Add source package name to debug info when enabling plugins

src/Composer/Plugin/PluginManager.php

@@ -229,7 +229,7 @@ class PluginManager
                 $this->registeredPlugins[$package->getName()] = $installer;
             } elseif (class_exists($class)) {
                 $plugin = new $class();
-                $this->addPlugin($plugin, $isGlobalPlugin);
+                $this->addPlugin($plugin, $isGlobalPlugin, $package);
                 $this->registeredPlugins[$package->getName()] = $plugin;
             } elseif ($failOnMissingClasses) {
                 throw new \UnexpectedValueException('Plugin '.$package->getName().' could not be initialized, class not found: '.$class);
@@ -319,11 +319,19 @@ class PluginManager
      * programmatically and want to register a plugin class directly this is a valid way
      * to do it.
      *
-     * @param PluginInterface $plugin plugin instance
+     * @param PluginInterface   $plugin        plugin instance
+     * @param ?PackageInterface $sourcePackage Package from which the plugin comes from
      */
-    public function addPlugin(PluginInterface $plugin, $isGlobalPlugin = false)
+    public function addPlugin(PluginInterface $plugin, $isGlobalPlugin = false, PackageInterface $sourcePackage = null)
     {
-        $this->io->writeError('Loading plugin '.get_class($plugin).($isGlobalPlugin ? ' (installed globally)' : ''), true, IOInterface::DEBUG);
+        $details = array();
+        if ($sourcePackage) {
+            $details[] = 'from '.$sourcePackage->getName();
+        }
+        if ($isGlobalPlugin) {
+            $details[] = 'installed globally';
+        }
+        $this->io->writeError('Loading plugin '.get_class($plugin).($details ? ' ('.implode(', ', $details).')' : ''), true, IOInterface::DEBUG);
         $this->plugins[] = $plugin;
         $plugin->activate($this->composer, $this->io);