feature #31287 [Config] Introduce find method in ArrayNodeDefinition to ease configuration tree manipulation (jschaedl)

This PR was squashed before being merged into the 4.4 branch (closes #31287).

Discussion
----------

[Config] Introduce find method in ArrayNodeDefinition to ease configuration tree manipulation

| Q             | A
| ------------- | ---
| Branch?       | 4.4
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no <!-- don't forget to update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Tests pass?   | yes    <!-- please add some, will be required by reviewers -->
| Fixed tickets | #27534   <!-- #-prefixed issue number(s), if any -->
| License       | MIT
| Doc PR        | tbd.

### Description

This PR introduces a new `find(string $nodePath)`method in the `ArrayNodeDefinition` class, which helps you finding the right node to prepend configuration to ease configuration tree manipulation.

### How to use it
```php
class Configuration implements ConfigurationInterface
{
    public function getConfigTreeBuilder()
    {
        ...

        $rootNode
            ->children()
                ->arrayNode('social_media_channels')
                    ->children()
                        ->booleanNode('enable')->end()
                        ->arrayNode('twitter')->end()
                        ->arrayNode('facebook')->end()
                        ->arrayNode('instagram')->end()
                    ->end()
                ->end()
            ->end()
        ;

        $this->changeSocialMediaChannelConfiguration($rootNode->find('social_media_channels.enable'));
        $this->addTwitterConfiguration($rootNode->find('social_media_channels.twitter'));
        $this->addFacebookConfiguration($rootNode->find('social_media_channels.facebook'));
        $this->addInstagramConfiguration($rootNode->find('social_media_channels.instagram'));

        return $treeBuilder;
    }

    private function changeSocialMediaChannelConfiguration(NodeDefinition $node)
    {
        $node
            ->defaultTrue()
        ;
    }

    private function addTwitterConfiguration(NodeDefinition $node)
    {
        $node
            ->children()
                ->integerNode('client_id')->end()
                ->scalarNode('client_secret')->end()
            ->end()
        ;
    }

    private function addFacebookConfiguration(NodeDefinition $node)
    {
        $node
            ->children()
                ->integerNode('client_id')->end()
                ->scalarNode('client_secret')->end()
            ->end()
        ;
    }

    private function addInstagramConfiguration(NodeDefinition $node)
    {
        $node
            ->children()
                ->integerNode('client_id')->end()
                ->scalarNode('client_secret')->end()
            ->end()
        ;
    }
}

```

Commits
-------

e3b248aee0 [Config] Introduce find method in ArrayNodeDefinition to ease configuration tree manipulation

src/Symfony/Component/Config/Definition/Builder/ArrayNodeDefinition.php

@@ -523,4 +523,26 @@ class ArrayNodeDefinition extends NodeDefinition implements ParentNodeDefinition
     {
         return $this->children;
     }
+
+    /**
+     * Finds a node defined by the given $nodePath.
+     *
+     * @param string $nodePath The path of the node to find. e.g "doctrine.orm.mappings"
+     */
+    public function find(string $nodePath): NodeDefinition
+    {
+        $firstPathSegment = (false === $pathSeparatorPos = strpos($nodePath, $this->pathSeparator))
+            ? $nodePath
+            : substr($nodePath, 0, $pathSeparatorPos);
+
+        if (null === $node = ($this->children[$firstPathSegment] ?? null)) {
+            throw new \RuntimeException(sprintf('Node with name "%s" does not exist in the current node "%s".', $firstPathSegment, $this->name));
+        }
+
+        if (false === $pathSeparatorPos) {
+            return $node;
+        }
+
+        return $node->find(substr($nodePath, $pathSeparatorPos + \strlen($this->pathSeparator)));
+    }
 }

src/Symfony/Component/Config/Tests/Definition/Builder/ArrayNodeDefinitionTest.php

