RFR: 8343306: javac is failing to determine disjoint-ness between a class and a sealed interface

[Vicente Romero]

For code like:


class Test {
    sealed interface I permits C1 {}
    non-sealed class C1 implements I {}
    class C2 extends C1 {}
    class C3 {}
    I m(int s, C3 c3) {
        I i = (I)c3;
    }
}

javac is failing to issue an error and accepts this code. The spec is clear stating that code like this should be rejected. See:

5.1.6.1 Allowed Narrowing Reference Conversion:

• A class named C is disjoint from an interface named I if (i) it is not the case that
  C <: I , and (ii) one of the following cases applies:
  – C is freely extensible (§8.1.1.2), and I is sealed , and C is disjoint from all of
  the permitted direct subclasses and subinterfaces of I .

and just below it continues:
• A class named C is disjoint from another class named D if (i) it is not the case
that C <: D , and (ii) it is not the case that D <: C .

so here we have the `C3` is a freely extensible class and interface `I` is sealed and `C3` is disjoint from `C1` which is is the permitted subclass of interface `I`

This PR should sync javac with the spec

TIA

-------------

Commit messages:
 - 8343306: javac is failing to determine disjoint-ness between a class and a sealed interface

Changes: https://git.openjdk.org/jdk/pull/21794/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21794&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8343306
  Stats: 70 lines in 2 files changed: 54 ins; 5 del; 11 mod
  Patch: https://git.openjdk.org/jdk/pull/21794.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21794/head:pull/21794

PR: https://git.openjdk.org/jdk/pull/21794