PHP __LINE__ equivalent for twig - twig

Question

There is a way to get PHP __LINE__ equivalent for Twig?
It's almost impossible to search __LINE__ on Google as exact word...
The purpose is purely for debugging a long twig file containing nested twig code inside a complex Js code, to console.log it.
The version of twig I'm using is 2.12.5.
Thanks

Answer 1

First things first:
As seen in the PHP documentation the (magic) constant will return the current line number of the file.The "problem" here is that twig converts templates to PHP in order to render them.
This means if you were actually were to be able to use __LINE__ inside a template, it would report back the line number from either a temporary PHP file or a cached PHP file, wether you have caching enabled or not.
TLDR: Using __LINE__ inside a template is going to report back "false"/useless information.
However, you can easily extend twig and even introduce new tags which you then can use inside templates. These customs tags allow you to modify/alter the compilation of the template's PHP file.
The interesting part here is that the "compiler" is able to provide your custom tag on which specific line the tag was called.
We can even create a custom tag, register it with twig and let the tag report back the line number in the parsed template.
Step 1 - Create a TokenParser
The TokenParser is responsible for parsing the template and allows you to choose a name for your tag. The code below will be responsible to create a simple, empty tag named line
<?php
namespace MyProject\Base\Twig\TokenParser;
use \MyProject\Base\Twig\Node\Line as LineNode;
class Line extends \Twig_TokenParser {
public function parse(\Twig_Token $token)
{
$this->parser->getStream()->expect(\Twig_Token::BLOCK_END_TYPE);
return new LineNode(new \Twig_Node(), $token->getLine(), $this->getTag());
}
public function getTag()
{
return 'line';
}
}
Step 2 - Create a Node
The Node is responsible for converting the template code to actual PHP code
<?php
namespace MyProject\Base\Twig\Node;
class Line extends \Twig_Node {
public function __construct(\Twig_NodeInterface $body, $lineno, $tag = null) {
parent::__construct(['body' => $body,], array(), $lineno, $tag);
}
public function compile(\Twig_Compiler $compiler) {
$compiler->write('echo '.$this->getLine().';')
->write(PHP_EOL);
}
}
Step 3 - Register the tag with twig
<?php
namespace MyProject\Base\Twig;
class MyProjectTwigExtension extends Twig_Extension {
public function getTokenParsers() {
return [
new \CMS4U\Base\Twig\TokenParser\Line(),
];
}
public function getName() {
return 'MyProjectTwigExtension';
}
}
<?php
$twig->addExtension(new \MyProject\Base\Twig\MyProjectTwigExtension());
If everything is good, you can now use the custom tag {% line %} wherever you like in any template
Foo
Bar
FooBar
Current line number is {% line %} {# 4 #}