New View Layout functionality for simple template functionality.

system/View/View.php

@@ -119,6 +119,29 @@ class View implements RendererInterface
 	 */
 	protected $viewsCount = 0;
 
+	/**
+	 * The name of the layout being used, if any.
+	 * Set by the `extend` method used within views.
+	 *
+	 * @var string
+	 */
+	protected $layout;
+
+	/**
+	 * Holds the sections and their data.
+	 *
+	 * @var array
+	 */
+	protected $sections = [];
+
+	/**
+	 * The name of the current section being rendered,
+	 * if any.
+	 *
+	 * @var string
+	 */
+	protected $currentSection;
+
 	//--------------------------------------------------------------------
 
 	/**
@@ -211,6 +234,16 @@ public function render(string $view, array $options = null, $saveData = null): s
 		$output = ob_get_contents();
 		@ob_end_clean();
 
+		// When using layouts, the data has already been stored
+		// in $this->sections, and no other valid output
+		// is allowed in $output so we'll overwrite it.
+		if (! is_null($this->layout))
+		{
+			$layoutView   = $this->layout;
+			$this->layout = null;
+			$output       = $this->render($layoutView, $options, $saveData);
+		}
+
 		$this->logPerformance($this->renderVars['start'], microtime(true), $this->renderVars['view']);
 
 		if (CI_DEBUG && (! isset($options['debug']) || $options['debug'] === true))
@@ -376,6 +409,82 @@ public function getData()
 
 	//--------------------------------------------------------------------
 
+	/**
+	 * Specifies that the current view should extend an existing layout.
+	 *
+	 * @param string $layout
+	 *
+	 * @return $this
+	 */
+	public function extend(string $layout)
+	{
+		$this->layout = $layout;
+	}
+
+	//--------------------------------------------------------------------
+
+	/**
+	 * Starts holds content for a section within the layout.
+	 *
+	 * @param string $name
+	 */
+	public function section(string $name)
+	{
+		$this->currentSection = $name;
+
+		ob_start();
+	}
+
+	//--------------------------------------------------------------------
+
+	/**
+	 *
+	 *
+	 * @throws \Zend\Escaper\Exception\RuntimeException
+	 */
+	public function endSection()
+	{
+		$contents = ob_get_clean();
+
+		if (empty($this->currentSection))
+		{
+			throw new \RuntimeException('View themes, no current section.');
+		}
+
+		// Ensure an array exists so we can store multiple entries for this.
+		if (! array_key_exists($this->currentSection, $this->sections))
+		{
+			$this->sections[$this->currentSection] = [];
+		}
+		$this->sections[$this->currentSection][] = $contents;
+
+		$this->currentSection = null;
+	}
+
+	//--------------------------------------------------------------------
+
+	/**
+	 * Renders a section's contents.
+	 *
+	 * @param string $sectionName
+	 */
+	public function renderSection(string $sectionName)
+	{
+		if (! isset($this->sections[$sectionName]))
+		{
+			echo '';
+
+			return;
+		}
+
+		foreach ($this->sections[$sectionName] as $contents)
+		{
+			echo $contents;
+		}
+	}
+
+	//--------------------------------------------------------------------
+
 	/**
 	 * Returns the performance data that might have been collected
 	 * during the execution. Used primarily in the Debug Toolbar.

tests/system/View/ViewTest.php

@@ -266,4 +266,33 @@ public function testPerformanceNonLogging()
 		$this->assertEquals(0, count($view->getPerformanceData()));
 	}
 
+	public function testRenderLayoutExtendsCorrectly()
+	{
+		$view = new View($this->config, $this->viewsDir, $this->loader);
+
+		$view->setVar('testString', 'Hello World');
+		$expected = "<p>Open</p>\n<h1>Hello World</h1>";
+
+		$this->assertContains($expected, $view->render('extend'));
+	}
+
+	public function testRenderLayoutMakesDataAvailableToBoth()
+	{
+		$view = new View($this->config, $this->viewsDir, $this->loader);
+
+		$view->setVar('testString', 'Hello World');
+		$expected = "<p>Open</p>\n<h1>Hello World</h1>\n<p>Hello World</p>";
+
+		$this->assertContains($expected, $view->render('extend'));
+	}
+
+	public function testRenderLayoutSupportsMultipleOfSameSection()
+	{
+		$view = new View($this->config, $this->viewsDir, $this->loader);
+
+		$view->setVar('testString', 'Hello World');
+		$expected = "<p>First</p>\n<p>Second</p>";
+
+		$this->assertContains($expected, $view->render('extend_two'));
+	}
 }

