OrderedATNConfigSet has bad override of configLookup field

[jakemac53]

See

antlr4/runtime/Dart/lib/src/atn/src/atn_config_set.dart

Line 290 in 47415e3

final configLookup = <ATNConfig>{};

In general, overriding fields is a bad idea in Dart. Both fields exist, but the one on the super class is only accessible through an explicit super.<field> invocation.

In particular in this case, it is much worse since the subclass declares the field as final, it only overrides the getter, and not the setter. So there is a setter still, which assigns to the base class field, which can never be read (except through a super. invocation in the subclass).

In this case, the subclass does try to set the configLookup field, which has no effect, because that field is never read.

[jakemac53]

Note that this causes a failure in DDC when null safety asserts are enabled, dart-lang/sdk#50569. That is technically a compiler bug, but it highlighted this pattern which is almost certainly not doing what was intended.