Add handling for LibraryInstaller returning PromiseInterface

Author: Seldaek

src/Composer/Installers/Installer.php

@@ -9,6 +9,7 @@
 use Composer\Package\PackageInterface;
 use Composer\Repository\InstalledRepositoryInterface;
 use Composer\Util\Filesystem;
+use React\Promise\PromiseInterface;
 
 class Installer extends LibraryInstaller
 {
@@ -160,9 +161,21 @@ public function getInstallPath(PackageInterface $package)
 
     public function uninstall(InstalledRepositoryInterface $repo, PackageInterface $package)
     {
-        parent::uninstall($repo, $package);
         $installPath = $this->getPackageBasePath($package);
-        $this->io->write(sprintf('Deleting %s - %s', $installPath, !file_exists($installPath) ? '<comment>deleted</comment>' : '<error>not deleted</error>'));
+        $io = $this->io;
+        $outputStatus = function () use ($io, $installPath) {
+            $io->write(sprintf('Deleting %s - %s', $installPath, !file_exists($installPath) ? '<comment>deleted</comment>' : '<error>not deleted</error>'));
+        };
+
+        $promise = parent::uninstall($repo, $package);
+
+        // Composer v2 might return a promise here
+        if ($promise instanceof PromiseInterface) {
+            return $promise->then($outputStatus);
+        }
+
+        // If not, execute the code right away as parent::uninstall executed synchronously (composer v1, or v2 without async)
+        $outputStatus();
     }
 
     /**