Fix for #18843

src/Symfony/Component/Yaml/Dumper.php

@@ -58,7 +58,7 @@ class Dumper
         if ($inline <= 0 || !is_array($input) || empty($input)) {
             $output .= $prefix.Inline::dump($input, $exceptionOnInvalidType, $objectSupport);
         } else {
-            $isAHash = array_keys($input) !== range(0, count($input) - 1);
+            $isAHash = Inline::isHash($input);
 
             foreach ($input as $key => $value) {
                 $willBeInlined = $inline - 1 <= 0 || !is_array($value) || empty($value);

src/Symfony/Component/Yaml/Inline.php

@@ -145,6 +145,28 @@ class Inline
         }
     }
 
+    /**
+     * Check if given array is hash or just normal indexed array.
+     *
+     * @internal
+     *
+     * @param array $value The PHP array to check
+     *
+     * @return bool true if value is hash array, false otherwise
+     */
+    public static function isHash(array $value)
+    {
+        $expectedKey = 0;
+
+        foreach ($value as $key => $val) {
+            if ($key !== $expectedKey++) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
     /**
      * Dumps a PHP array to a YAML string.
      *
@@ -157,11 +179,7 @@ class Inline
     private static function dumpArray($value, $exceptionOnInvalidType, $objectSupport)
     {
         // array
-        $keys = array_keys($value);
-        $keysCount = count($keys);
-        if ((1 === $keysCount && '0' == $keys[0])
-            || ($keysCount > 1 && array_reduce($keys, function ($v, $w) { return (int) $v + $w; }, 0) === $keysCount * ($keysCount - 1) / 2)
-        ) {
+        if ($value && !self::isHash($value)) {
             $output = array();
             foreach ($value as $val) {
                 $output[] = self::dump($val, $exceptionOnInvalidType, $objectSupport);
@@ -170,7 +188,7 @@ class Inline
             return sprintf('[%s]', implode(', ', $output));
         }
 
-        // mapping
+        // hash
         $output = array();
         foreach ($value as $key => $val) {
             $output[] = sprintf('%s: %s', self::dump($key, $exceptionOnInvalidType, $objectSupport), self::dump($val, $exceptionOnInvalidType, $objectSupport));

src/Symfony/Component/Yaml/Tests/InlineTest.php

@@ -169,6 +169,24 @@ class InlineTest extends \PHPUnit_Framework_TestCase
         Inline::parse('{ foo: * #foo }');
     }
 
+    /**
+     * @dataProvider getDataForIsHash
+     */
+    public function testIsHash($array, $expected)
+    {
+        $this->assertSame($expected, Inline::isHash($array));
+    }
+
+    public function getDataForIsHash()
+    {
+        return array(
+            array(array(), false),
+            array(array(1, 2, 3), false),
+            array(array(2 => 1, 1 => 2, 0 => 3), true),
+            array(array('foo' => 1, 'bar' => 2), true),
+        );
+    }
+
     protected function getTestsForParse()
     {
         return array(
@@ -296,6 +314,8 @@ class InlineTest extends \PHPUnit_Framework_TestCase
             '[foo, { bar: foo, foo: [foo, { bar: foo }] }, [foo, { bar: foo }]]' => array('foo', array('bar' => 'foo', 'foo' => array('foo', array('bar' => 'foo'))), array('foo', array('bar' => 'foo'))),
 
             '[foo, \'@foo.baz\', { \'%foo%\': \'foo is %foo%\', bar: \'%foo%\' }, true, \'@service_container\']' => array('foo', '@foo.baz', array('%foo%' => 'foo is %foo%', 'bar' => '%foo%'), true, '@service_container'),
+
+            '{ foo: { bar: { 1: 2, baz: 3 } } }' => array('foo' => array('bar' => array(1 => 2, 'baz' => 3))),
         );
     }
 }