[20] Switch statement with record pattern illegally reported as non-exhaustive

[jarthana]

The switch in the following code is rejected by ECJ as not exhaustive:

interface I {}
class Class implements I {}
record Record(I s) {}
public class X1 {
    @SuppressWarnings("preview")
	public void foo(Record exp) {
        switch (exp) {
            case Record(Class s) -> {break;}
        }
    }
}

This is because, as per RecordPattern#isTotalForType() , it is considered to be always false. This method needs consider the record pattern's type as well as the nested patterns' types.

[jarthana]

Since this is still a preview feature in 20 and a standard feature in 21, I would rather we fix this for 21 directly.

Copying @mpalat