RFR: 8343306: javac is failing to determine disjoint-ness between a class and a sealed interface [v2]

[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 with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

 - Merge branch 'master' into JDK-8343306
 - 8343306: javac is failing to determine disjoint-ness between a class and a sealed interface

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/21794/files
  - new: https://git.openjdk.org/jdk/pull/21794/files/38f0de17..9dd1430f

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21794&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21794&range=00-01

  Stats: 2279 lines in 296 files changed: 932 ins; 369 del; 978 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