Why is Composer Reporting a PSR-4 Autoloading Error for My Class?

PHP Autoloading Error: "Class FooBarBaz does not comply with PSR-4 standard"

When running Composer commands like update, install, or dump-autoload, you may encounter a yellow deprecation notice:

Class Foo\Bar\Baz located in ./foo/bar/utility/baz.php does not comply with psr-4 autoloading standard. Skipping.

This error indicates that the class FooBarBaz does not follow the PSR-4 autoloading standard. Here are the steps to troubleshoot and resolve the issue:

Path Case

Ensure that the file path case matches the class name case. For example, foo/bar/Baz.php does not match AppBarBaz. Update the file path or class name to ensure they match.

File Name and Class Name Differences

Verify that the file name matches the class name accurately. Sometimes, the class name may not match the file name on disk (e.g., FooBar vs. foo-bar). Rename the class or file accordingly.

Nested Namespaces

If you have a nested namespace like Fizz\Buzz\, you need to declare the full namespace path in each affected file. For instance:

// src/Buzz/Dummy.php
namespace Fizz\Buzz\Buzz

class Dummy {}

Remember to update the namespace declaration and use statements for the affected classes and files.

Once these issues are addressed, composer autoloading will function correctly, and the deprecation notice will disappear. It is essential to pay attention to the error message, as it often provides precise guidance on the root cause of the autoloading error.

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