bug #22981 [DependencyInjection] Fix named args support in ChildDefinition (dunglas)

This PR was squashed before being merged into the 3.3 branch (closes #22981).

Discussion
----------

[DependencyInjection] Fix named args support in ChildDefinition

| Q             | A
| ------------- | ---
| Branch?       | 3.3
| Bug fix?      | yes
| New feature?  | no <!-- don't forget updating src/**/CHANGELOG.md files -->
| BC breaks?    | no
| Deprecations? | no <!-- don't forget updating UPGRADE-*.md files -->
| Tests pass?   | yes
| Fixed tickets | n/a
| License       | MIT
| Doc PR        | n/a

Following @Tobion's review of #21383.

Commits
-------

1ab3e413d4 [DependencyInjection] Fix named args support in ChildDefinition

Author: fabpot

ChildDefinition.php

@@ -62,7 +62,7 @@ public function setParent($parent)
      * If replaceArgument() has been used to replace an argument, this method
      * will return the replacement value.
      *
-     * @param int $index
+     * @param int|string $index
      *
      * @return mixed The argument value
      *
@@ -74,13 +74,7 @@ public function getArgument($index)
             return $this->arguments['index_'.$index];
         }
 
-        $lastIndex = count(array_filter(array_keys($this->arguments), 'is_int')) - 1;
-
-        if ($index < 0 || $index > $lastIndex) {
-            throw new OutOfBoundsException(sprintf('The index "%d" is not in the range [0, %d].', $index, $lastIndex));
-        }
-
-        return $this->arguments[$index];
+        return parent::getArgument($index);
     }
 
     /**
@@ -91,8 +85,8 @@ public function getArgument($index)
      * certain conventions when you want to overwrite the arguments of the
      * parent definition, otherwise your arguments will only be appended.
      *
-     * @param int   $index
-     * @param mixed $value
+     * @param int|string $index
+     * @param mixed      $value
      *
      * @return self the current instance
      *
@@ -105,7 +99,7 @@ public function replaceArgument($index, $value)
         } elseif (0 === strpos($index, '$')) {
             $this->arguments[$index] = $value;
         } else {
-            throw new InvalidArgumentException('$index must be an integer.');
+            throw new InvalidArgumentException('The argument must be an existing index or the name of a constructor\'s parameter.');
         }
 
         return $this;

Tests/ChildDefinitionTest.php

@@ -113,6 +113,10 @@ public function testReplaceArgument()
         $this->assertSame('baz', $def->getArgument(1));
 
         $this->assertSame(array(0 => 'foo', 1 => 'bar', 'index_1' => 'baz'), $def->getArguments());
+
+        $this->assertSame($def, $def->replaceArgument('$bar', 'val'));
+        $this->assertSame('val', $def->getArgument('$bar'));
+        $this->assertSame(array(0 => 'foo', 1 => 'bar', 'index_1' => 'baz', '$bar' => 'val'), $def->getArguments());
     }
 
     /**