[Cache] fix using ProxyAdapter inside TagAwareAdapter

src/Symfony/Component/Cache/Adapter/ProxyAdapter.php

@@ -45,12 +45,15 @@ public function __construct(CacheItemPoolInterface $pool, $namespace = '', $defa
             function ($key, $innerItem) use ($defaultLifetime, $poolHash) {
                 $item = new CacheItem();
                 $item->key = $key;
-                $item->value = $innerItem->get();
-                $item->isHit = $innerItem->isHit();
                 $item->defaultLifetime = $defaultLifetime;
-                $item->innerItem = $innerItem;
                 $item->poolHash = $poolHash;
-                $innerItem->set(null);
+
+                if (null !== $innerItem) {
+                    $item->value = $innerItem->get();
+                    $item->isHit = $innerItem->isHit();
+                    $item->innerItem = $innerItem;
+                    $innerItem->set(null);
+                }
 
                 return $item;
             },
@@ -156,7 +159,18 @@ private function doSave(CacheItemInterface $item, $method)
         if (null === $expiry && 0 < $item["\0*\0defaultLifetime"]) {
             $expiry = time() + $item["\0*\0defaultLifetime"];
         }
-        $innerItem = $item["\0*\0poolHash"] === $this->poolHash ? $item["\0*\0innerItem"] : $this->pool->getItem($this->namespace.$item["\0*\0key"]);
+
+        if ($item["\0*\0poolHash"] === $this->poolHash && $item["\0*\0innerItem"]) {
+            $innerItem = $item["\0*\0innerItem"];
+        } elseif ($this->pool instanceof AdapterInterface) {
+            // this is an optimization specific for AdapterInterface implementations
+            // so we can save a round-trip to the backend by just creating a new item
+            $f = $this->createCacheItem;
+            $innerItem = $f($this->namespace.$item["\0*\0key"], null);
+        } else {
+            $innerItem = $this->pool->getItem($this->namespace.$item["\0*\0key"]);
+        }
+
         $innerItem->set($item["\0*\0value"]);
         $innerItem->expiresAt(null !== $expiry ? \DateTime::createFromFormat('U', $expiry) : null);
 

src/Symfony/Component/Cache/Adapter/TagAwareAdapter.php

@@ -48,7 +48,6 @@ function ($key, $value, CacheItem $protoItem) {
                 $item->value = $value;
                 $item->defaultLifetime = $protoItem->defaultLifetime;
                 $item->expiry = $protoItem->expiry;
-                $item->innerItem = $protoItem->innerItem;
                 $item->poolHash = $protoItem->poolHash;
 
                 return $item;

src/Symfony/Component/Cache/Tests/Adapter/TagAwareAndProxyAdapterIntegrationTest.php

@@ -0,0 +1,38 @@
+<?php
+
+namespace Symfony\Component\Cache\Tests\Adapter;
+
+use PHPUnit\Framework\TestCase;
+use Psr\Cache\CacheItemPoolInterface;
+use Symfony\Component\Cache\Adapter\ArrayAdapter;
+use Symfony\Component\Cache\Adapter\ProxyAdapter;
+use Symfony\Component\Cache\Adapter\TagAwareAdapter;
+use Symfony\Component\Cache\Tests\Fixtures\ExternalAdapter;
+
+class TagAwareAndProxyAdapterIntegrationTest extends TestCase
+{
+    /**
+     * @dataProvider dataProvider
+     */
+    public function testIntegrationUsingProxiedAdapter(CacheItemPoolInterface $proxiedAdapter)
+    {
+        $cache = new TagAwareAdapter(new ProxyAdapter($proxiedAdapter));
+
+        $item = $cache->getItem('foo');
+        $item->tag(['tag1', 'tag2']);
+        $item->set('bar');
+        $cache->save($item);
+
+        $this->assertSame('bar', $cache->getItem('foo')->get());
+    }
+
+    public function dataProvider()
+    {
+        return [
+            [new ArrayAdapter()],
+            // also testing with a non-AdapterInterface implementation
+            // because the ProxyAdapter behaves slightly different for those
+            [new ExternalAdapter()],
+        ];
+    }
+}