Feature of checking for pattern matching on case changing enums (discussion).

One of the challenges of pattern matching enums is that not all enums are designed for exhaustive pattern matching.

I have written my own annotation that you put on an enum to indicate that you should not rely on exhaustive pattern matching:
https://jstach.io/doc/rainbowgum/current/apidocs/io.jstach.rainbowgum.annotation/io/jstach/rainbowgum/annotation/CaseChanging.html

The idea is to avoid the issue where version one we have

enum MyEnum {
 A,
 B
}

Consumer of library writes

MyEnum e;
switch(e) {
  case A -> ...;
  case B -> ...;
}

And then version 2 a mostly backward compatible version (lets ignore the debate what is a major, minor, etc semver policy and binary vs source compat):

enum MyEnum {
 A,
 B,
 C
}

Then the client will get an unexpected failure for C.

Any way I was going to take a stab on implementing this checker on my own to try to improve my knowledge of the checkerframework and thought I would mention it.

Start by reading the linked CaseChanging annotation and the Java enum examples in the issue. Investigate how the Checker Framework could represent and check this annotation for enum pattern matching; done requires an agreed checker design and defined behavior when a later enum version adds a constant.