RFR: 8345911: Enhance error message when IncompatibleClassChangeError is thrown for sealed class loading failures [v4]

[David Holmes]

On Fri, 13 Dec 2024 12:52:36 GMT, Alan Bateman <alanb at openjdk.org> wrote:

>> David Holmes has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Update messages per feedback from Alan
>
> src/hotspot/share/oops/instanceKlass.cpp line 246:
> 
>> 244:              this->external_name(), this->package() != nullptr ? this->package()->name()->as_C_string() : "unnamed",
>> 245:              this->module()->loader_data()->loader_name_and_id());
>> 246:     log_trace(class, sealed)(" - %s", ss.as_string());
> 
> I'm a bit puzzled by the check so I'm not commenting on the log/exception message just yet.
> 
> If the super class (this) is in an unnamed module then the permitted subclass (k) must be in the same package.
> 
> If the super class is in a named module then permitted subclass can be in a different package but both need to be public in order.
> 
> I'm just trying to see how this maps to the check because it doesn't appear to take named vs. unnamed module into account, e.g. the subclass k might be public but in a different package of the same unnamed module. It's possible that I've mis-read this but it to goes to what the exception message is for these cases.

Those are not the rules in JVMS (at least not obviously so). We get ICCE if any of the following are violated:

- The superclass is in a different run-time module than C (§5.3.6).
- C does not have its ACC_PUBLIC flag set (§4.1) and the superclass is in a different run-time package than C (§5.3).
- No entry in the classes array of the superclass's PermittedSubclasses attribute refers to a class or interface with the name N. 

We already determined both classes are in the same module, so now we just do the public/same-package check. Whether the module is un-named or not doesn't come into it.

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

PR Review Comment: https://git.openjdk.org/jdk/pull/22703#discussion_r1884538725