Old description

  render( ,   = []): ;

PSR Template Renderer Proposal

A proposal for psr for rendering templates.

It is common that a library, application or CMSs need to have a template renderer / engine for rendering data for their websites or emails.

More and more application are going here to support data provider way. This application are the one which would benifit from the TemplateRendererInterface as they not only can provide them headless over an API but also make it possible that somebody can render the data via a Template Engine.

As a library author I want to make it free that my service can be used with any template engine the developer want to use. Typical usecases are PHP rendered CMSs like Sulu, Typo3, Drupal, Contao which maybe could benifit from this. But also all other data provider based libraries which ship configureable controller or have template to render like email tools / libraries.

Also for projects when somebody wants maybe switch in future from twig to latte templates as it consider better safety for xss a common interface can benifit here and avoid refractorings.

Defining the scope

The scope of the TemplateRenderer is only on rendering a given template with a given context. The template render interface will not take care of registering template paths or how to configure the template engine to find the templates. Similar how PSR-18 HttpClient does not care how the client is created or configured.

Analysis

In this section I did analyse the following existing template engines and added example how the render there templates.

• Twig (Symfony, Sulu CMS, Drupal, Contao (experimental))
• Smarty
• Latte (Nette)
• Laminas View
• Blade (Laravel)
• Fluid (Typo3)
• Contao (Contao CMS)
• Mezzio (Laminas) (already abstract Twig and Plates)
• Plates (PHP League)
• Mustache
• Yii View (Yii)

Repository: https://github.com/twigphp/Twig
Current Version: v3.4.1
Supported PHP Version: >=7.2.5
Template Type Hint: string|TemplateWrapper
Context Type Hint: array
Return Type Hint: string or output to buffer
Supports Stream: true

Render a template:

// render to variable
$content = $twig->render('test.template.twig', ['optional' => 'key-value']);

// render to output buffer
$twig->display('template.html.twig', ['optional' => 'value']);

Smarty

Repository: https://github.com/smarty-php/smarty
Current Version: v4.1.1
Supported PHP Version: ^7.1 || ^8.0
Template Type Hint: string
Context Type Hint: array
Return Type Hint: none
Supports Stream: true (only)

Render a template:

// render to output buffer
$smarty->assign('optional', 'value');
$smart->display('template.tpl');

Latte

Repository: https://github.com/nette/latte
Current Version: v3.0.0
Supported PHP Version: >=8.0 <8.2
Template Type Hint: string
Context Type Hint: object|mixed[]
Return Type Hint: string or output to buffer
Supports Stream: true

Render a template:

// render to variable
$latte->renderToString('template.latte', ['optional' => 'value']);

// render to output buffer
$latte->render('template.latte', ['optional' => 'value']);

Laminas View

Repository: https://github.com/laminas/laminas-view
Current Version: ^2.20.0
Supported PHP Version: ^7.4 || ~8.0.0 || ~8.1.0
Template Type Hint: string
Context Type Hint: ViewModel<null|array|Traversable|ArrayAccess>
Return Type Hint: null|string
Supports Stream: false

// render to variable
$viewModel = new ViewModel(['headline' => 'Example']);
$viewModel->setTemplate('index');
$content = $this->view($viewModel)->render();

Blade

Repository: https://github.com/illuminate/view
Current Version: v9.15.0
Supported PHP Version: ^8.1
Template Type Hint: string
Context Type Hint: array
Return Type Hint: string
Supports Stream: false ?

Render a template:

// render to variable
$content = view('welcome', ['name' => 'Samantha']);
// same as:
$content = $viewFactory->make($view, $data, $mergeData)->render();

Fluid

Repository: https://github.com/TYPO3/Fluid
Current Version: 2.7.1
Supported PHP Version: >=5.5.0
Template Type Hint: string
Context Type Hint: array
Return Type Hint: string
Supports Stream: false ?

// render to variable
$view = new StandaloneView();
$view->setTemplatePathAndFilename('template.html');
$view->assignMultiple(['optional' => 'key-value']);
$content = $view->render();

Contao

Repository: https://github.com/contao/core-bundle
Current Version: 4.13.4
Supported PHP Version: ^7.4 || ^8.0
Template Type Hint: string
Context Type Hint: object<string, mixed> via dynamic properties
Return Type Hint: string
Supports Stream: false ?

