Extending Twig¶
Twig can be extended in many ways; you can add extra tags, filters, tests, operators, global variables, and functions. You can even extend the parser itself with node visitors.
Note
The first section of this chapter describes how to extend Twig. If you want to reuse your changes in different projects or if you want to share them with others, you should then create an extension as described in the following section.
Caution
When extending Twig without creating an extension, Twig won’t be able to recompile your templates when the PHP code is updated. To see your changes in real-time, either disable template caching or package your code into an extension (see the next section of this chapter).
Before extending Twig, you must understand the differences between all the different possible extension points and when to use them.
First, remember that Twig has two main language constructs:
{{ }}
: used to print the result of an expression evaluation;{% %}
: used to execute statements.
To understand why Twig exposes so many extension points, let’s see how to implement a Lorem ipsum generator (it needs to know the number of words to generate).
You can use a lipsum
tag:
{% lipsum 40 %}
That works, but using a tag for lipsum
is not a good idea for at least
three main reasons:
lipsum
is not a language construct;The tag outputs something;
The tag is not flexible as you cannot use it in an expression:
{{ 'some text' ~ {% lipsum 40 %} ~ 'some more text' }}
In fact, you rarely need to create tags; and that’s good news because tags are the most complex extension point.
Now, let’s use a lipsum
filter:
{{ 40|lipsum }}
Again, it works. But a filter should transform the passed value to something
else. Here, we use the value to indicate the number of words to generate (so,
40
is an argument of the filter, not the value we want to transform).
Next, let’s use a lipsum
function:
{{ lipsum(40) }}
Here we go. For this specific example, the creation of a function is the extension point to use. And you can use it anywhere an expression is accepted:
{{ 'some text' ~ lipsum(40) ~ 'some more text' }}
{% set lipsum = lipsum(40) %}
Lastly, you can also use a global object with a method able to generate lorem ipsum text:
{{ text.lipsum(40) }}
As a rule of thumb, use functions for frequently used features and global objects for everything else.
Keep in mind the following when you want to extend Twig:
What? |
Implementation difficulty? |
How often? |
When? |
---|---|---|---|
macro |
simple |
frequent |
Content generation |
global |
simple |
frequent |
Helper object |
function |
simple |
frequent |
Content generation |
filter |
simple |
frequent |
Value transformation |
tag |
complex |
rare |
DSL language construct |
test |
simple |
rare |
Boolean decision |
operator |
simple |
rare |
Values transformation |
Globals¶
Global variables are available in all templates and macros. Use addGlobal()
to add a global variable to a Twig environment:
$twig = new \Twig\Environment($loader);
$twig->addGlobal('text', new Text());
You can then use the text
variable anywhere in a template:
{{ text.lipsum(40) }}
Filters¶
Creating a filter consists of associating a name with a PHP callable:
// an anonymous function
$filter = new \Twig\TwigFilter('rot13', function ($string) {
return str_rot13($string);
});
// or a simple PHP function
$filter = new \Twig\TwigFilter('rot13', 'str_rot13');
// or a class static method
$filter = new \Twig\TwigFilter('rot13', ['SomeClass', 'rot13Filter']);
$filter = new \Twig\TwigFilter('rot13', 'SomeClass::rot13Filter');
// or a class method
$filter = new \Twig\TwigFilter('rot13', [$this, 'rot13Filter']);
// the one below needs a runtime implementation (see below for more information)
$filter = new \Twig\TwigFilter('rot13', ['SomeClass', 'rot13Filter']);
The first argument passed to the \Twig\TwigFilter
constructor is the name of the
filter you will use in templates and the second one is the PHP callable to
associate with it.
Then, add the filter to the Twig environment:
$twig = new \Twig\Environment($loader);
$twig->addFilter($filter);
And here is how to use it in a template:
{{ 'Twig'|rot13 }}
{# will output Gjvt #}
When called by Twig, the PHP callable receives the left side of the filter
(before the pipe |
) as the first argument and the extra arguments passed
to the filter (within parentheses ()
) as extra arguments.
For instance, the following code:
{{ 'TWIG'|lower }}
{{ now|date('d/m/Y') }}
is compiled to something like the following:
<?php echo strtolower('TWIG') ?>
<?php echo twig_date_format_filter($now, 'd/m/Y') ?>
The \Twig\TwigFilter
class takes an array of options as its last argument:
$filter = new \Twig\TwigFilter('rot13', 'str_rot13', $options);
Charset-aware Filters¶
If you want to access the default charset in your filter, set the
needs_charset
option to true
; Twig will pass the default charset as the
first argument to the filter call:
$filter = new \Twig\TwigFilter('rot13', function (string $charset, $string) {
return str_rot13($string);
}, ['needs_charset' => true]);
Environment-aware Filters¶
If you want to access the current environment instance in your filter, set the
needs_environment
option to true
; Twig will pass the current
environment as the first argument to the filter call:
$filter = new \Twig\TwigFilter('rot13', function (\Twig\Environment $env, $string) {
// get the current charset for instance
$charset = $env->getCharset();
return str_rot13($string);
}, ['needs_environment' => true]);
Context-aware Filters¶
If you want to access the current context in your filter, set the
needs_context
option to true
; Twig will pass the current context as
the first argument to the filter call (or the second one if
needs_environment
is also set to true
):
$filter = new \Twig\TwigFilter('rot13', function ($context, $string) {
// ...
