The rule for packages in this directory is that they can depend on
nothing but core Dart packages. They can't depend on dart:ui, they
can't depend on any package:, and they can't depend on anything
outside this directory.
Currently they do depend on dart:ui, but only for VoidCallback and
hashValues (and maybe one day hashList and lerpDouble), which
are all intended to be moved out of dart:ui and into dart:core.
See also:
-
https://github.com/dart-lang/sdk/issues/27791 (
VoidCallback) -
https://github.com/dart-lang/sdk/issues/25217 (
hashValues,hashList, andlerpDouble)