[Bug] Query Cache mangled if saved by-reference (doctrine#6552)

Bug emerged in
doctrine#6510 (comment)

The current implementation of query cache relies on the cache **not**
saved by-reference; the bug has never been seen before because by
default `new ArrayAdapter()` saves the cache with serialization, hence
breaking the by-reference pointer.

Once the _by-reference_ tecnique is used, two issues pop up:

1. `\Doctrine\DBAL\Cache\ArrayResult::$num` is never reset, so once it
gets incremented in the first `\Doctrine\DBAL\Cache\ArrayResult::fetch`
call, the following calls will always fail
2. Even considering fixing the `$num` property reset, a manual call on
`\Doctrine\DBAL\Result::free` will by cascade call the
`\Doctrine\DBAL\Cache\ArrayResult::free` method erasing all the saved
results

I think that the `ArrayResult` implementation is not the culprit, but
rather the doctrine#6510 giving to the cache backend the internal object by
reference instead of giving it a copy.

src/Connection.php

@@ -811,7 +811,7 @@ public function executeCacheQuery(string $sql, array $params, array $types, Quer
             }
 
             if (isset($value[$realKey]) && $value[$realKey] instanceof ArrayResult) {
-                return new Result($value[$realKey], $this);
+                return new Result(clone $value[$realKey], $this);
             }
         } else {
             $value = [];
@@ -837,7 +837,7 @@ public function executeCacheQuery(string $sql, array $params, array $types, Quer
 
         $resultCache->save($item);
 
-        return new Result($value[$realKey], $this);
+        return new Result(clone $value[$realKey], $this);
     }
 
     /**

tests/Connection/CachedQueryTest.php

@@ -8,49 +8,60 @@
 use Doctrine\DBAL\Cache\QueryCacheProfile;
 use Doctrine\DBAL\Connection;
 use Doctrine\DBAL\Driver;
+use PHPUnit\Framework\Attributes\DataProvider;
 use PHPUnit\Framework\TestCase;
+use Psr\Cache\CacheItemPoolInterface;
 use Symfony\Component\Cache\Adapter\ArrayAdapter;
 
 class CachedQueryTest extends TestCase
 {
-    public function testCachedQuery(): void
+    #[DataProvider('providePsrCacheImplementations')]
+    public function testCachedQuery(callable $psrCacheProvider): void
     {
-        $cache = new ArrayAdapter();
+        $cache = $psrCacheProvider();
 
         $connection = $this->createConnection(1, ['foo'], [['bar']]);
         $qcp        = new QueryCacheProfile(0, __FUNCTION__, $cache);
 
-        self::assertSame([['foo' => 'bar']], $connection->executeCacheQuery('SELECT 1', [], [], $qcp)
+        $firstResult = $connection->executeCacheQuery('SELECT 1', [], [], $qcp);
+        self::assertSame([['foo' => 'bar']], $firstResult
+            ->fetchAllAssociative());
+        $firstResult->free();
+        $secondResult = $connection->executeCacheQuery('SELECT 1', [], [], $qcp);
+        self::assertSame([['foo' => 'bar']], $secondResult
             ->fetchAllAssociative());
+        $secondResult->free();
         self::assertSame([['foo' => 'bar']], $connection->executeCacheQuery('SELECT 1', [], [], $qcp)
             ->fetchAllAssociative());
 
         self::assertCount(1, $cache->getItem(__FUNCTION__)->get());
     }
 
-    public function testCachedQueryWithChangedImplementationIsExecutedTwice(): void
+    #[DataProvider('providePsrCacheImplementations')]
+    public function testCachedQueryWithChangedImplementationIsExecutedTwice(callable $psrCacheProvider): void
     {
         $connection = $this->createConnection(2, ['baz'], [['qux']]);
 
         self::assertSame([['baz' => 'qux']], $connection->executeCacheQuery(
             'SELECT 1',
             [],
             [],
-            new QueryCacheProfile(0, __FUNCTION__, new ArrayAdapter()),
+            new QueryCacheProfile(0, __FUNCTION__, $psrCacheProvider()),
         )->fetchAllAssociative());
 
         self::assertSame([['baz' => 'qux']], $connection->executeCacheQuery(
             'SELECT 1',
             [],
             [],
-            new QueryCacheProfile(0, __FUNCTION__, new ArrayAdapter()),
+            new QueryCacheProfile(0, __FUNCTION__, $psrCacheProvider()),
         )->fetchAllAssociative());
     }
 
-    public function testOldCacheFormat(): void
+    #[DataProvider('providePsrCacheImplementations')]
+    public function testOldCacheFormat(callable $psrCacheProvider): void
     {
         $connection = $this->createConnection(1, ['foo'], [['bar']]);
-        $cache      = new ArrayAdapter();
+        $cache      = $psrCacheProvider();
         $qcp        = new QueryCacheProfile(0, __FUNCTION__, $cache);
 
         [$cacheKey, $realKey] = $qcp->generateCacheKeys('SELECT 1', [], [], []);
@@ -83,4 +94,13 @@ private function createConnection(int $expectedQueryCount, array $columnNames, a
 
         return new Connection([], $driver);
     }
+
+    /** @return array<non-empty-string, list<callable():CacheItemPoolInterface>> */
+    public static function providePsrCacheImplementations(): array
+    {
+        return [
+            'serialized' => [static fn () => new ArrayAdapter(0, true)],
+            'by-reference' => [static fn () => new ArrayAdapter(0, false)],
+        ];
+    }
 }