java -modulepath

[Alan Bateman]

A while back I started looking into supporting "exploded modules". Lots 
of things going on (jdk7 mostly) but I've found a few cycles to do a bit 
more on this so here's a brief status update.

The main update since the first prototype is that the startup has 
improved greatly (as expected) after switching to PathContext and 
generating the path-base configuration at startup. Native libraries are 
now supported if deployed into a -bin tree that mirrors the modulepath. 
So if javac compiles a module "gus" to -d mymodules (mymodules/gus/**) 
then gus's native libraries are loaded from mymodules-bin/gus/lib. 
Clearly any convention would need to be agreed but this one is easy to 
understand. It would be easy to update jpkg and jmod to understand this 
convention when creating packages or installing from a modules directory.

One of the goals with this is to use it in the JDK build so that we can 
move away from the post-processing approach that we have in the jigsaw 
build now. To that end, both module and legacy modes have been updated 
to allow the JDK classes be in a module path structure. This should 
allow us to create the equivalent of the JDK's "make all" where the 
classes are compiled into a classes tree today, and a modules tree in 
the future. A "make images" builds the JDK image including rt.jar today, 
in the future it could create the modules image, installing the JDK 
modules into the module library. This will all require coordination with 
the other build changes going into jdk8 but a reasonable direction to 
take as it makes incremental building very simple and fast (and 
incremental builds are really important when working on the JDK).

Mandy recently published the runtime changes to support the 
ModuleExports attribute. I've done an initial merge with her patch in a 
side forest and added code to check that a type supplied by a remote 
context is exported. Reexporting is working too although I need to do 
more testing on this to verify the semantics. Once I've done that and do 
a bit more clean-up then I'll send our a new webrev for review.

-Alan.