RFR: 8290041: ModuleDescriptor.hashCode is inconsistent

[Joe Darcy]

On 8/9/2022 11:56 PM, Peter Levart wrote:
> On Sun, 7 Aug 2022 08:14:58 GMT, Alan Bateman <alanb at openjdk.org> wrote:
>
>>> Sorry for joining late. I noticed that modsHashCode is a private method and it takes Iterable as a parameter. But everywhere it is called, a Set is passed to it. So why not just calling the set.hashCode() and be done with it? It may be even more optimal in some cases.
>> There's a lot going on here as the hash code is generated at link time and we also want it to be reproducible across builds. We also had a CDS bug with the the way that Enum objects were archived - Ioi has fixed that in JDK 19 so we have one less thing to be concerned about now.
> Ah, I see. Enum.hashCode() is identity hash code. I have been beaten by that in the past and apparently this is a sore point for many. I wonder if it could be changed. Is unstable hashCode (accross JVM instances) a feature here or just unfortunate implementation detail?
>
We've gotten a few issues filed about Enum.hashCode() over the years, 
one more recent one is

     JDK-8050217: Enum.hashCode() should return ordinal value for the 
enum, for better consistency

Current thinking per that issue is the present behavior is more of a 
feature than a bug.

-Joe