[foreign-abi] RFR: 8253796: Consider making CValueLayout public.

[Jorn Vernee]

On Tue, 29 Sep 2020 16:05:26 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> Hi,
>> 
>> This PR makes CValueLayout a public nested class of CLinker, meant to be extended. To quote the motivation from the JBS
>> issue:
>>> Jextract uses an attribute to attach temporary information to layouts regarding the canonical layout field in CLinker
>>> they correspond to.
>>> But, creating a dynamic constant out of these layouts is a complex process, since we need to recursively filter out
>>> this internal jextract attribute, which requires us to recreate GroupLayouts, SequenceLayouts, FunctionDescriptors, and
>>> ValueLayouts.  It would be easier if we could extend CValueLayout with a custom jextract layout class, which has an
>>> extract field to indicate which CLinker constant they correspond to. In that case e.g. SourceConstantHelper can cast to
>>> this custom class and retrieve this extra field, removing the need to use attributes, and the difficulties associated
>>> with them.
>> 
>> Thanks,
>> Jorn
>
> src/jdk.incubator.foreign/share/classes/jdk/incubator/foreign/CLinker.java line 794:
> 
>> 792:         }
>> 793:
>> 794:         public final Kind kind() {
> 
> Same here - should this exposed?

Yes, kind should be exposed. The classification logic needs to access it, and if we don't expose it it's not possible
to extend this class, since the kind is a constructor argument and we need to call the constructor from the subclass.

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PR: https://git.openjdk.java.net/panama-foreign/pull/359