@@ -13,6 +13,8 @@ namespace Symfony\Component\Config\Tests\Definition\Builder;
 
 use PHPUnit\Framework\TestCase;
 use Symfony\Component\Config\Definition\Builder\ArrayNodeDefinition;
+use Symfony\Component\Config\Definition\Builder\BooleanNodeDefinition;
+use Symfony\Component\Config\Definition\Builder\NodeDefinition;
 use Symfony\Component\Config\Definition\Builder\ScalarNodeDefinition;
 use Symfony\Component\Config\Definition\Exception\InvalidDefinitionException;
 use Symfony\Component\Config\Definition\Processor;
@@ -357,6 +359,85 @@ class ArrayNodeDefinitionTest extends TestCase
         $node->getNode()->finalize([]);
     }
 
+    public function testFindShouldThrowExceptionIfNodeDoesNotExistInRootNode()
+    {
+        $this->expectException(\RuntimeException::class);
+        $this->expectExceptionMessage('Node with name "child" does not exist in the current node "root".');
+
+        $rootNode = new ArrayNodeDefinition('root');
+        $rootNode
+            ->children()
+                ->arrayNode('social_media_channels')->end()
+            ->end()
+        ;
+
+        $rootNode->find('child');
+    }
+
+    public function testFindShouldHandleComplexConfigurationProperly()
+    {
+        $rootNode = new ArrayNodeDefinition('root');
+        $rootNode
+            ->children()
+                ->arrayNode('social_media_channels')
+                    ->children()
+                        ->booleanNode('enable')->end()
+                        ->arrayNode('twitter')->end()
+                        ->arrayNode('facebook')->end()
+                        ->arrayNode('instagram')
+                            ->children()
+                                ->booleanNode('enable')->end()
+                                ->arrayNode('accounts')->end()
+                            ->end()
+                    ->end()
+                ->end()
+                ->append(
+                    $mailerNode = (new ArrayNodeDefinition('mailer'))
+                        ->children()
+                            ->booleanNode('enable')->end()
+                            ->arrayNode('transports')->end()
+                        ->end()
+                )
+            ->end()
+        ;
+
+        $this->assertNode('social_media_channels', ArrayNodeDefinition::class, $rootNode->find('social_media_channels'));
+        $this->assertNode('enable', BooleanNodeDefinition::class, $rootNode->find('social_media_channels.enable'));
+        $this->assertNode('twitter', ArrayNodeDefinition::class, $rootNode->find('social_media_channels.twitter'));
+        $this->assertNode('facebook', ArrayNodeDefinition::class, $rootNode->find('social_media_channels.facebook'));
+        $this->assertNode('instagram', ArrayNodeDefinition::class, $rootNode->find('social_media_channels.instagram'));
+        $this->assertNode('enable', BooleanNodeDefinition::class, $rootNode->find('social_media_channels.instagram.enable'));
+        $this->assertNode('accounts', ArrayNodeDefinition::class, $rootNode->find('social_media_channels.instagram.accounts'));
+
+        $this->assertNode('enable', BooleanNodeDefinition::class, $mailerNode->find('enable'));
+        $this->assertNode('transports', ArrayNodeDefinition::class, $mailerNode->find('transports'));
+    }
+
+    public function testFindShouldWorkProperlyForNonDefaultPathSeparator()
+    {
+        $rootNode = new ArrayNodeDefinition('root');
+        $rootNode
+            ->setPathSeparator('.|')
+            ->children()
+            ->arrayNode('mailer.configuration')
+                ->children()
+                    ->booleanNode('enable')->end()
+                    ->arrayNode('transports')->end()
+                ->end()
+            ->end()
+        ;
+
+        $this->assertNode('mailer.configuration', ArrayNodeDefinition::class, $rootNode->find('mailer.configuration'));
+        $this->assertNode('enable', BooleanNodeDefinition::class, $rootNode->find('mailer.configuration.|enable'));
+        $this->assertNode('transports', ArrayNodeDefinition::class, $rootNode->find('mailer.configuration.|transports'));
+    }
+
+    protected function assertNode(string $expectedName, string $expectedType, NodeDefinition $actualNode): void
+    {
+        $this->assertInstanceOf($expectedType, $actualNode);
+        $this->assertSame($expectedName, $this->getField($actualNode, 'name'));
+    }
+
     protected function getField($object, $field)
     {
         $reflection = new \ReflectionProperty($object, $field);