RFR (XS): 8148044: Remove Enum[0] constants from EnumSet and EnumMap

[Roger Riggs]

Hi Claes,

I'm not sure it helps much, but making the ZERO_LENGTH_ENUM_ARRAY 
package-private
(instead of private) will eliminate the need for the accessor.  It is 
not mutable so there's no extra risk.

Roger


On 1/22/2016 10:44 AM, Claes Redestad wrote:
>
>
> On 2016-01-22 15:22, Chris Hegarty wrote:
>> Claes,
>>
>> On 22/01/16 12:07, Claes Redestad wrote:
>>> On 2016-01-22 12:56, Claes Redestad wrote:
>>>> On 2016-01-22 12:53, Alan Bateman wrote:
>>
>>>>> On 22/01/2016 11:34, Claes Redestad wrote:
>>>>>> :
>>>>>> During testing I discovered that EnumSet was missing a
>>>>>> serialVersionUID, which needs to be added.
>>>>> I assume this is not needed, it already has:
>>>>>
>>>>> @SuppressWarnings("serial") // No serialVersionUID due to usage of
>>>>> serial proxy pattern
>>>>
>>>> That's odd.. there's a jtreg test that fails if I don't explicitly add
>>>> the serialVersionUID (that's where I got the actual UID from). I'll
>>>> investigate.
>>>
>>> Right...  java/util/EnumSet/BogusEnumSet.java fails, which is an
>>> explicit test to verify a corrupt EnumSet doesn't deserialize properly:
>>
>> Hmmm... this would indicate that the changes you have made has
>> affected the serial version UID automatically generated. I'm not
>> sure why removing a 'private static' field would do this. Is it
>> possible that you ran into this during development, but it is
>> not actually necessary with the final changes?
>
>> This test is a little fragile, but should be ok.
>>
>>> It would seem the assessment that serialVersionUID is not needed when
>>> using the serial proxy pattern might be misguided (or is this a bug in
>>> ObjectInputStream)?
>>
>> It is debate-able whether this is a test bug or not. But I think
>> we should not change the serialVersionUID for this class, whether
>> truly Serializable or not. Even though in practice it is not all
>> that useful.
>>
>> Can you please revert the serialization parts of the change, and
>> rerun the test? To see if still passes or fails.
>
> I backed out the serial version UID change and reran the test, same 
> thing.
>
> I dug deeper, as this is a bit vexxing...
>
> While a static field does not in and of itself cause the generated UID 
> to change,
> the private ZERO_LENGTH_ENUM_ARRAY is being accessed from 
> SerializationProxy
> class, thus javac generates a package-private synthetic method 
> (access$000) which
> will be accounted for when generating serialVersionUID. That's 
> unfortunate.
>
> I ran a few experiments to confirm this:
>
> - Adding a package-private static method to EnumSet makes the test fail
> - Adding any static field and the test keep passing
>
> So it seems our options here are limited.
>
> Thanks!
>
> /Claes