visitors.md

Stempler - AST Modifications

Stempler template engine fully exposes template AST (DOM) and provides API for the modifications similar to https://github.com/nikic/PHP-Parser.

You can create magical (in both ways) workflows and helpers by implementing your Node Visitors.

You can read more about how traversing works here.

Create Visitor

To create AST visitor you must implement interface provided by Stempler engine - Spiral\Stempler\VisitorInterface.

We will try to create visitor which automatically adds alt attribute to all img tags found in your templates:

use Spiral\Stempler\Node\HTML;
use Spiral\Stempler\VisitorContext;
use Spiral\Stempler\VisitorInterface;

class AltImageVisitor implements VisitorInterface
{
    public function enterNode($node, VisitorContext $ctx)
    {
    }

    public function leaveNode($node, VisitorContext $ctx)
    {
        if ($node instanceof HTML\Tag && $node->name === 'img') {
            $alt = null;
            foreach ($node->attrs as $attr) {
                if ($attr->name === 'alt') {
                    $alt = $attr;
                    break;
                }
            }

            if ($alt === null) {
                $node->attrs[] = new HTML\Attr('alt', '"this is image alt"');
            }
        }
    }
}

You can inject other tags or even PHP into your templates.

Register Visitor

Call StemplerBootloader->addVistitor to register visitor in the template engine. We can do it using application bootloader:

namespace App\Bootloader;

use App\Visitor\AltImageVisitor;
use Spiral\Boot\Bootloader\Bootloader;
use Spiral\Stempler\Bootloader\StemplerBootloader;

class AltImageBootloader extends Bootloader
{
    public function boot(StemplerBootloader $stempler)
    {
        $stempler->addVisitor(AltImageVisitor::class);
    }
}

You have clean view cache to view newly applied changes.

Now all the img tags will always include alt attribute.