RFR: 8294962: Convert java.base/jdk.internal.module package to use the Classfile API to modify and write module-info.class [v4]

[Alan Bateman]

On Mon, 13 Mar 2023 13:47:31 GMT, Adam Sotona <asotona at openjdk.org> wrote:

>> `Classfile::buildModule` is a helper method simplifying the major use case - building valid module with minimal user effort and knowledge. It emits `ModulePackages` if there are any packages specified and not exported nor opened. That is the configuration which JVM expects and majority of users are not aware of.
>> Other module-specific attributes can be added in the underlying handler, using `ClassBuilder::with`.
>> 
>> A different building approach can be used in cases (which I would like to know more about) where even `ModulePackages` attribute needs to be "customised" or provided unconditionally. It is always possible to build module as a class using `Classfile::build` from scratch and provide all the attributes manually.
>
> Or another approach for the specific use cases might be to use `Classfile::buildModule` with empty list of packages and then provide custom `ModulePackagesAttribute` to the handler directly.

> `Classfile::buildModule` is a helper method simplifying the major use case - building valid module with minimal user effort and knowledge. It emits `ModulePackages` if there are any packages specified and not exported nor opened. That is the configuration which JVM expects and majority of users are not aware of. 

ModulePackages is a performance optimization. When present, the value is the  set of packages in the module. If not present, the module contents need to be scanned to discover the set of packages. I think it's just a bit too surprising for Classfile::buildModule to emit the ModulePackages attribute sometimes and not others. I think it would be better to change is so that calling it with ModuleAttribute will emit a Module attribute. The overloads that take a Module plus a set of packages can emit a Module + ModulePackage unconditionally.

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PR: https://git.openjdk.org/jdk/pull/11368