minor #29777 [VarDumper] Improve performance of AbstractCloner (javie…

…reguiluz)

This PR was merged into the 4.3-dev branch.

Discussion
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[VarDumper] Improve performance of AbstractCloner

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | no
| New feature?  | no <!-- don't forget to update src/**/CHANGELOG.md files -->
| BC breaks?    | no     <!-- see https://symfony.com/bc -->
| Deprecations? | no <!-- don't forget to update UPGRADE-*.md and src/**/CHANGELOG.md files -->
| Tests pass?   | yes    <!-- please add some, will be required by reviewers -->
| Fixed tickets | -   <!-- #-prefixed issue number(s), if any -->
| License       | MIT
| Doc PR        | -

While profiling Symfony in "dev" environment (see #29762) I found that `VarCloner::addCasters()` was making thousands of `strtolower()` calls.

![varcloner-addcasters](https://user-images.githubusercontent.com/73419/50694461-40a1bd80-103a-11e9-83c0-a28b8f8f161e.png)

In this PR I propose to remove all those calls. I think it's possible to do it ... but I could be completely wrong, so please review.

-----

As a side note, in the past we did the same `strtolower()` to service IDs and parameter names. We stopped doing that in Symfony 3.3 and it gave us a small performance improvement (same as we could gain here).

If the `strtolower()` calls of `VarCloner::addCasters()` are made just to apply the caster even if the class name is wrongly spelled, I think we could make this change. My guess is that nothing would break for the user (unlike removing the `strtolower()` in DependencyInjection, which broke wrongly spelled services and params). Thanks!

Commits
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cff23e5 [VarDumper] Improve performance of AbstractCloner

src/Symfony/Component/VarDumper/Cloner/AbstractCloner.php

@@ -69,7 +69,7 @@ abstract class AbstractCloner implements ClonerInterface
         'DOMProcessingInstruction' => ['Symfony\Component\VarDumper\Caster\DOMCaster', 'castProcessingInstruction'],
         'DOMXPath' => ['Symfony\Component\VarDumper\Caster\DOMCaster', 'castXPath'],
 
-        'XmlReader' => ['Symfony\Component\VarDumper\Caster\XmlReaderCaster', 'castXmlReader'],
+        'XMLReader' => ['Symfony\Component\VarDumper\Caster\XmlReaderCaster', 'castXmlReader'],
 
         'ErrorException' => ['Symfony\Component\VarDumper\Caster\ExceptionCaster', 'castErrorException'],
         'Exception' => ['Symfony\Component\VarDumper\Caster\ExceptionCaster', 'castException'],
@@ -177,7 +177,7 @@ public function __construct(array $casters = null)
     public function addCasters(array $casters)
     {
         foreach ($casters as $type => $callback) {
-            $closure = &$this->casters['' === $type || ':' === $type[0] ? $type : strtolower($type)][];
+            $closure = &$this->casters[$type][];
             $closure = $callback instanceof \Closure ? $callback : static function (...$args) use ($callback, &$closure) {
                 return ($closure = \Closure::fromCallable($callback))(...$args);
             };
@@ -282,15 +282,15 @@ protected function castObject(Stub $stub, $isNested)
             list($i, $parents, $hasDebugInfo) = $this->classInfo[$class];
         } else {
             $i = 2;
-            $parents = [strtolower($class)];
+            $parents = [$class];
             $hasDebugInfo = method_exists($class, '__debugInfo');
 
             foreach (class_parents($class) as $p) {
-                $parents[] = strtolower($p);
+                $parents[] = $p;
                 ++$i;
             }
             foreach (class_implements($class) as $p) {
-                $parents[] = strtolower($p);
+                $parents[] = $p;
                 ++$i;
             }
             $parents[] = '*';