Fix an infinite recursion caused by missing plugin

When a MissingPluginException has caught when rendering an exception,
we should disable the plugin as needed to prevent an infinite recursion.

lib/Cake/Error/ExceptionRenderer.php

@@ -285,6 +285,12 @@ class ExceptionRenderer {
 			} else {
 				$this->_outputMessage('error500');
 			}
+		} catch (MissingPluginException $e) {
+			$attributes = $e->getAttributes();
+			if (isset($attributes['plugin']) && $attributes['plugin'] === $this->controller->plugin) {
+				$this->controller->plugin = null;
+			}
+			$this->_outputMessageSafe('error500');
 		} catch (Exception $e) {
 			$this->_outputMessageSafe('error500');
 		}

lib/Cake/Test/Case/Error/ExceptionRendererTest.php

@@ -764,6 +764,73 @@ class ExceptionRendererTest extends CakeTestCase {
 		$this->assertEquals('Errors', $ExceptionRenderer->controller->viewPath);
 	}
 
+/**
+ * Test that missing plugin disables Controller::$plugin if the two are the same plugin.
+ *
+ * @return void
+ */
+	public function testMissingPluginRenderSafe() {
+		$exception = new NotFoundException();
+		$ExceptionRenderer = new ExceptionRenderer($exception);
+
+		$ExceptionRenderer->controller = $this->getMock('Controller', array('render'));
+		$ExceptionRenderer->controller->plugin = 'TestPlugin';
+		$ExceptionRenderer->controller->request = $this->getMock('CakeRequest');
+
+		$exception = new MissingPluginException(array('plugin' => 'TestPlugin'));
+		$ExceptionRenderer->controller->expects($this->once())
+			->method('render')
+			->with('error400')
+			->will($this->throwException($exception));
+
+		$response = $this->getMock('CakeResponse');
+		$response->expects($this->once())
+			->method('body')
+			->with($this->logicalAnd(
+				$this->logicalNot($this->stringContains('test plugin error500')),
+				$this->stringContains('Not Found')
+			));
+
+		$ExceptionRenderer->controller->response = $response;
+		$ExceptionRenderer->render();
+	}
+
+/**
+ * Test that missing plugin doesn't disable Controller::$plugin if the two aren't the same plugin.
+ *
+ * @return void
+ */
+	public function testMissingPluginRenderSafeWithPlugin() {
+		App::build(array(
+			'Plugin' => array(CAKE . 'Test' . DS . 'test_app' . DS . 'Plugin' . DS)
+		), App::RESET);
+		CakePlugin::load('TestPlugin');
+		$exception = new NotFoundException();
+		$ExceptionRenderer = new ExceptionRenderer($exception);
+
+		$ExceptionRenderer->controller = $this->getMock('Controller', array('render'));
+		$ExceptionRenderer->controller->plugin = 'TestPlugin';
+		$ExceptionRenderer->controller->request = $this->getMock('CakeRequest');
+
+		$exception = new MissingPluginException(array('plugin' => 'TestPluginTwo'));
+		$ExceptionRenderer->controller->expects($this->once())
+			->method('render')
+			->with('error400')
+			->will($this->throwException($exception));
+
+		$response = $this->getMock('CakeResponse');
+		$response->expects($this->once())
+			->method('body')
+			->with($this->logicalAnd(
+				$this->stringContains('test plugin error500'),
+				$this->stringContains('Not Found')
+			));
+
+		$ExceptionRenderer->controller->response = $response;
+		$ExceptionRenderer->render();
+		CakePlugin::unload();
+	}
+
 /**
  * Test that exceptions can be rendered when an request hasn't been registered
  * with Router

lib/Cake/Test/test_app/Plugin/TestPlugin/View/Errors/error500.ctp

@@ -0,0 +1,11 @@
+test plugin error500
+<h2><?php echo $message; ?></h2>
+<p class="error">
+	<strong><?php echo __d('cake', 'Error'); ?>: </strong>
+	<?php echo __d('cake', 'An Internal Error Has Occurred.'); ?>
+</p>
+<?php
+if (Configure::read('debug') > 0):
+	echo $this->element('exception_stack_trace');
+endif;
+?>