}, ['needs_context' => true]);
$filter = new \Twig\TwigFilter('rot13', function (\Twig\Environment $env, $context, $string) {
// ...
}, ['needs_context' => true, 'needs_environment' => true]);
Automatic Escaping¶
If automatic escaping is enabled, the output of the filter may be escaped
before printing. If your filter acts as an escaper (or explicitly outputs HTML
or JavaScript code), you will want the raw output to be printed. In such a
case, set the is_safe
option:
$filter = new \Twig\TwigFilter('nl2br', 'nl2br', ['is_safe' => ['html']]);
Some filters may need to work on input that is already escaped or safe, for
example when adding (safe) HTML tags to originally unsafe output. In such a
case, set the pre_escape
option to escape the input data before it is run
through your filter:
$filter = new \Twig\TwigFilter('somefilter', 'somefilter', ['pre_escape' => 'html', 'is_safe' => ['html']]);
Variadic Filters¶
When a filter should accept an arbitrary number of arguments, set the
is_variadic
option to true
; Twig will pass the extra arguments as the
last argument to the filter call as an array:
$filter = new \Twig\TwigFilter('thumbnail', function ($file, array $options = []) {
// ...
}, ['is_variadic' => true]);
Be warned that named arguments passed to a variadic filter cannot be checked for validity as they will automatically end up in the option array.
Dynamic Filters¶
A filter name containing the special *
character is a dynamic filter and
the *
part will match any string:
$filter = new \Twig\TwigFilter('*_path', function ($name, $arguments) {
// ...
});
The following filters are matched by the above defined dynamic filter:
product_path
category_path
A dynamic filter can define more than one dynamic parts:
$filter = new \Twig\TwigFilter('*_path_*', function ($name, $suffix, $arguments) {
// ...
});
The filter receives all dynamic part values before the normal filter arguments,
but after the environment and the context. For instance, a call to
'Paris'|a_path_b()
will result in the following arguments to be passed to the
filter: ('a', 'b', 'Paris')
.
Deprecated Filters¶
Added in version 3.15: The deprecation_info
option was added in Twig 3.15.
You can mark a filter as being deprecated by setting the deprecation_info
option:
$filter = new \Twig\TwigFilter('obsolete', function () {
// ...
}, ['deprecation_info' => new DeprecatedCallableInfo('twig/twig', '3.11', 'new_one')]);
The DeprecatedCallableInfo
constructor takes the following parameters:
The Composer package name that defines the filter;
The version when the filter was deprecated.
Optionally, you can also provide the following parameters about an alternative:
The package name that contains the alternative filter;
The alternative filter name that replaces the deprecated one;
The package version that added the alternative filter.
When a filter is deprecated, Twig emits a deprecation notice when compiling a template using it. See Displaying Deprecation Notices for more information.
Note
Before Twig 3.15, you can mark a filter as being deprecated by setting the
deprecated
option to true
. You can also give an alternative filter
that replaces the deprecated one when that makes sense:
$filter = new \Twig\TwigFilter('obsolete', function () {
// ...
}, ['deprecated' => true, 'alternative' => 'new_one']);
Added in version 3.11: The deprecating_package
option was added in Twig 3.11.
You can also set the deprecating_package
option to specify the package
that is deprecating the filter, and deprecated
can be set to the
package version when the filter was deprecated:
$filter = new \Twig\TwigFilter('obsolete', function () {
// ...
}, ['deprecated' => '1.1', 'deprecating_package' => 'twig/some-package']);
Functions¶
Functions are defined in the exact same way as filters, but you need to create
an instance of \Twig\TwigFunction
:
$twig = new \Twig\Environment($loader);
$function = new \Twig\TwigFunction('function_name', function () {
// ...
});
$twig->addFunction($function);
Functions support the same features as filters, except for the pre_escape
and preserves_safety
options.
Tests¶
Tests are defined in the exact same way as filters and functions, but you need
to create an instance of \Twig\TwigTest
:
$twig = new \Twig\Environment($loader);
$test = new \Twig\TwigTest('test_name', function () {
// ...
