minor #32188 [PropertyInfo] add static cache to ContextFactory (bastnic)

This PR was merged into the 4.4 branch.

Discussion
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[PropertyInfo] add static cache to ContextFactory

| Q             | A
| ------------- | ---
| Branch?       | 4.4
| Bug fix?      | no (performance...)
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #32073, api-platform/api-platform#1159
| License       | MIT
| Doc PR        | no

The issue is very very well described here #32073, and was also discussed a few weeks ago with @dunglas here api-platform/api-platform#1159.

`ContextFactory::createFromReflector` is heavy, and it's called redundanlty
by `Symfony\Component\PropertyInfo\Extractor\PhpDocExtractor` for each property
and methods. Avoid that by parsing it only once and then use static cache

This is a quite big performance problem.

![Deepin Capture-écran_zone de sélection _20190626142041](https://user-images.githubusercontent.com/84887/60179692-8471c480-981e-11e9-9e3c-3f9c0b83b01b.png)

Commits
-------

063e880 [PropertyInfo] add static cache to ContextFactory

src/Symfony/Component/PropertyInfo/Extractor/PhpDocExtractor.php

@@ -14,6 +14,7 @@
 use phpDocumentor\Reflection\DocBlock;
 use phpDocumentor\Reflection\DocBlockFactory;
 use phpDocumentor\Reflection\DocBlockFactoryInterface;
+use phpDocumentor\Reflection\Types\Context;
 use phpDocumentor\Reflection\Types\ContextFactory;
 use Symfony\Component\PropertyInfo\PropertyDescriptionExtractorInterface;
 use Symfony\Component\PropertyInfo\PropertyTypeExtractorInterface;
@@ -38,6 +39,11 @@ class PhpDocExtractor implements PropertyDescriptionExtractorInterface, Property
      */
     private $docBlocks = [];
 
+    /**
+     * @var Context[]
+     */
+    private $contexts = [];
+
     private $docBlockFactory;
     private $contextFactory;
     private $phpDocTypeHelper;
@@ -191,7 +197,7 @@ private function getDocBlockFromProperty(string $class, string $property): ?DocB
         }
 
         try {
-            return $this->docBlockFactory->create($reflectionProperty, $this->contextFactory->createFromReflector($reflectionProperty->getDeclaringClass()));
+            return $this->docBlockFactory->create($reflectionProperty, $this->createFromReflector($reflectionProperty->getDeclaringClass()));
         } catch (\InvalidArgumentException $e) {
             return null;
         }
@@ -227,9 +233,25 @@ private function getDocBlockFromMethod(string $class, string $ucFirstProperty, i
         }
 
         try {
-            return [$this->docBlockFactory->create($reflectionMethod, $this->contextFactory->createFromReflector($reflectionMethod)), $prefix];
+            return [$this->docBlockFactory->create($reflectionMethod, $this->createFromReflector($reflectionMethod->getDeclaringClass())), $prefix];
         } catch (\InvalidArgumentException $e) {
             return null;
         }
     }
+
+    /**
+     * Prevents a lot of redundant calls to ContextFactory::createForNamespace().
+     */
+    private function createFromReflector(\ReflectionClass $reflector): Context
+    {
+        $cacheKey = $reflector->getNamespaceName().':'.$reflector->getFileName();
+
+        if (isset($this->contexts[$cacheKey])) {
+            return $this->contexts[$cacheKey];
+        }
+
+        $this->contexts[$cacheKey] = $this->contextFactory->createFromReflector($reflector);
+
+        return $this->contexts[$cacheKey];
+    }
 }