Advanced template engine functionnality (blocks)

Post by **Nicofuma** » Thu May 29, 2014 11:43 pm

Twig is a very powerful template engine which come with some advanced features. One of them is the ability to structure the template in blocks and to use a template inheritance trough them (http://twig.sensiolabs.org/doc/template ... nheritance - http://twig.sensiolabs.org/doc/tags/extends.html).
Example:
The base template: base.html

Code: Select all

<!DOCTYPE html>
<html>
    <head>
        {% block head %}
            <link rel="stylesheet" href="style.css" />
            <title>{% block title %}{% endblock %} - My Webpage</title>
        {% endblock %}
    </head>
    <body>
        <div id="content">{% block content %}Base content{% endblock %}</div>
        <div id="footer">
            {% block footer %}
                &copy; Copyright 2011 by <a href="http://domain.invalid/">you</a>.
            {% endblock %}
        </div>
    </body>
</html>

And a child template: child.html

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{% extends "base.html" %}

{% block title %}Index{% endblock %}
{% block head %}
    {{ parent() }}
    <style type="text/css">
        .important { color: #336699; }
    </style>
{% endblock %}
{% block content %}
    <h1>Index</h1>
    <p class="important">
        Welcome to my awesome homepage.
    </p>
{% endblock %}

Then, in the php code we ask to render the child template and this code is generated:

Code: Select all

!DOCTYPE html>
<html>
    <head>
            <link rel="stylesheet" href="style.css" />
            <title>Index - My Webpage</title>
    <style type="text/css">
        .important { color: #336699; }
    </style>
    </head>
    <body>
        <div id="content">    <h1>Index</h1>
    <p class="important">
        Welcome to my awesome homepage.
    </p></div>
        <div id="footer">=
                &copy; Copyright 2011 by <a href="http://domain.invalid/">you</a>.=
        </div>
    </body>
</html>

That's template inheritance and it's already available in phpBB.

But it's not the only way to use the blocks because at any time we can request Twig to render a specific block in a given template but to send this request we need to have the Template element himself and that is currently not possible. It can be useful to define many different blocks for a set of module (ie: menu, toolbar, content, footer...) and then render each block of each module in different places in the code.
Example:

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[...]
{% for template in templates %}
{{ template.renderBlock('menu', {<arguments>}) }}
{% endfor %}
[...]
{% for template in templates %}
{{ template.renderBlock('footer', {<arguments>}) }}
{% endfor %}
[...]

This behavior can be simulate by two different ways:

Define one template file per block and include them

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[...]
{% for module_name in modules %}
{% include module_name ~ '_menu.html' %}
{% endfor %}
[...]
{% for module_name in modules %}
{% include module_name ~ '_footer.html' %}
{% endfor %}
[...]

Define a variable in the base template and use a combination of if in the included template
Base template

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[...]
{% for template_path in templates %}
{% include template_path with { 'in_menu': true } %}
{% endfor %}
[...]
{% for template_path in templates %}
{% include template_path with { 'in_footer': true } %}
{% endfor %}
[...]

Included template

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{% if in_menu %}
MENU
{% endif %}
{% if in_footer %}
FOOTER
{% endif %}

So now the question is: Do we want to support this feature? And if the answer is yes how should we do?

Now we are using Twig and \phpbb\template\template is only a BC interface => the template engine can extends \Twig_Environment and implements the interface
\phpbb\template\template is a generic interface which allows us to change the template engine without changing all the code, only the templates could have to be updated => we can provide a get_engine() method to get the real template engine but in this case we can return anything and the user has to manage with (he has to test which engine is returned and then generate an appropriate code)

-------------------------
personally, after some thought,i don't think that we should support this feature but in the other case we should use the first solution (extend \Twig_Environment)

Post by **MattF** » Wed Jun 18, 2014 11:22 pm

This would be good for allowing extensions to replace blocks with new blocks. Right now extensions can only add to the template, not replace/overwrite.

rfdy · Post by **rfdy** » Fri Jun 20, 2014 2:05 pm

There are a few threads (and jiras) about doing this, ie. making full use of Twig's power.

+1

Post by **Nicofuma** » Fri Jun 20, 2014 2:53 pm

But the real question is somewhere else: do we want to keep a generic (and so limited) interface to be able to replace the template engine later or do we want to abandon this interface?

nickvergessen · Post by **nickvergessen** » Fri Jun 20, 2014 3:14 pm

We can also add <-- BLOCK --> to the phpBB interface and then mirror it just like all the other constructions?

Post by **Nicofuma** » Fri Jun 20, 2014 3:25 pm

for the blocks it should be feasible

rfdy · Post by **rfdy** » Fri Jun 20, 2014 3:53 pm

Not sure why you'd want to preserve phpbb's ancient template syntax. Modern IDEs support twig, and many projects are moving to twig (drupal, et al), so the more standard syntax it is kept the better.

Post by **Nicofuma** » Fri Jun 20, 2014 5:07 pm

the question is not the syntax, but the php interface. (and the old syntax is very good for some designers, because the syntax of twig can be very complicated for some of them)

Post by **MattF** » Fri Jun 20, 2014 5:13 pm

rfdy wrote:Not sure why you'd want to preserve phpbb's ancient template syntax. Modern IDEs support twig, and many projects are moving to twig (drupal, et al), so the more standard syntax it is kept the better.

because hundreds of styles are built on it and authors are used to it, and preserving it will allow authors to more easily update their styles to 3.1. Jumping straight into Twig only Syntax with no preservation of traditional syntax could create a black hole in new style development. And that could then result in decreased adoption of phpBB 3.1 by users who see no useable styles for ready for it.

The idea is to switch to Twig only gradually, by version 3.2.

Post by **Nicofuma** » Fri Jun 20, 2014 5:18 pm

the syntax of the template files is definitely not a problem: we can use the two syntaxes in the same template file. Currently the only limitation is made by the php interface (\phpbb\template\template) because the Twig object is encapsulated and to keep a generic interface we can't access it directly.

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Advanced template engine functionnality (blocks)

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