Make extending a missing element throw an exception

A layout extending a missing layout throws a missing-layout exception
A view extendinga missing view throws a missing-view exception
Now, an element extending a missing element throws a logic exception

in addition "absolute" paths can be used such that (using elements as an
example)

$this->extend('foo') - extends View/Elements/foo.ctp
$this->extend('/foo') - extends View/foo.ctp

Closes #2504

lib/Cake/Test/Case/View/ViewTest.php

@@ -1392,7 +1392,6 @@ public function testExtendLoop() {
 		$this->View->render('extend_loop');
 	}
 
-
 /**
  * Test extend() in an element and a view.
  *
@@ -1411,6 +1410,17 @@ public function testExtendElement() {
 		$this->assertEquals($expected, $content);
 	}
 
+/**
+ * Extending an element which doesn't exist should throw a missing view exception
+ *
+ * @expectedException LogicException
+ * @return void
+ */
+	public function testExtendMissingElement() {
+		$this->View->layout = false;
+		$this->View->render('extend_missing_element');
+	}
+
 /**
  * Test that setting arbitrary properties still works.
  *

lib/Cake/Test/test_app/View/Elements/extended_missing_element.ctp

@@ -0,0 +1,2 @@
+<?php $this->extend('noneexistent_parent_element'); ?>
+Element content.

lib/Cake/Test/test_app/View/Posts/extend_missing_element.ctp

@@ -0,0 +1 @@
+<?php echo $this->element('extended_missing_element'); ?>

lib/Cake/View/View.php

@@ -662,24 +662,34 @@ public function end() {
  * @param string $name The view or element to 'extend' the current one with.
  * @return void
  * @throws LogicException when you extend a view with itself or make extend loops.
+ * @throws LogicException when you extend an element which doesn't exist
  */
 	public function extend($name) {
-		switch ($this->_currentType) {
-			case self::TYPE_VIEW:
-				$parent = $this->_getViewFileName($name);
-			break;
-			case self::TYPE_ELEMENT:
-				$parent = $this->_getElementFileName($name);
-			break;
-			case self::TYPE_LAYOUT:
-				$parent = $this->_getLayoutFileName($name);
-			break;
-
+		if ($name[0] === '/' || $this->_currentType === self::TYPE_VIEW) {
+			$parent = $this->_getViewFileName($name);
+		} else {
+			switch ($this->_currentType) {
+				case self::TYPE_ELEMENT:
+					$parent = $this->_getElementFileName($name);
+					if (!$parent) {
+						list($plugin, $name) = $this->_pluginSplit($name);
+						$paths = $this->_paths($plugin);
+						$defaultPath = $paths[0] . 'Elements' . DS;
+						throw new LogicException(__d(
+							'cake_dev',
+							'You cannot extend an element which does not exist (%s).',
+							$defaultPath . $name . $this->ext
+						));
+					}
+					break;
+				case self::TYPE_LAYOUT:
+					$parent = $this->_getLayoutFileName($name);
+					break;
+				default:
+					$parent = $this->_getViewFileName($name);
+			}
 		}
 
-		if (!$parent) {
-			throw new LogicException(__d('cake_dev', 'The parent %s you specified doesn\'t exist.', $this->_currentType));
-		}
 		if ($parent == $this->_current) {
 			throw new LogicException(__d('cake_dev', 'You cannot have views extend themselves.'));
 		}