CFE/analyzer disagreement on set literal type inference

[Pante]

Dart version: 3.11.0
Platform: macOS

The following code snippet that was previously working in Dart 3.10.8 does not compile on Dart 3.11.0.

class Parent {}

class Base implements Parent {}

extension type const MidA._(Parent _) implements Parent {}

extension type const A._(Base _) implements MidA, Base {}

extension type const MidB._(Parent _) implements Parent {}

extension type const B._(Base _) implements MidB, Base {}

void f(Set<Base> s) {}

void main() {
  final Set<A> a = {};
  final Set<B> b = {};

  // OK
  f({...a, ...b});

  // Error: CFE infers Set<Object> while analyzer infers Set<Base>
  final merged = {...a, ...b};
  f(merged);
}

Analyzer infers the correct type:

Error:

lib/src/theme/main.dart:24:5: Error: The argument type 'Set<Object>' can't be assigned to the parameter type 'Set<Base>'.
 - 'Set' is from 'dart:core'.
 - 'Object' is from 'dart:core'.
 - 'Base' is from 'package:forui/src/theme/main.dart' ('lib/src/theme/main.dart').
  f(merged);
    ^

Process finished with exit code 254

[lrhn]

Agree that UP(A, B) should be Base and that var merged = {...a, ...b}; should be a Set<Base>.

The common super-interfaces of A and B are only Object, Parent and Base, with Base being the deepest.

[eernstg]

It should actually be a Set<Parent> because MidA, MidB, and Base are at the same depth, so the deepest level which is a singleton is Parent.

graph BT;
  Object --> ObjectQ["Object?"]
  Parent --> Object
  Base --> Parent
  MidA --> Parent
  MidB --> Parent
  A --> MidA
  A --> Base
  B --> MidB
  B --> Base

Loading

If we have Set<Base> as the context type then {...a, ...b} can be typed as Set<Base>, and that's working.

[lrhn]

It's true that Base has the same depth as MidA and MidB, but I still think UP(A, B) is Base.

The intersection of superinterfaces for A and B shouldn't contain MidA or MidB, because they are not superinterfaces of both types.
The intersection only contains Object, Parent and Base, with Base having the largest depth.

[eernstg]

You're right, it's Base because MidA and MidB aren't shared superinterfaces.