Why PHP require autoload.php should be wrapped in is_readable()

When using Composer for PHP class autoloading, it is a good practice to wrap your require statement with an is_readable() check. Here are some notes on why this is an important thing to do.

if ( is_readable( __DIR__ . '/vendor/autoload.php' ) ) {
    require_once __DIR__ . '/vendor/autoload.php';
}

Your Autoload File Might Not Be There

When you run composer install from within your package directory, the /vendor directory will be added to the package directory and

require_once __DIR__ . '/vendor/autoload.php';

should work just fine.

However, if you load your package as a dependency (i.e. inside a project with a composer.json file at the root of the project), the files will instead be installed to a common /vendor directory in the project, NOT inside your package directory.

In this scenario (where your package is loading as a dependency within a project), the require_once statement above appearing in your package will throw a Fatal Error.

Note: In this scenario where your package is loaded as a dependency in a project, the project code should load its own autoloader to load files from the common /vendor directory.

Why Check Is Readable instead of File Exists

The is_readable() check does a file_exists() check and then checks that the file can be successfully read.

This is important because if the file does exist but the permissions are set such that your PHP code can not read the file, the file_exists() check will pass but when we try to require_once the file, it will fail with a fatal error.

Best Practices

Typically, you want to place the is_readable() / require_once code snippet both in the root file of you package and in the root file of your project.

if ( is_readable( __DIR__ . '/vendor/autoload.php' ) ) {
    require_once __DIR__ . '/vendor/autoload.php';
}

Sal Ferrarello (@salcode)

Sal is a PHP developer with a focus on the WordPress platform. He is a conference speaker with a background including Piano Player, Radio DJ, Magician/Juggler, Beach Photographer, and High School Math Teacher. Sal can be found professionally at WebDevStudios, where he works as a senior backend engineer.