How to var_dump variables in twig templates?

Question

View layer pattern where you only present what you have been given is fine and all, but how do you know what is available? Is there a \"list all defined variables\" function

Answer 1

The complete recipe here for quicker reference (note that all the steps are mandatory):

1) when instantiating Twig, pass the debug option

$twig = new Twig_Environment(
$loader, ['debug'=>true, 'cache'=>false, /*other options */]
);

2) add the debug extension

$twig->addExtension(new \Twig_Extension_Debug());

3) Use it like @Hazarapet Tunanyan pointed out

{{ dump(MyVar) }}

or

{{ dump() }}

or

{{ dump(MyObject.MyPropertyName) }}