RFR: 8258411: Move module set configuration from Modules.gmk to conf dir [v2]

[Mandy Chung]

On Tue, 15 Dec 2020 22:47:16 GMT, Mandy Chung <mchung at openjdk.org> wrote:

>> As for `JRE_TOOL_MODULES`, I understand what you mean but it is at least kind of a "sibling" to the others. After all, we use these sets of modules together to form the set of modules for the JRE:
>> 
>> JRE_MODULES += $(filter $(ALL_MODULES), $(BOOT_MODULES) \
>>     $(PLATFORM_MODULES) $(JRE_TOOL_MODULES))
>> 
>> So given that `BOOT_MODULES` and `PLATFORM_MODULE` has a role to play here as well, I think it would be odd *not* to have `JRE_TOOL_MODULES` defined at the same place.
>
> `JRE_TOOL_MODULES` started with more than one modules in JDK 9:
> 
> JRE_TOOL_MODULES += \
>     jdk.jdwp.agent \
>     jdk.pack \
>     jdk.scripting.nashorn.shell \
>     #
> 
> Since only `jdk.jdwp.agent` one module is left for `JRE_TOOL_MODULES`, as you are refactoring this file, I suggest to get rid of `JRE_TOOL_MODULES` and explicitly name `jdk.jdwp.agent` in `JRE_MODULES`.

Do you see a way to get rid of `DOCS_MODULES` but determine this set at build time?  IIRC it was added for expediency for [JDK-8172312](https://bugs.openjdk.java.net/browse/JDK-8172312).   This is the set of JDK (non-Java SE) modules (excluding `jdk.internal.*` modules and `jdk.unsupported` and also platform-specific modules). 

As for the conf file for module to class loader mapping, I actually like one single file `jdk-modules.conf` to enumerate all JDK modules.   Currently it only defines the list of modules defined to boot and platform class loader but excludes any modules defined to application class loaders.  I consider to enumerate all modules in this file and the build can verify if any module is missing.

`module-sets-build.conf` is a bit awkward and I will give more thought on naming ideas.

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PR: https://git.openjdk.java.net/jdk/pull/1781