Activate APCu on PHP 7

Fix an issue with APCus inc and dec methods on PHP 7

see https://github.com/krakjoe/apcu/issues/183#issuecomment-244038221 for details

.drone.yml

@@ -10,7 +10,7 @@ build:
       - git submodule update --init
       - NOCOVERAGE=true TEST_SELECTION=NODB ./autotest.sh sqlite
   nodb-php7.0:
-    image: nextcloudci/php7.0:1.0.9
+    image: nextcloudci/php7.0:php7.0-1
     commands:
       - rm -rf data/* config/config.php # TODO: remove this - temporary fix for CI issues
       - git submodule update --init

lib/private/Memcache/APCu.php

@@ -88,7 +88,21 @@ class APCu extends Cache implements IMemcache {
 	 */
 	public function inc($key, $step = 1) {
 		$this->add($key, 0);
-		return apcu_inc($this->getPrefix() . $key, $step);
+		/**
+		 * TODO - hack around a PHP 7 specific issue in APCu
+		 *
+		 * on PHP 7 the apcu_inc method on a non-existing object will increment
+		 * "0" and result in "1" as value - therefore we check for existence
+		 * first
+		 *
+		 * on PHP 5.6 this is not the case
+		 *
+		 * see https://github.com/krakjoe/apcu/issues/183#issuecomment-244038221
+		 * for details
+		 */
+		return apcu_exists($this->getPrefix() . $key)
+			? apcu_inc($this->getPrefix() . $key, $step)
+			: false;
 	}
 
 	/**
@@ -99,7 +113,21 @@ class APCu extends Cache implements IMemcache {
 	 * @return int | bool
 	 */
 	public function dec($key, $step = 1) {
-		return apcu_dec($this->getPrefix() . $key, $step);
+		/**
+		 * TODO - hack around a PHP 7 specific issue in APCu
+		 *
+		 * on PHP 7 the apcu_dec method on a non-existing object will decrement
+		 * "0" and result in "-1" as value - therefore we check for existence
+		 * first
+		 *
+		 * on PHP 5.6 this is not the case
+		 *
+		 * see https://github.com/krakjoe/apcu/issues/183#issuecomment-244038221
+		 * for details
+		 */
+		return apcu_exists($this->getPrefix() . $key)
+			? apcu_dec($this->getPrefix() . $key, $step)
+			: false;
 	}
 
 	/**