Review request: jar tool to transform a plain jar file to a modular jar

[Mandy Chung]

  Updated webrev:
     http://cr.openjdk.java.net/~mchung/jigsaw/webrevs/modularize-jar.01/

To modularize an existing jar file:
1. use 'I' flag to specify the module name

   $ jar ufI astro.jar org.astro at 2.0

   $ jar tvf astro.jar
       0 Tue Aug 30 16:15:04 PDT 2011 META-INF/
     74 Tue Aug 30 16:15:04 PDT 2011 META-INF/MANIFEST.MF
       0 Tue Aug 30 16:15:00 PDT 2011 org/
       0 Tue Aug 30 16:15:00 PDT 2011 org/astro/
  276 Tue Aug 30 16:15:00 PDT 2011 org/astro/World.class
   172 Tue Aug 30 16:21:26 PDT 2011 module-info.class<---- newly generated

2. add module-info.class to the jar file as an input file

   $ jar uf greetings.jar -C modules/com.greetings module-info.class

Installing a modular JAR file in the module library
     $ jmod install greetings.jar astro.jar -L mlib

Run in module mode
     $ java -L mlib -m com.greetings

Details:
The jar tool provides a new option to transform a plain old JAR file
into a modular JAR:
    -I {module-name at version}
       Generate "module-info.class" entry in the JAR file [a]

It is designed to handle simple cases that:
    * requires the default Java platform module [b]
    * exports all public types
    * main entry point as specified in the manifest or in the 'e'
      flag, if any
    * infers the dependencies from 'Class-Path' attribute if it is
      a modular JAR file, and the specific module name of
      that version will be added in the module dependency [c].

The jar tool will determine if the inputfiles include a
"module-info.class" entry that indicates that it is a modular
application [d].  If exists, 'I' flag cannot be specified.

Implementation: I use the classfile library that Jon Gibbons wrote
to generate the module-info.class.  Since Jon will be updating
javac and classfile per the module-info spec [3], I modified
ModuleExport_attribute and ModuleRequires_attribute classes in
a simple way but the right change will come when they are updated
per the proposed spec.

Footnotes:
[a] jarfile name tends to be unnamed or contains '-' character.
     The module name will not be inferred from the jarfile name.
[b] Private and internal APIs in the jdk are not exported.
     If the JAR file depends on any of these APIs and running
     in module mode, this will result in a runtime error.
[c] If the path listed in the 'Class-Path' attribute is not a
     modular JAR, it will simply issue a warning and continue.
     Module dependencies may be incomplete in this case.
[d] If an application has been modularized, module-info.java that
     describes the module definition is placed in the root of the
     source tree and compiled in the same destination directory as
     its classes.

Mandy
[1] 
http://mail.openjdk.java.net/pipermail/jigsaw-dev/2011-August/001452.html