Demonstration of a strange PHP behavior concerning class definition order when nested traits are used

0-not-working.php

<?php
class MyClass
{
    use MyFirstTrait;
}

// This does not work. MyFirstTrait should use MySecondTrait, "Fatal error:
// Trait 'MyFirstTrait' not found" is raised instead.

trait MyFirstTrait
{
    use MySecondTrait;
    
    /**
     * @return string
     */
    public function first(): string
    {
        return __METHOD__;
    }
}

trait MySecondTrait {
    /**
     * @return string
     */
    public function second(): string
    {
        return __METHOD__;
    }
}

$myInstance = new MyClass;
var_dump($myInstance->first());

1-working.php

<?php
// This works. The use clause in MyFirstTrait is commented out, only one trait
// is used.

class MyClass
{
    use MyFirstTrait;
}

trait MyFirstTrait
{
//    use MySecondTrait;
  
    /**
     * @return string
     */
    public function first(): string
    {
        return __METHOD__;
    }
}

trait MySecondTrait {
    /**
     * @return string
     */
    public function second(): string
    {
        return __METHOD__;
    }
}

$myInstance = new MyClass;
var_dump($myInstance->first());

2-refactored-working.php

<?php
// This works. MyClass is now defined after the traits.

trait MyFirstTrait
{
    use MySecondTrait;

    /**
     * @return string
     */
    public function first(): string
    {
        return __METHOD__;
    }
}

trait MySecondTrait {
    /**
     * @return string
     */
    public function second(): string
    {
        return __METHOD__;
    }
}

class MyClass
{
    use MyFirstTrait;
}

$myInstance = new MyClass;
var_dump($myInstance->first());