extension_override_with_cascade

Extension overrides have no value so they can't be used as the receiver of a cascade expression.

The analyzer produces this diagnostic when an extension override is used as the receiver of a cascade expression. The value of a cascade expression e..m is the value of the receiver e, but extension overrides aren't expressions and don't have a value.

The following code produces this diagnostic because E(3) isn't an expression:

extension E on int {
  void m() {}
}
f() {
  E(3)..m();
}

Use . rather than ..:

extension E on int {
  void m() {}
}
f() {
  E(3).m();
}

If there are multiple cascaded accesses, you'll need to duplicate the extension override for each one.