NNBD: Dart does not throw compile error when declare incorrectly super bounded to non-null Object variable.

[iarkh]

Dart VM version: 2.9.0-16.0.dev (dev) (Tue Jun 16 10:35:10 2020 +0200) on "windows_x64"

Here is a source code example:

class A<T extends A<T>> {}

main() {
  A<Object?> a1;
  A<Object>  a2;

  A<A<Object?>> a3;
  A<A<Object>>  a4;
}

Dart passes with this with nnbd enabled.

Object is not a top type with null-safety enabled, so actually dart should throw a compile error for a2 and a4 here.

See also Issue #42415.

[lrhn]

Correct, Object is no longer a top type, so it isn't allowed as a type argument in super-bounded types.

[johnniwinther]

Likely related to #41684