RFR: 8356941: AbstractMethodError in HotSpot Due to Incorrect Handling of Private Method [v3]

[Dan Heidinga]

On Fri, 18 Jul 2025 13:53:55 GMT, Dan Heidinga <heidinga at openjdk.org> wrote:

>> David Holmes has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Revert "Additional logging to identify the problem"
>>   
>>   This reverts commit 60871844d32cbc58ea97b2186a2758e85613afa4.
>
> src/hotspot/share/classfile/defaultMethods.cpp line 667:
> 
>> 665:         if (!already_in_vtable_slots(slots, m)) {
>> 666:           Method* impl = klass->lookup_method(m->name(), m->signature());
>> 667:           if (impl == nullptr || impl->is_overpass() || impl->is_static() || impl->is_private()) {
> 
> Trying to capture your and Coleen's discussion in a comment.  Does this correctly cover the gist of the discussion?
> 
> Suggestion:
> 
>          // Unless the klass provides a non-static public or package-private method for this name
>          // & sig combo, we need to add the EmptyVtableSlot so default method processing finds
>          // the correct candidate to fill in the slot later.
>           if (impl == nullptr || impl->is_overpass() || impl->is_static() || impl->is_private()) {

Alternatively, this same series of checks occurs in `FindMethodsByErasedSig::visit()` with a long comment there about the set of possible methods.  Is it worth replacing both sets of checks with a helper method that encapsulates the set of decisions?  


// Private interface methods are not candidates for default methods.
// invokespecial to private interface methods doesn't use default method logic.
// Private class methods are not candidates for default methods.
// Private methods do not override default methods, so need to perform
// default method inheritance without including private methods.
// The overpasses are your supertypes' errors, we do not include them.
static bool is_not_excluded_method(Method* m) {
    if (m != nullptr && !m->is_static() && !m->is_overpass() && !m->is_private()) {
       return true;
    }
    return false;
}


The name isn't great - feel free to replace with something better - but the idea is to capture the requirements in one place

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PR Review Comment: https://git.openjdk.org/jdk/pull/26302#discussion_r2216148094