CFE exhuastiveness checker confused by object patterns with private getter names

[stereotype441]

The following program is accepted by the analyzer but rejected by the CFE:

sealed class B {}

class C extends B {
  final int _i;

  C(this._i);
}

f(B b) {
  switch (b) {
    case C(:var _i):
      print('C($_i)');
  }
}

main() {
  f(C(0));
}

The CFE's error message is:

../../tmp/proj/test.dart:10:11: Error: The type 'B' is not exhaustively matched by the switch cases since it doesn't match 'C(_i: Object())'.
 - 'B' is from '../../tmp/proj/test.dart'.
Try adding a default case or cases that match 'C(_i: Object())'.
  switch (b) {
          ^

I believe the analyzer is correct. The switch should be considered exhaustive.

I suspect the problem has to do with the fact that the getter _i is private. If I rename it to i, both the analyzer and the CFE accept the program.

This is probably a severe enough issue that we'll want to cherry-pick a fix to the stable branch.
CC @johnniwinther

[leafpetersen]

This is probably worth considering for a cherry pick if we can get it fixed promptly.