Use case

Exposing the Scroll Controller of a TabBar with isScrollable: true, will let developers apply custom behavior based on the scroll.
In my case, it was necessary to apply a Gradient Mask (Container with LinearGradient in Stack) over the TabBar to indicate to the user that there are more elements out of screen.
Example:

There was already an issue about it, but it has been closed (#64880)

Proposal

It can be made in many ways, two of them can be:

• As a parameter, we can provide our own ScrollController. If null, we can check the presence of a PrimaryScrollController. If null, fallback to the _TabBarScrollController already provided
• Through a key, access to the State of the TabBar, making _scrollController public