RFR: 8343306: javac is failing to determine if a class and a sealed interface are disjoint [v6]

[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

Vicente Romero has updated the pull request incrementally with one additional commit since the last revision:

  addressing review comments

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/21794/files
  - new: https://git.openjdk.org/jdk/pull/21794/files/4838a140..d88da991

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21794&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21794&range=04-05

  Stats: 3 lines in 1 file changed: 0 ins; 1 del; 2 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