Adding a default filter to discussions breaks a few things

[iPurpl3x]

Current Behavior

When adding a filter to the api/discussions endpoint that is activated by default (including when on /all and with default sort), then things like "Hide from All Discussions" in flarum/tags or the entire flarum/sticky logic just get ignored because there is an active filter.

I suppose the code that has been written makes sense because in most cases when you are on /all and have the default sort selected, there are no filters active. But in my use-case there is, so those extensions (tags & sticky) are broken. Maybe there are other things that are broken as well that I am not yet aware of...

As a reference, here are the lines of code that are making things break, because they are hard-coded to check if there is an active filter, and if there is the rest of the logic is skipped...

• framework/extensions/sticky/src/PinStickiedDiscussionsToTop.php

  Line 27 in 05f80b7

  if ($count = count($filters)) {

• framework/extensions/tags/src/Filter/HideHiddenTagsFromAllDiscussionsPage.php

  Line 20 in 379c063

  if (count($filter->getActiveFilters()) > 0) {

Steps to Reproduce

1. Add a filter with an extension
2. Make that this filter is active by default
3. See broken sticky and tags behaviour

Expected Behavior

Tags and Sticky should work if there is a filter activated by default

Environment

• Flarum version: 1.5.0
• PHP version: 8.0.x

Possible Solution

A possible solution could be to add an extender that allows extensions to blacklist their filters so that they don't get counted when checking if there are active filters.

[SychO9]

can you please give an example use case for such a filter?
I'm thinking if a filter is meant to always be applied, why not make it a mutator instead? Or how do you decide when it is and isn't applied?

[iPurpl3x]

@SychO9 an example would be fof/discussion-language. Depending on the settings, there are cases where the discussions are filtered by the user language.