[Config][FrameworkBundle] Allow to dump extension config reference sub path

src/Symfony/Bundle/FrameworkBundle/Command/ConfigDumpReferenceCommand.php

@@ -37,6 +37,7 @@ class ConfigDumpReferenceCommand extends AbstractConfigCommand
             ->setName('config:dump-reference')
             ->setDefinition(array(
                 new InputArgument('name', InputArgument::OPTIONAL, 'The Bundle name or the extension alias'),
+                new InputArgument('path', InputArgument::OPTIONAL, 'The configuration option path'),
                 new InputOption('format', null, InputOption::VALUE_REQUIRED, 'The output format (yaml or xml)', 'yaml'),
             ))
             ->setDescription('Dumps the default configuration for an extension')
@@ -54,6 +55,10 @@ this is either <comment>yaml</comment> or <comment>xml</comment>.
 When the option is not provided, <comment>yaml</comment> is used.
 
   <info>php %command.full_name% FrameworkBundle --format=xml</info>
+  
+For dumping a specific option, add its path as second argument (only available for the yaml format):
+
+  <info>php %command.full_name% framework profiler.matcher</info>
 
 EOF
             )
@@ -71,7 +76,10 @@ EOF
 
         if (null === $name = $input->getArgument('name')) {
             $this->listBundles($io);
-            $io->comment('Provide the name of a bundle as the first argument of this command to dump its default configuration. (e.g. <comment>config:dump-reference FrameworkBundle</comment>)');
+            $io->comment(array(
+                'Provide the name of a bundle as the first argument of this command to dump its default configuration. (e.g. <comment>config:dump-reference FrameworkBundle</comment>)',
+                'For dumping a specific option, add its path as the second argument of this command. (e.g. <comment>config:dump-reference FrameworkBundle profiler.matcher</comment> to dump the <comment>framework.profiler.matcher</comment> configuration)',
+            ));
 
             return;
         }
@@ -82,13 +90,26 @@ EOF
 
         $this->validateConfiguration($extension, $configuration);
 
+        $format = $input->getOption('format');
+        $path = $input->getArgument('path');
+
+        if ($path !== null && 'yaml' !== $format) {
+            $io->error('The "path" option is only available for the "yaml" format.');
+
+            return 1;
+        }
+
         if ($name === $extension->getAlias()) {
             $message = sprintf('Default configuration for extension with alias: "%s"', $name);
         } else {
             $message = sprintf('Default configuration for "%s"', $name);
         }
 
-        switch ($input->getOption('format')) {
+        if ($path !== null) {
+            $message .= sprintf(' at path "%s"', $path);
+        }
+
+        switch ($format) {
             case 'yaml':
                 $io->writeln(sprintf('# %s', $message));
                 $dumper = new YamlReferenceDumper();
@@ -102,6 +123,6 @@ EOF
                 throw new \InvalidArgumentException('Only the yaml and xml formats are supported.');
         }
 
-        $io->writeln($dumper->dump($configuration, $extension->getNamespace()));
+        $io->writeln(null === $path ? $dumper->dump($configuration, $extension->getNamespace()) : $dumper->dumpAtPath($configuration, $path));
     }
 }

src/Symfony/Bundle/FrameworkBundle/Tests/Functional/Bundle/TestBundle/DependencyInjection/Config/CustomConfig.php

@@ -18,6 +18,13 @@ class CustomConfig
         $rootNode
             ->children()
                 ->scalarNode('custom')->end()
+                ->arrayNode('array')
+                    ->children()
+                        ->scalarNode('child1')->end()
+                        ->scalarNode('child2')->end()
+                        ->end()
+                    ->end()
+                ->end()
             ->end()
         ;
     }

src/Symfony/Bundle/FrameworkBundle/Tests/Functional/ConfigDumpReferenceCommandTest.php

@@ -40,6 +40,39 @@ class ConfigDumpReferenceCommandTest extends WebTestCase
         $this->assertContains('    custom:', $tester->getDisplay());
     }
 
