When promoting fields, in order to avoid unsoundness, we need to
distinguish between field accesses performed through `super` and field
accesses performed through `this`. Otherwise, a user could do
something like this:
class B {
final int? _i;
B(this.i);
}
class C extends B {
final int? _i;
C(this._i, int? superI) : super(superI);
int f() {
if (super._i != null) {
return this._i; // UNSOUND: `this._i` could be `null`
}
}
}
To avoid this problem, flow analysis now uses separate promotion keys
for `super` and `this`, so that promoting a variable through `this`
leaves it unpromoted when accessed via `super`, and vice versa.
Note that in principle the implementations could inspect the enclosing
class, and only distinguish `this.` and `super.` accesses in the case
where it contains a declaration matching the field name. But doing so
would carry a performance and implementation complexity cost, and
would confer very little real-world benefit (since in practice users
don't mix `this.` and `super.` accesses and expect them to refer to
the same field).
Fixes#50138.
Bug: https://github.com/dart-lang/sdk/issues/50138
Change-Id: Ia0fd79b5ed7649d23a28efcbffb59b4c9ad63f70
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/304364
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>
Paul Berry
70e7adff19