feature #20361 [Config] Enable cannotBeEmpty along with requiresAtLeastOneElement (ro0NL)

This PR was squashed before being merged into the 3.4 branch (closes #20361).

Discussion
----------

[Config] Enable cannotBeEmpty along with requiresAtLeastOneElement

| Q | A |
| --- | --- |
| Branch? | "master" |
| Bug fix? | no |
| New feature? | yes |
| BC breaks? | no |
| Deprecations? | no |
| Tests pass? | yes
| Fixed tickets | #20356 |
| License | MIT |
| Doc PR | reference to the documentation PR, if any |

As @vudaltsov mentioned, we ignore any calls to `ArrayNodeDefinition::cannotBeEmpty`, which can lead to unexpected behavior. Imo. all subclasses should follow the base API.

Commits
-------

d40e7e4c2d [Config] Enable cannotBeEmpty along with requiresAtLeastOneElement

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

@@ -428,7 +428,7 @@ class ArrayNodeDefinition extends NodeDefinition implements ParentNodeDefinition
                 $node->setKeyAttribute($this->key, $this->removeKeyItem);
             }
 
-            if (true === $this->atLeastOne) {
+            if (true === $this->atLeastOne || false === $this->allowEmptyValue) {
                 $node->setMinNumberOfElements(1);
             }
 
@@ -490,6 +490,12 @@ class ArrayNodeDefinition extends NodeDefinition implements ParentNodeDefinition
             );
         }
 
+        if (false === $this->allowEmptyValue) {
+            throw new InvalidDefinitionException(
+                sprintf('->cannotBeEmpty() is not applicable to concrete nodes at path "%s"', $path)
+            );
+        }
+
         if (true === $this->atLeastOne) {
             throw new InvalidDefinitionException(
                 sprintf('->requiresAtLeastOneElement() is not applicable to concrete nodes at path "%s"', $path)

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

@@ -54,6 +54,7 @@ class ArrayNodeDefinitionTest extends TestCase
             array('defaultValue', array(array())),
             array('addDefaultChildrenIfNoneSet', array()),
             array('requiresAtLeastOneElement', array()),
+            array('cannotBeEmpty', array()),
             array('useAttributeAsKey', array('foo')),
         );
     }
@@ -285,6 +286,32 @@ class ArrayNodeDefinitionTest extends TestCase
         );
     }
 
+    public function testRequiresAtLeastOneElement()
+    {
+        $node = new ArrayNodeDefinition('root');
+        $node
+            ->requiresAtLeastOneElement()
+            ->integerPrototype();
+
+        $node->getNode()->finalize(array(1));
+
+        $this->addToAssertionCount(1);
+    }
+
+    /**
+     * @expectedException \Symfony\Component\Config\Definition\Exception\InvalidConfigurationException
+     * @expectedExceptionMessage The path "root" should have at least 1 element(s) defined.
+     */
+    public function testCannotBeEmpty()
+    {
+        $node = new ArrayNodeDefinition('root');
+        $node
+            ->cannotBeEmpty()
+            ->integerPrototype();
+
+        $node->getNode()->finalize(array());
+    }
+
     protected function getField($object, $field)
     {
         $reflection = new \ReflectionProperty($object, $field);