Issue #2579663 by Mile23, webflo, joshtaylor: Can't use 'composer install'...

Issue #2579663 by Mile23, webflo, joshtaylor: Can't use 'composer install' with missing composer.lock and vendor folder

core/lib/Drupal/Core/Composer/Composer.php

@@ -10,6 +10,7 @@
 use Drupal\Component\PhpStorage\FileStorage;
 use Composer\Script\Event;
 use Composer\Installer\PackageEvent;
+use Composer\Semver\Constraint\Constraint;
 
 /**
  * Provides static functions for composer script events.
@@ -71,11 +72,19 @@ class Composer {
   ];
 
   /**
-   * Add vendor classes to composers static classmap.
+   * Add vendor classes to Composer's static classmap.
    */
   public static function preAutoloadDump(Event $event) {
-    $composer = $event->getComposer();
-    $package = $composer->getPackage();
+    // We need the root package so we can add our classmaps to its loader.
+    $package = $event->getComposer()->getPackage();
+    // We need the local repository so that we can query and see if it's likely
+    // that our files are present there.
+    $repository = $event->getComposer()->getRepositoryManager()->getLocalRepository();
+    // This is, essentially, a null constraint. We only care whether the package
+    // is present in vendor/ yet, but findPackage() requires it.
+    $constraint = new Constraint('>', '');
+    // Check for our packages, and then optimize them if they're present.
+    if ($repository->findPackage('symfony/http-foundation', $constraint)) {
       $autoload = $package->getAutoload();
       $autoload['classmap'] = array_merge($autoload['classmap'], array(
         'vendor/symfony/http-foundation/Request.php',
@@ -83,12 +92,19 @@ public static function preAutoloadDump(Event $event) {
         'vendor/symfony/http-foundation/FileBag.php',
         'vendor/symfony/http-foundation/ServerBag.php',
         'vendor/symfony/http-foundation/HeaderBag.php',
+      ));
+      $package->setAutoload($autoload);
+    }
+    if ($repository->findPackage('symfony/http-kernel', $constraint)) {
+      $autoload = $package->getAutoload();
+      $autoload['classmap'] = array_merge($autoload['classmap'], array(
         'vendor/symfony/http-kernel/HttpKernel.php',
         'vendor/symfony/http-kernel/HttpKernelInterface.php',
         'vendor/symfony/http-kernel/TerminableInterface.php',
       ));
       $package->setAutoload($autoload);
     }
+  }
 
   /**
    * Ensures that .htaccess and web.config files are present in Composer root.