feature #18359 [Form] [DoctrineBridge] optimized LazyChoiceList and DoctrineChoiceLoader (HeahDude)

This PR was merged into the 3.1-dev branch.

Discussion
----------

[Form] [DoctrineBridge] optimized LazyChoiceList and DoctrineChoiceLoader

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

Problem
======
Actually we got a circular dependency:

| Object | Return
|----------|-------------|
|`DefaultChoiceListFactory::createListFromLoader()` (decorated) | `LazyChoiceList` with loader and resolved `$value`
| `LazyChoiceList::get*` | `DoctrineChoiceLoader` with resolved `$value`
`DoctrineChoiceLoader::loadChoiceList()` | (decorated) `DefaultChoiceListFactory` with loaded choices and resolved `$value`
`DefaultChoiceListFactory::createListFromChoices()` | `ArrayChoiceList` with `resolved `$value`

With this refactoring, the `DoctrineChoiceLoader` is no longer dependant to the factory, the `ChoiceLoaderInterface::loadChoiceList()` must return a `ChoiceListInterface` but should not need a decorated factory while `$value` is already resolved. It should remain lazy IMHO.

Solution
======

| Object | Return |
|----------|-----------|
| `DefaultChoiceListFactory::createListFromLoader()` | `LazyChoiceList` with loader and resolved `$value`
| `LazyChoiceList::get*()` | `DoctrineChoiceLoader` with resolved `$value`
| `DoctrineChoiceLoader::loadChoiceList()` | `ArrayChoiceList` with resolved `$value`.

Since `choiceListFactory` is a private property, this change should be safe regarding BC.

To justify this change, I've made some blackfire profiling.
You can see my [branch of SE here](https://github.com/HeahDude/symfony-standard/tree/test/optimize-doctrine_choice_loader) and the [all in file test implementation](https://github.com/HeahDude/symfony-standard/blob/test/optimize-doctrine_choice_loader/src/AppBundle/Controller/DefaultController.php).

Basically it loads a form with 3 `EntityType` fields with different classes holding 50 instances each.

(INIT events are profiled with an empty cache)

When | What | Diff (SE => PR)
--------|-------|------
INIT (1) | build form (load types) | [see](https://blackfire.io/profiles/compare/061d5d28-15c6-4e01-b8c0-3edc9cb8daf0/graph)
INIT (2) | build view (load choices) | [see](https://blackfire.io/profiles/compare/04f142a8-d886-405a-be4d-636ba82d8acd/graph)
CACHED | build form (load types) | [see](https://blackfire.io/profiles/compare/293b27b6-aa58-42ae-bafb-655513201505/graph)
CACHED | build view (load choices) | [see](https://blackfire.io/profiles/compare/e5b37dfe-cc9e-498f-b98a-7448830ad190/graph)
SUBMIT | build form (load types) | [see](https://blackfire.io/profiles/compare/7f3baea9-0d27-46b6-8c24-c577742382dc/graph)
SUBMIT | handle request (load choices) | [see](https://blackfire.io/profiles/compare/8644ebfb-4397-495b-8f3d-1a6e1d7f8476/graph)
SUBMIT | build view (load values) | [see](https://blackfire.io/profiles/compare/89c3cc7c-ea07-4300-91b3-99004cb58ea1/graph)

(1):
![build_form-no_cache](https://cloud.githubusercontent.com/assets/10107633/14136166/b5a85eb8-f661-11e5-8556-3e0dcbfaf404.jpg)
(2):
![build_view-no_cache](https://cloud.githubusercontent.com/assets/10107633/14136240/1162f3ee-f662-11e5-834a-1ed1e519dc83.jpg)

It can seem like 1 and 2 balance each other but it comes clear when comparing values:

| -  | Build form | Build view |
|-----|---------|--------------|
| wall time | -88 ms | +9.71 ms
| blocking I/O | -40 ms | +3.67 ms
| cpu | -48 ms | +13.4 ms
| memory | -4.03 MB | +236 kB
| network | -203 B | +2.21 kB

