From 4bd748b4630d01e3c268a941f748d0c317b7a156 Mon Sep 17 00:00:00 2001
From: Jordi Boggiano <j.boggiano@seld.be>
Date: Sat, 19 Jul 2014 19:43:59 +0200
Subject: [PATCH] Fix BC issue from #3101

---
 src/Composer/Installer.php      | 12 +++++++++++-
 src/Composer/Package/Locker.php |  3 ++-
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/src/Composer/Installer.php b/src/Composer/Installer.php
index eb4db08c4..0fb66553b 100644
--- a/src/Composer/Installer.php
+++ b/src/Composer/Installer.php
@@ -648,7 +648,17 @@ class Installer
 
     private function createPolicy()
     {
-        return new DefaultPolicy((!$this->update && $this->locker->isLocked()) ? $this->locker->getPreferStable() : $this->package->getPreferStable());
+        $preferStable = null;
+        if (!$this->update && $this->locker->isLocked()) {
+            $preferStable = $this->locker->getPreferStable();
+        }
+        // old lock file without prefer stable will return null
+        // so in this case we use the composer.json info
+        if (null === $preferStable) {
+            $preferStable = $this->package->getPreferStable();
+        }
+
+        return new DefaultPolicy($preferStable);
     }
 
     private function createRequest(Pool $pool, RootPackageInterface $rootPackage, PlatformRepository $platformRepo)
diff --git a/src/Composer/Package/Locker.php b/src/Composer/Package/Locker.php
index bee955288..ab5d432e0 100644
--- a/src/Composer/Package/Locker.php
+++ b/src/Composer/Package/Locker.php
@@ -177,7 +177,7 @@ class Locker
     {
         $lockData = $this->getLockData();
 
-        return isset($lockData['prefer-stable']) ? $lockData['prefer-stable'] : false;
+        return isset($lockData['prefer-stable']) ? $lockData['prefer-stable'] : null;
     }
 
     public function getAliases()
@@ -210,6 +210,7 @@ class Locker
      * @param array  $aliases          array of aliases
      * @param string $minimumStability
      * @param array  $stabilityFlags
+     * @param bool   $preferStable
      *
      * @return bool
      */