Fix handling of metapackages with null paths, and handling of paths which do not have a shortest-path and require an absolute path to be addressed

tests/Composer/Test/Repository/FilesystemRepositoryTest.php

@@ -12,6 +12,7 @@
 
 namespace Composer\Test\Repository;
 
+use Composer\Package\RootPackageInterface;
 use Composer\Repository\FilesystemRepository;
 use Composer\Test\TestCase;
 use Composer\Json\JsonFile;
@@ -157,12 +158,34 @@ class FilesystemRepositoryTest extends TestCase
         $pkg = $this->getPackage('c/c', '3.0');
         $repository->addPackage($pkg);
 
+        $pkg = $this->getPackage('meta/package', '3.0');
+        $pkg->setType('metapackage');
+        $repository->addPackage($pkg);
+
         $im = $this->getMockBuilder('Composer\Installer\InstallationManager')
             ->disableOriginalConstructor()
             ->getMock();
         $im->expects($this->any())
             ->method('getInstallPath')
-            ->will($this->returnValue('/foo/bar/vendor/woop/woop'));
+            ->will($this->returnCallback(function ($package) use ($dir) {
+                // check for empty paths handling
+                if ($package->getType() === 'metapackage') {
+                    return '';
+                }
+
+                if ($package->getName() === 'c/c') {
+                    // check for absolute paths
+                    return '/foo/bar/vendor/c/c';
+                }
+
+                // check for cwd
+                if ($package instanceof RootPackageInterface) {
+                    return $dir;
+                }
+
+                // check for relative paths
+                return 'vendor/'.$package->getName();
+            }));
 
         $repository->write(true, $im);
         $this->assertSame(require __DIR__.'/Fixtures/installed.php', require $dir.'/installed.php');