Proposal: #NonHierarchicalLayers

[mark.reinhold at oracle.com]

2016/12/8 5:46:24 -0800, david.lloyd at redhat.com:
> On 12/07/2016 05:41 PM, mark.reinhold at oracle.com wrote:
>> ...
>> 
>> Could you please describe here, in plain text, what further methods you
>> think you need?  For IP clarity any material you want this EG to consider
>> must be posted to this list or to related OpenJDK infrastructure.
>> 
>> It'd be fine to discuss specific code patches on jigsaw-dev, but again
>> you'd need to include it directly rather than point to GitHub.  This is
>> a design issue, though, so it's probably best to discuss it here first.
> 
> Sure.  I've added the following methods to Layer.Controller:
> 
> public Controller addPackage(Module source, String pn) { ... }
> public Controller addOpens(Module source, String pn, Module target) { ... }
> public Controller addOpensToAll(Module source, String pn) { ... }
> public Controller addOpensToAllUnnamed(Module source, String pn) { ... }
> public Controller addExports(Module source, String pn, Module target) { 
> ... }
> public Controller addExportsToAll(Module source, String pn) { ... }
> public Controller addExportsToAllUnnamed(Module source, String pn) { ... }
> public Controller addUses(Module source, Class<?> service) { ... }

Can you explain exactly why you need all these methods?

I can see why you might need the qualified `addExports` method, akin
to the existing `addOpens` method, if you're doing some form of module
resolution on your own that's somehow taking named layers, or whatever,
into account.

The `add{Opens,Exports}ToAll` variants shouldn't be needed since you can
just include unqualified `open` and `exports` directives in the module
descriptor that you're going to build anyway.  That has the additional
benefit of making the exports apparent to the JPMS resolver so that JPMS
modules can resolve against your modules, whereas invoking these methods
wouldn't do that.

The `addPackage` method is problematic, in part since it's quite slow
(at least in HotSpot, where we've optimized for the common case of the
set of packages in a module never changing).  Can't you compute the set
of packages in a module at the time you create the descriptor?

- Mark