Rector is Moving From YAML to PHP Configs - What Changes and How to Get Ready?

In July 2020, we started to move from the configuration in YAML to one defined in PHP. The YAML configuration is now deleted in Rector core and won't be supported next 0.8 release.

What benefits PHP brings, how the rule configuration changes, and how to prepare yourself?

You might have noticed the warning on Rector run:

This happens when you're using rector.yaml config in your project.

If you're already on rector.php, this message is gone.

Testing YAML to PHP in the Wild

It took around 3 weeks to switch configs, test out practical impacts, and resolve bugs related to method call values merging.

What is method call values merging? Rector uses multiple Symfony configs to keep sets separated, e.g., symfony40, symfony41, symfony42, etc. Each of them renames some classes, so they call configure() method with their values.


use Rector\Renaming\Rector\Name\RenameClassRector;

// first config
$services = $containerConfigurator->services();
    ->call('configure', [[
        RenameClassRector::OLD_TO_NEW_CLASSES => [
            'old_2' => 'new_2',

If you have 2 configs with same method call and same argument, only the latest one is used:

// another config
    ->call('configure', [[
        RenameClassRector::OLD_TO_NEW_CLASSES => [
            'old_1' => 'new_1',

We fixed this behavior from "override" to "merge" with custom file loader. It collects all the arguments and sets them once in the end before the container is compiled.

Now, even our demo runs on PHP configs:

Saying that yesterday we dropped YAML config support from Rector core.

How to Switch from rector.yaml to rector.php

What if you have a lot of custom setup in rector.yaml? Is there a list of changes that you need to do manually?

Don't worry. We're all lazy here. Migrify toolkit got you covered:

composer require migrify/config-transformer --dev

Then provide files/directories with YAML files you want to switch to PHP:

vendor/bin/config-transformer switch-format rector.yaml

What are Instant Benefits of rector.php?

There are 2 groups of benefits: one is related to general format switch - read about them in 10 Cool Features You Get after switching from YAML to PHP Configs.

The other is related to the smarter configuration of Rector rules.

Before, the configuration was done in an array-random-like manner.

    # rename class
            'OldClass': 'NewClass'

Be sure to bother your brain with memorizing $oldToNewClasses. And this is just key: value complexity - the simplest one.

What about more common nested configuration, e.g., constant rename?

            'SomeClass::OLD_CONSTANT': 'NEW_CONSTANT'
            # or...?
                'OLD_CONSTANT': 'NEW_CONSTANT'
            # or...?
                'OLD_CONSTANT': ['NEW_CONSTANT']
            # or...?
            ['SomeClass', 'OLD_CONSTANT']: 'NEW_CONSTANT'

This is a perfect example of "have an n-guesses, then rage quit" developer experience—freedom at its worst.

Value Objects Configuration FTW

There is a simple solution with PHP that could never be used in YAML - value objects.

final class ClassConstantRename
    // ...
    public function __construct(string $oldClass, string $oldConstant, string $newConstant)
        // ...

What Value is in Value Objects?

By only making single object, we got instantly high code quality for free:

  • type validation, string/int/constants
  • IDE autocompletes names of parameters, so we know what arguments are needed
  • a single line of configuration, no nesting to nesting to nesting to nesting

How do value objects look like in practice?

use Rector\Renaming\Rector\ClassConstFetch\RenameClassConstantRector;
use function Rector\SymfonyPhpConfig\inline_value_objects;
use Symfony\Component\DependencyInjection\Loader\Configurator\ContainerConfigurator;

return static function (ContainerConfigurator $containerConfigurator): void {
    $services = $containerConfigurator->services();

        ->call('configure', [[
            RenameClassConstantRector::CLASS_CONSTANT_RENAME => inline_value_objects([
                new ClassConstantRename('Cake\View\View', 'NAME_ELEMENT', 'TYPE_ELEMENT')

That's it. Use IDE autocomplete and value objects.

There is no need to look into the rule and look for the parameter name, the meaning of that particular key or value, if the key/value is required, optional, named, or implicit.

We're thinking of introducing rule <=> value object naming convention, so it gets even simpler:

  • RenameClassConstantRector for rule
  • RenameClassConstant for value object

Thanks to PHP, now all these optimizations are possible, and PHPStorm powers help us. And this is just a start.

Happy coding!