Allow string values for templates option.

This allows template files to be used with input(). This makes input()
consistent with create() and allows developers to use config files
better/more easily.

Refs #4015

src/View/Helper/FormHelper.php

@@ -893,7 +893,8 @@ class FormHelper extends Helper {
 
 		if ($newTemplates) {
 			$templater->push();
-			$templater->add($options['templates']);
+			$templateMethod = is_string($options['templates']) ? 'load' : 'add';
+			$templater->{$templateMethod}($options['templates']);
 		}
 		unset($options['templates']);
 

tests/TestCase/View/Helper/FormHelperTest.php

@@ -2108,6 +2108,28 @@ class FormHelperTest extends TestCase {
 	}
 
 /**
+ * Test that input() accepts a template file.
+ *
+ * @return void
+ */
+	public function testInputWithTemplateFile() {
+		$result = $this->Form->input('field', array(
+			'templates' => 'htmlhelper_tags'
+		));
+		$expected = array(
+			'label' => array('for' => 'field'),
+			'Field',
+			'/label',
+			'input' => array(
+				'type' => 'text', 'name' => 'field',
+				'id' => 'field'
+			),
+		);
+		$this->assertTags($result, $expected);
+
+	}
+
+/**
  * Test id prefix
  *
  * @return void

tests/test_app/TestApp/Config/htmlhelper_tags.php

@@ -3,5 +3,6 @@
 $config = [
 	'formstart' => 'start form',
 	'formend' => 'finish form',
-	'hiddenblock' => '<div class="hidden">{{content}}</div>'
+	'hiddenblock' => '<div class="hidden">{{content}}</div>',
+	'inputContainer' => '{{content}}'
 ];