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

[Adam Sotona]

On Sat, 11 Mar 2023 17:00:18 GMT, Alan Bateman <alanb at openjdk.org> wrote:

>> `buildModules` is expected to be called with additional packages but instead it's called with all packages including all exported and open packages.   
>> 
>> 
>>     /**
>>      * Build a module descriptor into a byte array.
>>      * @param moduleAttribute the {@code Module} attribute
>>      * @param packages additional module packages
>>      * @param handler a handler that receives a {@link ClassBuilder}
>>      * @return the classfile bytes
>>      */
>>     public static byte[] buildModule(ModuleAttribute moduleAttribute,
>>                                      List<PackageDesc> packages,
>>                                      Consumer<? super ClassBuilder> handler) {
>> 
>> 
>> I checked the implementation that seems to match `@param packages` that expects additional module packages that are not exported nor open.  If it intends to take additional packages, it will need to filter the exported and open packages at the callsite.
>> 
>> Or the `packages` parameter lists all packages that will be used to create `ModulePackages` attribute.  This seems to be easier to understand.
>
> Maybe the variants of Classfile.buildModule need to be looked at again. For the usage here, buildModule(ModuleAttribute, Consumer<? super ClassBuilder>) would be more useful as it would allow all of the additional attributes to be emitted in the handler rather than having buildModule making the decision on whether to emit the ModulePackages attribute.

`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.

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