Following #7334 we noticed that our event sources were no longer being cleanup correctly.

Our new style DataSources use Ember Components instead of Ember Proxies and are much more flexible and simpler to use. The main difference being DataSources automatically clean up when they are removed from the page or removed from display (depending if they use loading="lazy" or not)

This uses DataSources in the ACLs area, mainly to load in datacenters in the forms/modals where we use them - and is partly where the idea for IntersectionObserver backed DataSources came from.

A few more advantages here:

1. We only make additional calls to the datacenters API when you open the 'Scoped by datacenters' options, if you never open it we don't make the call.
2. Our policy/role selector components are now backed by blocking queries. If you add a policy or role elsewhere, it will immediately pop-in to the policy/role select menu.
3. Our Datasource/Blocking query support keeps BlockingQueries open until they time out, or we max out our HTTP request restriction. That means they are reused between different instances of the same component in a page, or potentially across pages. This makes for instantaneous loading in some areas.

There is one place where we continue to use our old style EventSources, which we plan to swap out for our new <DataSink /> component further down the line.

We unfortunately and very reluctantly commented out an assertion in a test here. The assertion depends on the DataSource being within the viewport, which you can never guarantee in our test runner (due to skipped tests and size of the window etc etc).

We tried a few methods to improve this mainly around automatically scrolling to about to be clicked dom elements - following the thinking that in order to click something in must first be in the viewport. In the end we decided that this wasn't the right way to solve the problem, and it would be better to somehow provide mockable functionality for dom.isInViewport, and potentially a test step to 'pretend' that a DataSource is in the viewport.

The latter approach probably needs more in-depth work and before that, thinking through properly. So we went with the comment in order to move forwards and come back at a later date 😿