bug #14395 [Validator] Property paths starting with 0 are broken. (fago)

This PR was squashed before being merged into the 2.7 branch (closes #14395).

Discussion
----------

[Validator] Property paths starting with 0 are broken.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #14394
| License       | MIT
| Doc PR        | -

Commits
-------

1ced8da [Validator] Property paths starting with 0 are broken.

src/Symfony/Component/Validator/Tests/Util/PropertyPathTest.php

@@ -30,6 +30,7 @@ class PropertyPathTest extends \PHPUnit_Framework_TestCase
             array('', 'bar', 'bar', 'It returns the subPath if basePath is empty'),
             array('foo', 'bar', 'foo.bar', 'It append the subPath to the basePath'),
             array('foo', '[bar]', 'foo[bar]', 'It does not include the dot separator if subPath uses the array notation'),
+            array('0', 'bar', '0.bar', 'Leading zeros are kept.'),
         );
     }
 }

src/Symfony/Component/Validator/Util/PropertyPath.php

@@ -17,6 +17,7 @@ namespace Symfony\Component\Validator\Util;
  * For more extensive functionality, use Symfony's PropertyAccess component.
  *
  * @since  2.5
+ *
  * @author Bernhard Schussek <bschussek@gmail.com>
  */
 class PropertyPath
@@ -42,7 +43,7 @@ class PropertyPath
                 return $basePath.$subPath;
             }
 
-            return $basePath ? $basePath.'.'.$subPath : $subPath;
+            return '' !== (string) $basePath ? $basePath.'.'.$subPath : $subPath;
         }
 
         return $basePath;

src/Symfony/Component/Validator/Validator/RecursiveContextualValidator.php

@@ -34,6 +34,7 @@ use Symfony\Component\Validator\Util\PropertyPath;
  * Recursive implementation of {@link ContextualValidatorInterface}.
  *
  * @since  2.5
+ *
  * @author Bernhard Schussek <bschussek@gmail.com>
  */
 class RecursiveContextualValidator implements ContextualValidatorInterface
@@ -526,7 +527,7 @@ class RecursiveContextualValidator implements ContextualValidatorInterface
                 } elseif ($metadata->isGroupSequenceProvider()) {
                     // The group sequence is dynamically obtained from the validated
                     // object
-                    /** @var \Symfony\Component\Validator\GroupSequenceProviderInterface $object */
+                    /* @var \Symfony\Component\Validator\GroupSequenceProviderInterface $object */
                     $group = $object->getGroupSequence();
                     $defaultOverridden = true;
 
@@ -590,9 +591,7 @@ class RecursiveContextualValidator implements ContextualValidatorInterface
                     $object,
                     $cacheKey.':'.$propertyName,
                     $propertyMetadata,
-                    $propertyPath
-                        ? $propertyPath.'.'.$propertyName
-                        : $propertyName,
+                    PropertyPath::append($propertyPath, $propertyName),
                     $groups,
                     $cascadedGroups,
                     TraversalStrategy::IMPLICIT,