RFR: 8306729: Add nominal descriptors of modules and packages to Constants API [v3]

[ExE Boss]

On Mon, 24 Apr 2023 16:26:02 GMT, Adam Sotona <asotona at openjdk.org> wrote:

>> Constants API already provides models for all loadable constants to help programs manipulating class files and modelling bytecode instructions. However no models of module and package constants are provided by Constants API. Every program manipulating class files must implement own models and validation of modules and packages constants.
>> 
>> This pul request adds `java.lang.constant.ModuleDesc` and `java.lang.constant.PackageDesc` to the Constants API. 
>> 
>> Classfile API will follow up and remove its internal implementations of `PackageDesc` and `ModuleDesc`. 
>> 
>> Please review this pull request and attached CSR.
>> 
>> Thank you,
>> Adam
>
> Adam Sotona has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Doc fixes + added null and empty tests

Note that other `*Impl` classes in `java.lang.constant` perform validation in their constructors and provide custom `toString()` formatting and they also don’t use records.

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PR Comment: https://git.openjdk.org/jdk/pull/13615#issuecomment-1520483426