Add plugin-api-version used to generate a lock file in itself

src/Composer/Package/Locker.php

@@ -19,6 +19,7 @@ use Composer\Util\ProcessExecutor;
 use Composer\Repository\ArrayRepository;
 use Composer\Package\Dumper\ArrayDumper;
 use Composer\Package\Loader\ArrayLoader;
+use Composer\Plugin\PluginInterface;
 use Composer\Util\Git as GitUtil;
 use Composer\IO\IOInterface;
 use Seld\JsonLint\ParsingException;
@@ -322,6 +323,7 @@ class Locker
         if ($platformOverrides) {
             $lock['platform-overrides'] = $platformOverrides;
         }
+        $lock['plugin-api-version'] = PluginInterface::PLUGIN_API_VERSION;
 
         if (empty($lock['packages']) && empty($lock['packages-dev']) && empty($lock['platform']) && empty($lock['platform-dev'])) {
             if ($this->lockFile->exists()) {

tests/Composer/Test/InstallerTest.php

@@ -262,6 +262,7 @@ class InstallerTest extends TestCase
             unset($actualLock['hash']);
             unset($actualLock['content-hash']);
             unset($actualLock['_readme']);
+            unset($actualLock['plugin-api-version']);
             $this->assertEquals($expectLock, $actualLock);
         }
 

tests/Composer/Test/Package/LockerTest.php

@@ -13,6 +13,7 @@
 namespace Composer\Test\Package;
 
 use Composer\Package\Locker;
+use Composer\Plugin\PluginInterface;
 use Composer\IO\NullIO;
 use Composer\Test\TestCase;
 
@@ -154,6 +155,7 @@ class LockerTest extends TestCase
                 'platform-overrides' => array('foo/bar' => '1.0'),
                 'prefer-stable' => false,
                 'prefer-lowest' => false,
+                'plugin-api-version' => PluginInterface::PLUGIN_API_VERSION,
             ));
 
         $locker->setLockData(array($package1, $package2), array(), array(), array(), array(), 'dev', array(), false, false, array('foo/bar' => '1.0'));