Magento – How to get the list of applied filters using getActiveFilters

You can do this with the layer resolver (Magento\Catalog\Model\Layer\Resolver). Example code:

public function __construct(
    \Magento\Catalog\Model\Layer\Resolver $layerResolver
)
{
    $this->layerResolver = $layerResolver;
    $layer = $this->layerResolver->get();
    $activeFilters = $layer->getState()->getFilters();
}

Edit:

A small sidenote to those who might concern: you can only get the state after \Magento\Catalog\Controller\Category\View::execute() has already created the state. Otherwise you get a Catalog Layer has been already created runtime exception.

I found the answer for this. (I think) While it makes sense at some level. The flow is kinda messed up. Here it goes:

As I stated in my question the collection used to display the products is a descendant of Magento\CatalogSearch\Model\ResourceModel\Fulltext\Collection that uses a SearchCriteriaBuilder to perform the actual search.

Still when debugging the actual display of the products I could not find any place where the filters were added. But in the _renderFiltersBefore() (method that is called before loading the collection) when the searchCriteriaBuilder was retrieved the filters were already there.

The searchCriteriaBuilder is retrieved using the objectManager::get() which implements a singleton pattern.

Long story short. The same collection(object type not instance) is used for the navigation block. And when rendering it the filters are applied here Magento\LayeredNavigation\Block\Navigation::_prepareLayout()

This are two separate blocks, working with different instances. But because of the singleton approach in retrieving the searchCriteriaBuilder when the ListProduct block loads the collection the filters are already set.

Basically what they've done (from what I can tell) is coupled the shit out of this two blocks.

1. The layered navigation block is rendered and here the filters are applied.
2. When rendering the Product List they "know" that the filters were already applied and go ahead with loading the collection.

I find this to be messed up on so many levels. If someone can prove me wrong. Please do.