On Mon, 8 Jan 2024 22:29:47 GMT, Joe Darcy <da...@openjdk.org> wrote:
>>> Since it doesn't seem possible to do so, I did not attempt to relay
>>> "non-sealed" information in this PR :-)
>>
>> Naively, I thought that something like this is possible _in principle_; I
>> might be mistaken though:
>>
>> diff --git a/src/java.base/share/classes/java/lang/Class.java
>> b/src/java.base/share/classes/java/lang/Class.java
>> index 851d65d06ad..014845860d0 100644
>> --- a/src/java.base/share/classes/java/lang/Class.java
>> +++ b/src/java.base/share/classes/java/lang/Class.java
>> @@ -4771,6 +4771,30 @@ public boolean isSealed() {
>> return getPermittedSubclasses() != null;
>> }
>>
>> + private boolean isNonSealed() {
>> + if (isSealed())
>> + return false;
>> + if (!isInterface() && Modifier.isFinal(getModifiers())) {
>> + // unlike interface, class can be final
>> + return false;
>> + }
>> + // if an ancestor is sealed, this class can either be non-sealed or
>> final
>> + return hasSealedAncestor(this);
>> + }
>> +
>> + private boolean hasSealedAncestor(Class<?> clazz) {
>> + var superclass = clazz.getSuperclass();
>> + if (superclass != null) {
>> + if (superclass.isSealed() || hasSealedAncestor(superclass))
>> + return true;
>> + }
>> + for (var superinterface : clazz.getInterfaces()) {
>> + if (superinterface.isSealed() ||
>> hasSealedAncestor(superinterface))
>> + return true;
>> + }
>> + return false;
>> + }
>> +
>> private native Class<?>[] getPermittedSubclasses0();
>>
>> /*
>
>> Thanks @pavelrappo; I'll explore incorporating functionality like this into
>> the PR, probably next week.
>
> Pushed an initial cut of non-sealing support; will add more test cases later.
Thanks for including `non-sealed`, Joe.
Regarding your implementation: you are right that only the direct superclass
and direct superinterfaces need to be explored for being `sealed`. No need to
explore the full ancestry. So, recursion in my [initial proposal] was
superfluous.
That said, I have a question on [JLS 8.1.1.2], which you copied as inline
commentary:
> It is a compile-time error if a class is declared non-sealed but has neither
> a sealed direct superclass nor a sealed direct superinterface.
>
> Thus, a subclass of a non-sealed class cannot itself be declared non-sealed.
I wonder if it can be clarified to account for hierarchies where a `non-sealed`
class or `non-sealed` interface has a `non-sealed` direct superinterface, or a
`non-sealed` class has a `non-sealed` direct superclass.
For example:
sealed interface A permits B { }
sealed interface I permits X { }
non-sealed interface B extends A { }
non-sealed interface X extends B, I { }
and
sealed class A permits B { }
sealed interface I permits C { }
non-sealed class B extends A { }
non-sealed class C extends B implements I { }
(CC'ing @GavinBierman)
[initial proposal]:
https://github.com/openjdk/jdk/pull/17239#discussion_r1440867004
[JLS 8.1.1.2]:
https://docs.oracle.com/javase/specs/jls/se21/html/jls-8.html#jls-8.1.1.2
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/17239#discussion_r1446243516