});
$twig->addTest($test);
Tests allow you to create custom application specific logic for evaluating boolean conditions. As a simple example, let’s create a Twig test that checks if objects are ‘red’:
$twig = new \Twig\Environment($loader);
$test = new \Twig\TwigTest('red', function ($value) {
if (isset($value->color) && $value->color == 'red') {
return true;
}
if (isset($value->paint) && $value->paint == 'red') {
return true;
}
return false;
});
$twig->addTest($test);
Test functions must always return true
/false
.
When creating tests you can use the node_class
option to provide custom test
compilation. This is useful if your test can be compiled into PHP primitives.
This is used by many of the tests built into Twig:
namespace App;
use Twig\Environment;
use Twig\Node\Expression\TestExpression;
use Twig\TwigTest;
$twig = new Environment($loader);
$test = new TwigTest(
'odd',
null,
['node_class' => OddTestExpression::class]);
$twig->addTest($test);
class OddTestExpression extends TestExpression
{
public function compile(\Twig\Compiler $compiler)
{
$compiler
->raw('(')
->subcompile($this->getNode('node'))
->raw(' % 2 != 0')
->raw(')')
;
}
}
The above example shows how you can create tests that use a node class. The node
class has access to one sub-node called node
. This sub-node contains the
value that is being tested. When the odd
filter is used in code such as:
{% if my_value is odd %}
The node
sub-node will contain an expression of my_value
. Node-based
tests also have access to the arguments
node. This node will contain the
various other arguments that have been provided to your test.
If you want to pass a variable number of positional or named arguments to the
test, set the is_variadic
option to true
. Tests support dynamic
names (see dynamic filters for the syntax).
Creating an Extension¶
The main motivation for writing an extension is to move often used code into a reusable class like adding support for internationalization. An extension can define tags, filters, tests, operators, functions, and node visitors.
Most of the time, it is useful to create a single extension for your project, to host all the specific tags and filters you want to add to Twig.
Tip
When packaging your code into an extension, Twig is smart enough to
recompile your templates whenever you make a change to it (when
auto_reload
is enabled).
An extension is a class that implements the following interface:
interface \Twig\Extension\ExtensionInterface
{
/**
* Returns the token parser instances to add to the existing list.
*
* @return \Twig\TokenParser\TokenParserInterface[]
*/
public function getTokenParsers();
/**
* Returns the node visitor instances to add to the existing list.
*
* @return \Twig\NodeVisitor\NodeVisitorInterface[]
*/
public function getNodeVisitors();
/**
* Returns a list of filters to add to the existing list.
*
* @return \Twig\TwigFilter[]
*/
public function getFilters();
/**
* Returns a list of tests to add to the existing list.
*
* @return \Twig\TwigTest[]
*/
public function getTests();
/**
* Returns a list of functions to add to the existing list.
*
* @return \Twig\TwigFunction[]
*/
public function getFunctions();
/**
* Returns a list of operators to add to the existing list.
*
* @return array<array> First array of unary operators, second array of binary operators
*/
public function getOperators();
}
To keep your extension class clean and lean, inherit from the built-in
\Twig\Extension\AbstractExtension
class instead of implementing the interface as it provides
empty implementations for all methods:
class CustomTwigExtension extends \Twig\Extension\AbstractExtension
{
}
This extension does nothing for now. We will customize it in the next sections.
You can save your extension anywhere on the filesystem, as all extensions must be registered explicitly to be available in your templates.
You can register an extension by using the addExtension()
method on your
main Environment
object:
$twig = new \Twig\Environment($loader);
$twig->addExtension(new CustomTwigExtension());
Tip
The Twig core extensions are great examples of how extensions work.
Globals¶
Global variables can be registered in an extension via the getGlobals()
method:
class CustomTwigExtension extends \Twig\Extension\AbstractExtension implements \Twig\Extension\GlobalsInterface
{
public function getGlobals(): array
{
return [
'text' => new Text(),
];
}
// ...
}
Caution
Globals are fetched once from extensions and then cached for the lifetime
of the Twig environment. It means that globals should not be used to store
values that can change during the lifetime of the Twig environment. For
instance, if you’re using an application server like RoadRunner or
FrankenPHP, you should not store values related to the current context (like
the HTTP request). If you do so, don’t forget to reset the cache between
requests by calling Environment::resetGlobals()
.
Functions¶
Functions can be registered in an extension via the getFunctions()
method:
class CustomTwigExtension extends \Twig\Extension\AbstractExtension
{
public function getFunctions()
{
return [
new \Twig\TwigFunction('lipsum', 'generate_lipsum'),
];
}
// ...
}
Filters¶
To add a filter to an extension, you need to override the getFilters()
method. This method must return an array of filters to add to the Twig
environment:
class CustomTwigExtension extends \Twig\Extension\AbstractExtension
{
public function getFilters()
{
return [
new \Twig\TwigFilter('rot13', 'str_rot13'),
];
}
// ...