+    public function testDumpAtPath()
+    {
+        $tester = $this->createCommandTester();
+        $ret = $tester->execute(array(
+            'name' => 'test',
+            'path' => 'array',
+        ));
+
+        $this->assertSame(0, $ret, 'Returns 0 in case of success');
+        $this->assertSame(<<<'EOL'
+# Default configuration for extension with alias: "test" at path "array"
+array:
+    child1:               ~
+    child2:               ~
+
+
+EOL
+            , $tester->getDisplay(true));
+    }
+
+    public function testDumpAtPathXml()
+    {
+        $tester = $this->createCommandTester();
+        $ret = $tester->execute(array(
+            'name' => 'test',
+            'path' => 'array',
+            '--format' => 'xml',
+        ));
+
+        $this->assertSame(1, $ret);
+        $this->assertContains('[ERROR] The "path" option is only available for the "yaml" format.', $tester->getDisplay());
+    }
+
     /**
      * @return CommandTester
      */

src/Symfony/Bundle/FrameworkBundle/composer.json

@@ -20,7 +20,7 @@
         "symfony/cache": "~3.3",
         "symfony/class-loader": "~3.2",
         "symfony/dependency-injection": "~3.3",
-        "symfony/config": "~2.8|~3.0",
+        "symfony/config": "~3.3",
         "symfony/event-dispatcher": "~2.8|~3.0",
         "symfony/http-foundation": "~3.1",
         "symfony/http-kernel": "~3.3",

src/Symfony/Component/Config/Definition/Dumper/YamlReferenceDumper.php

@@ -33,6 +33,32 @@ class YamlReferenceDumper
         return $this->dumpNode($configuration->getConfigTreeBuilder()->buildTree());
     }
 
+    public function dumpAtPath(ConfigurationInterface $configuration, $path)
+    {
+        $rootNode = $node = $configuration->getConfigTreeBuilder()->buildTree();
+
+        foreach (explode('.', $path) as $step) {
+            if (!$node instanceof ArrayNode) {
+                throw new \UnexpectedValueException(sprintf('Unable to find node at path "%s.%s"', $rootNode->getName(), $path));
+            }
+
+            /** @var NodeInterface[] $children */
+            $children = $node instanceof PrototypedArrayNode ? $this->getPrototypeChildren($node) : $node->getChildren();
+
+            foreach ($children as $child) {
+                if ($child->getName() === $step) {
+                    $node = $child;
+
+                    continue 2;
+                }
+            }
+
+            throw new \UnexpectedValueException(sprintf('Unable to find node at path "%s.%s"', $rootNode->getName(), $path));
+        }
+
+        return $this->dumpNode($node);
+    }
+
     public function dumpNode(NodeInterface $node)
     {
         $this->reference = '';

src/Symfony/Component/Config/Tests/Definition/Dumper/YamlReferenceDumperTest.php

@@ -25,6 +25,61 @@ class YamlReferenceDumperTest extends \PHPUnit_Framework_TestCase
         $this->assertEquals($this->getConfigurationAsString(), $dumper->dump($configuration));
     }
 
+    public function provideDumpAtPath()
+    {
+        return array(
+            'Regular node' => array('scalar_true', <<<EOL
+scalar_true:          true
+EOL
+            ),
+            'Array node' => array('array', <<<EOL
+# some info
+array:
+    child1:               ~
+    child2:               ~
+
+    # this is a long
+    # multi-line info text
+    # which should be indented
+    child3:               ~ # Example: example setting
+EOL
+            ),
+            'Regular nested' => array('array.child2', <<<EOL
+child2:               ~
+EOL
+            ),
+            'Prototype' => array('cms_pages.page', <<<EOL
+# Prototype
+page:
+
+    # Prototype
+    locale:
+        title:                ~ # Required
+        path:                 ~ # Required
+EOL
+            ),
+            'Nested prototype' => array('cms_pages.page.locale', <<<EOL
+# Prototype
+locale:
+    title:                ~ # Required
+    path:                 ~ # Required
+EOL
+            ),
+        );
+    }
+
+    /**
+     * @dataProvider provideDumpAtPath
+     */
+    public function testDumpAtPath($path, $expected)
+    {
+        $configuration = new ExampleConfiguration();
+
+        $dumper = new YamlReferenceDumper();
+
+        $this->assertSame(trim($expected), trim($dumper->dumpAtPath($configuration, $path)));
+    }
+
     private function getConfigurationAsString()
     {
         return <<<'EOL'