or directory in /path/to/vendor/composer/autoload_real.php on line 66となったときの対応方法

• 環境
  • macOS Mojave バージョン10.14.4
  • PHP 7.3.1 (cli)
  • Composer version 1.8.0

事象 : Laravelのバージョンを確認しようとしたら怒られた。

$ php artisan -V
PHP Warning:  require(/path/to/vendor/composer/../symfony/polyfill-mbstring/bootstrap.php): failed to open stream: No such file or directory in /path/to/vendor/composer/autoload_real.php on line 66

Warning: require(/path/to/vendor/composer/../symfony/polyfill-mbstring/bootstrap.php): failed to open stream: No such file or directory in /path/to/vendor/composer/autoload_real.php on line 66
PHP Fatal error:  require(): Failed opening required '/path/to/vendor/composer/../symfony/polyfill-mbstring/bootstrap.php' (include_path='.:/usr/local/Cellar/php/7.3.1/share/php/pear') in /path/to/vendor/composer/autoload_real.php on line 66

Fatal error: require(): Failed opening required '/path/to/vendor/composer/../symfony/polyfill-mbstring/bootstrap.php' (include_path='.:/usr/local/Cellar/php/7.3.1/share/php/pear') in /path/to/vendor/composer/autoload_real.php on line 66

原因 : 必要なファイルがvenderディレクトリにないから

symfony - laravel on cpanel raise error for autoload_real.php on line 66 - Stack Overflow

対応 : composer updateする

$ composer update
Loading composer repositories with package information
Updating dependencies (including require-dev)
Package operations: 77 installs, 4 updates, 0 removals
... 省略 ...
  - Installing symfony/polyfill-mbstring (v1.11.0): Loading from cache
... 省略 ...
Writing lock file
Generating optimized autoload files
> Illuminate\Foundation\ComposerScripts::postAutoloadDump
> @php artisan package:discover --ansi
Discovered Package: beyondcode/laravel-dump-server
Discovered Package: fideloper/proxy
Discovered Package: laravel/nexmo-notification-channel
Discovered Package: laravel/slack-notification-channel
Discovered Package: laravel/tinker
Discovered Package: nesbot/carbon
Discovered Package: nunomaduro/collision
Package manifest generated successfully.

# 治りました。
$ php artisan -V
Laravel Framework 5.7.28

この間は問題なかったのに・・・なぜ？

ちょっと前の結果

$ php artisan -V
Laravel Framework 5.8.14

何かが更新でもされたのだろうか？それともなにかやったのを忘却しているのだろうか？