Commits
-------

98621f4 [Form] optimized LazyChoiceList
86b2ff1 [DoctrineBridge] optimized DoctrineChoiceLoader

Author: fabpot

Form/ChoiceList/DoctrineChoiceLoader.php

@@ -12,6 +12,7 @@
 namespace Symfony\Bridge\Doctrine\Form\ChoiceList;
 
 use Doctrine\Common\Persistence\ObjectManager;
+use Symfony\Component\Form\ChoiceList\ArrayChoiceList;
 use Symfony\Component\Form\ChoiceList\ChoiceListInterface;
 use Symfony\Component\Form\ChoiceList\Factory\ChoiceListFactoryInterface;
 use Symfony\Component\Form\ChoiceList\Loader\ChoiceLoaderInterface;
@@ -60,20 +61,31 @@ class DoctrineChoiceLoader implements ChoiceLoaderInterface
      * passed which optimizes the object loading for one of the Doctrine
      * mapper implementations.
      *
-     * @param ChoiceListFactoryInterface $factory      The factory for creating
-     *                                                 the loaded choice list
      * @param ObjectManager              $manager      The object manager
      * @param string                     $class        The class name of the
      *                                                 loaded objects
      * @param IdReader                   $idReader     The reader for the object
      *                                                 IDs.
+     * @param ChoiceListFactoryInterface $factory      The factory for creating
+     *                                                 the loaded choice list
      * @param null|EntityLoaderInterface $objectLoader The objects loader
      */
-    public function __construct(ChoiceListFactoryInterface $factory, ObjectManager $manager, $class, IdReader $idReader = null, EntityLoaderInterface $objectLoader = null)
+    public function __construct($manager, $class, $idReader = null, $objectLoader = null, $factory = null)
     {
+        // BC to be removed and replace with type hints in 4.0
+        if ($manager instanceof ChoiceListFactoryInterface) {
+            @trigger_error(sprintf('Passing a ChoiceListFactoryInterface to %s is deprecated since version 3.1 and will no longer be supported in 4.0. You should either call "%s::loadChoiceList" or override it to return a ChoiceListInterface.', __CLASS__, __CLASS__));
+
+            // Provide a BC layer since $factory has changed
+            // form first to last argument as of 3.1
+            $this->factory = $manager;
+            $manager = $class;
+            $class = $idReader;
+            $objectLoader = $factory;
+        }
+
         $classMetadata = $manager->getClassMetadata($class);
 
-        $this->factory = $factory;
         $this->manager = $manager;
         $this->class = $classMetadata->getName();
         $this->idReader = $idReader ?: new IdReader($manager, $classMetadata);
@@ -93,9 +105,7 @@ public function loadChoiceList($value = null)
             ? $this->objectLoader->getEntities()
             : $this->manager->getRepository($this->class)->findAll();
 
-        $this->choiceList = $this->factory->createListFromChoices($objects, $value);
-
-        return $this->choiceList;
+        return $this->choiceList = new ArrayChoiceList($objects, $value);
     }
 
     /**
@@ -146,7 +156,7 @@ public function loadChoicesForValues(array $values, $value = null)
 
         // Optimize performance in case we have an object loader and
         // a single-field identifier
-        $optimize = null === $value || is_array($value) && $value[0] === $this->idReader;
+        $optimize = null === $value || is_array($value) && $this->idReader === $value[0];
 
         if ($optimize && !$this->choiceList && $this->objectLoader && $this->idReader->isSingleId()) {
             $unorderedObjects = $this->objectLoader->getEntitiesByIds($this->idReader->getIdField(), $values);

Form/Type/DoctrineType.php

@@ -160,7 +160,6 @@ public function configureOptions(OptionsResolver $resolver)
                 }
 
                 $doctrineChoiceLoader = new DoctrineChoiceLoader(
-                    $this->choiceListFactory,
                     $options['em'],
                     $options['class'],
                     $options['id_reader'],