tests/system/View/Views/extend.php

@@ -0,0 +1,5 @@
+<?= $this->extend('layout') ?>
+
+<?= $this->section('content') ?>
+<h1><?= $testString ?></h1>
+<?= $this->endSection() ?>

tests/system/View/Views/extend_two.php

@@ -0,0 +1,10 @@
+<?= $this->extend('layout') ?>
+
+<?= $this->section('content') ?>
+<p>First</p>
+<?= $this->endSection() ?>
+
+
+<?= $this->section('content') ?>
+<p>Second</p>
+<?= $this->endSection() ?>

tests/system/View/Views/layout.php

@@ -0,0 +1,3 @@
+<p>Open</p>
+<?= $this->renderSection('content') ?>
+<p><?= $testString ?></p>

user_guide_src/source/changelogs/next.rst

@@ -4,6 +4,7 @@ Version |version|
 Release Date: Not released
 
 Highlights:
+- New View Layouts provide simple way to create site site view templates.
 
 
 The list of changed files follows, with PR numbers shown.

user_guide_src/source/outgoing/index.rst

@@ -10,6 +10,7 @@ View components are used to build what is returned to the user.
     views
     view_cells
     view_renderer
+    view_layouts
     view_parser
     response
     api_responses

user_guide_src/source/outgoing/view_layouts.rst

@@ -0,0 +1,74 @@
+############
+View Layouts
+############
+
+.. contents::
+    :local:
+    :depth: 2
+
+CodeIgniter supports a simple, yet very flexible, layout system that makes it simple to use one or more
+base page layouts across your application. Layouts support sections of content that can be inserted from
+any view being rendered. You could create different layouts to support one-column, two-column,
+blog archive pages, and more. Layouts are never directly rendered. Instead, you render a view, which
+specifies the layout that it wants to extend.
+
+*****************
+Creating A Layout
+*****************
+
+Layouts are views like any other. The only difference is their intended usage. Layouts are the only view
+files that would make use of the ``renderSection()`` method. This method acts as a placeholder for content.
+
+::
+
+    <!doctype html>
+    <html>
+    <head>
+        <title>My Layout</title>
+    </head>
+    <body>
+        <?= $this->renderSection('content') ?>
+    </body>
+    </html>
+
+The renderSection() method only has one argument - the name of the section. That way any child views know
+what to name the content section.
+
+**********************
+Using Layouts in Views
+**********************
+
+Whenveer a view wants to be inserted into a layout, it must use the ``extend()`` method at the top of the file::
+
+    <?= $this->extend('default') ?>
+
+The extend method takes the name of any view file that you wish to use. Since they are standard views, they will
+be located just like a view. By default, it will look in the application's View directory, but will also scan
+other PSR-4 defined namespaces. You can include a namespace to locate the view in particular namespace View directory::
+
+    <?= $this->extend('Blog\Views\default') ?>
+
+All content within a view that extends a layout must be included within ``section($name)`` and ``endSection()`` method calls.
+Any content between these calls will be inserted into the layout wherever the ``renderSection($name)`` call that
+matches the section name exists.::
+
+    <?= $this->extend('default') ?>
+
+    <?= $this->section('content') ?>
+        <h1>Hello World!</h1>
+    <?= $this->endSection() ?>
+
+The ``endSection()`` does not need the section name. It automatically knows which one to close.
+
+******************
+Rendering the View
+******************
+
+Rendering the view and it's layout is done exactly as any other view would be displayed within a controller::
+
+    public function index()
+    {
+        echo view('some_view');
+    }
+
+The renderer is smart enough to detect whether the view should be rendered on its own, or if it needs a layout.