Alternative implementation for Unknown command suggestions

alternative implementation for #12661, proof of concept, does not
include filtering by similarity yet.

issue #12659

framework/console/UnknownCommandException.php

@@ -0,0 +1,81 @@
+<?php
+/**
+ * @link http://www.yiiframework.com/
+ * @copyright Copyright (c) 2008 Yii Software LLC
+ * @license http://www.yiiframework.com/license/
+ */
+
+namespace yii\console;
+use yii\console\controllers\HelpController;
+
+/**
+ * Exception represents an exception caused by incorrect usage of a console command.
+ *
+ * @author Carsten Brandt <mail@cebe.cc>
+ * @since 2.0.11
+ */
+class UnknownCommandException extends Exception
+{
+    public $command;
+    /**
+     * @var Application
+     */
+    public $application;
+
+    public function __construct($route, $application, $code = 0, \Exception $previous = null)
+    {
+        $this->command = $route;
+        $this->application = $application;
+        parent::__construct("Unknown command \"$route\".", $code, $previous);
+    }
+
+    /**
+     * @return string the user-friendly name of this exception
+     */
+    public function getName()
+    {
+        return 'Unknown command';
+    }
+
+    public function suggestAlternatives()
+    {
+        $help = $this->application->createController('help');
+        if ($help === false) {
+            return [];
+        }
+        /** @var $helpController HelpController */
+        list($helpController, $actionID) = $help;
+
+        $availableActions = [];
+        $commands = $helpController->getCommands();
+        foreach ($commands as $command) {
+            $result = $this->application->createController($command);
+            if ($result === false) {
+                continue;
+            }
+            // add the command itself (default action)
+            $availableActions[] = $command;
+
+            // add all actions of this controller
+            /** @var $controller Controller */
+            list($controller, $actionID) = $result;
+            $actions = $helpController->getActions($controller);
+            if (!empty($actions)) {
+                $prefix = $controller->getUniqueId();
+                foreach ($actions as $action) {
+                    $availableActions[] = $prefix . '/' . $action;
+                }
+            }
+        }
+        $availableActions = $this->filterBySimilarity($availableActions);
+
+        asort($availableActions);
+        return $availableActions;
+    }
+
+    private function filterBySimilarity($actions)
+    {
+        // TODO
+        return $actions;
+    }
+}