}
Tags¶
Adding a tag in an extension can be done by overriding the
getTokenParsers()
method. This method must return an array of tags to add
to the Twig environment:
class CustomTwigExtension extends \Twig\Extension\AbstractExtension
{
public function getTokenParsers()
{
return [new CustomSetTokenParser()];
}
// ...
}
In the above code, we have added a single new tag, defined by the
CustomSetTokenParser
class. The CustomSetTokenParser
class is
responsible for parsing the tag and compiling it to PHP.
Operators¶
The getOperators()
methods lets you add new operators. Here is how to add
the !
, ||
, and &&
operators:
class CustomTwigExtension extends \Twig\Extension\AbstractExtension
{
public function getOperators()
{
return [
[
'!' => ['precedence' => 50, 'class' => \Twig\Node\Expression\Unary\NotUnary::class],
],
[
'||' => ['precedence' => 10, 'class' => \Twig\Node\Expression\Binary\OrBinary::class, 'associativity' => \Twig\ExpressionParser::OPERATOR_LEFT],
'&&' => ['precedence' => 15, 'class' => \Twig\Node\Expression\Binary\AndBinary::class, 'associativity' => \Twig\ExpressionParser::OPERATOR_LEFT],
],
];
}
// ...
}
Tests¶
The getTests()
method lets you add new test functions:
class CustomTwigExtension extends \Twig\Extension\AbstractExtension
{
public function getTests()
{
return [
new \Twig\TwigTest('even', 'twig_test_even'),
];
}
// ...
}
Definition vs Runtime¶
Twig filters, functions, and tests runtime implementations can be defined as any valid PHP callable:
functions/static methods: Simple to implement and fast (used by all Twig core extensions); but it is hard for the runtime to depend on external objects;
closures: Simple to implement;
object methods: More flexible and required if your runtime code depends on external objects.
The simplest way to use methods is to define them on the extension itself:
class CustomTwigExtension extends \Twig\Extension\AbstractExtension
{
private $rot13Provider;
public function __construct($rot13Provider)
{
$this->rot13Provider = $rot13Provider;
}
public function getFunctions()
{
return [
new \Twig\TwigFunction('rot13', [$this, 'rot13']),
];
}
public function rot13($value)
{
return $this->rot13Provider->rot13($value);
}
}
This is very convenient but not recommended as it makes template compilation depend on runtime dependencies even if they are not needed (think for instance as a dependency that connects to a database engine).
You can decouple the extension definitions from their runtime implementations by
registering a \Twig\RuntimeLoader\RuntimeLoaderInterface
instance on the
environment that knows how to instantiate such runtime classes (runtime classes
must be autoload-able):
class RuntimeLoader implements \Twig\RuntimeLoader\RuntimeLoaderInterface
{
public function load($class)
{
// implement the logic to create an instance of $class
// and inject its dependencies
// most of the time, it means using your dependency injection container
if ('CustomRuntimeExtension' === $class) {
return new $class(new Rot13Provider());
} else {
// ...
}
}
}
$twig->addRuntimeLoader(new RuntimeLoader());
Note
Twig comes with a PSR-11 compatible runtime loader
(\Twig\RuntimeLoader\ContainerRuntimeLoader
).
It is now possible to move the runtime logic to a new
CustomRuntimeExtension
class and use it directly in the extension:
class CustomRuntimeExtension
{
private $rot13Provider;
public function __construct($rot13Provider)
{
$this->rot13Provider = $rot13Provider;
}
public function rot13($value)
{
return $this->rot13Provider->rot13($value);
}
}
class CustomTwigExtension extends \Twig\Extension\AbstractExtension
{
public function getFunctions()
{
return [
new \Twig\TwigFunction('rot13', ['CustomRuntimeExtension', 'rot13']),
// or
new \Twig\TwigFunction('rot13', 'CustomRuntimeExtension::rot13'),
];
}
}
Testing an Extension¶
Functional Tests¶
You can create functional tests for extensions by creating the following file structure in your test directory:
Fixtures/
filters/
lower.test
upper.test
functions/
date.test
format.test
tags/
for.test
if.test
IntegrationTest.php
The IntegrationTest.php
file should look like this:
namespace Project\Tests;
use Twig\Test\IntegrationTestCase;
class IntegrationTest extends IntegrationTestCase
{
public function getExtensions()
{
return [
new CustomTwigExtension1(),
new CustomTwigExtension2(),
];
}
public function getFixturesDir()
{
return __DIR__.'/Fixtures/';
}
}
Fixtures examples can be found within the Twig repository tests/Twig/Fixtures directory.
Node Tests¶
Testing the node visitors can be complex, so extend your test cases from
\Twig\Test\NodeTestCase
. Examples can be found in the Twig repository
tests/Twig/Node directory.