// render to variable
$template = new FrontendTemplate('template');
$template->optional = 'value';
$content = $template->parse();

Mezzio

Repository: https://github.com/mezzio/mezzio
Current Version: 3.10.0
Supported PHP Version: ~7.4.0||~8.0.0||~8.1.0
Template Type Hint: string
Context Type Hint: array|object
Return Type Hint: string
Supports Stream: false

// render to variable
$content = $templateRenderer->render('template', ['optional' => 'value']);

Plates

Repository: https://github.com/thephpleague/plates
Current Version: v3.4.0
Supported PHP Version: ^7.0|^8.0
Template Type Hint: string
Context Type Hint: array
Return Type Hint: string
Supports Stream: false

// render to variable
$content = $plates->render('template', ['optional' => 'value']);

Mustache

Repository: https://github.com/bobthecow/mustache.php
Current Version: v2.14.1
Supported PHP Version: >=5.2.4
Template Type Hint: string
Context Type Hint: array
Return Type Hint: string
Supports Stream: false

// render to variable
$content = $mustache->render('template', ['optional' => 'value']);

Yii View

Repository: https://github.com/yiisoft/view
Current Version: 5.0.0
Supported PHP Version: ^7.4|^8.0
Template Type Hint: string
Context Type Hint: array
Return Type Hint: string
Supports Stream: false

// render to variable
$content = $view->render('template', ['optional' => 'value']);

Spiral View

Repository: https://github.com/spiral/views
Current Version: 2.13.1
Supported PHP Version: >=^7.4
Template Type Hint: string
Context Type Hint: array
Return Type Hint: string
Supports Stream: ?

// render to variable
$content = $view->render('template', ['optional' => 'value']);

The proposal

The interface for a TemplateRender I would recommend is the following based on my analysis of exist template engines and what is the easiest way to put them together and have maximum interoperability:

/**
 * Render the template with the given context data.
 *
 * @param string $template
 * @param array<string, mixed> $context
 *
 * @return string
 *
 * @throw TemplateNotFoundExceptionInterface
 */
public function render(string $template, array $context = []): string;

For maximum compatibility we even could consider to publish 2 version of the template renderer v1 without typehints so exist template engine still supporting old php version can already implement it and v2 with typehints.

Exist TemplateRenderer Discussion

There was already an exist disussion about implementing a TemplateRendererInterface here: https://groups.google.com/g/php-fig/c/w1cugJ9DaFg/m/TPTnYY5LBgAJ.

The discussion goes over several topics just to mention the main parts:

• Template should be objects
• Context should be objects
• TemplateRender should stream to output even asynchronity

To target this specific points. I would focus in this PSR on exist solution as we see most work for template with logical string based names and do not require an object.

I want mention here also developer experience as example in the past why there was created PSR 16 (Simple Cache) where we did still have PSR 6.

So the name of the proposal should maybe be "Simple TemplateRenderer" and not try to reinventing the wheel.

By analysing exist template engine, not everybody support to have an object as a context so I would keep the interface to array for context only. This way it is easy to make exist template engine compatible with PSR interface.

For streaming the output I must say I did not see one project since 7 years which did use for example the streaming functionality of twig and for maximum compatibility I would also remove that requirement from the PSR as the analysis give there are template engines which do not support that functionality.

The proposal I did write can be found here: https://github.com/php-fig/fig-standards/pull/1280/files. I know I did skip here some process by already writing something, still I hope we can put most of the template engine creators / maintainers on one template to dicuss if they are willing to add such an interface or for which we maybe can provide a bridge, so system like CMSs, Librariy, Newsletter Tools, can make use of it. I will also bring this topic on the table for our next CMS Garden call which we have every month where several members of different CMS have a call together discussion common topics.

TODO List

• Create list which libraries would benifite using a TemplateRendererInterface and which would not
• Analyse exist Template engine of their ability to check if a template exist or not

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