No error reported for overriding a method and changing an optional parameter default value

[natebosch]

From @eernstg on an internal thread discussing default parameter values.

That shouldn't actually happen, due to the following snippet in the spec: It is a compile-time error if an instance method $m_1$ overrides an instance member $m_2$, the signature of $m_2$ explicitly specifies a default value for a formal parameter $p$, and the signature of $m_1$ implies a different default value for $p$.

Neither the CFE produce an error or warning for this case.

class A {
  void doStuff([int a = 1]) {
    print(a);
  }
}

class B implements A {
  void doStuff([int a = 2]) {
    print(a);
  }
}

void main() {
  A().doStuff();
  B().doStuff();
}

It's likely very breaking to change the tool behavior.

cc @leafpetersen @dgrove

[leafpetersen]

Duplicate of #27476 .