"jar" tool and and reproducible builds - how?

[Danny Milosavljevic]

Hi,

I'm trying to package nesc which has some small tools written in Java.
It compiles them using "javac" and then packs the result using "jar".

If I want

  guix build --rounds=2 nesc

to pass, how do I best proceed?

I tried

             (substitute* "tools/Makefile.in"
              ((" jar cf \\.\\./nesc.jar")
               " zip -0 -X ../nesc.jar META-INF/MANIFEST.MF "))

but that doesn't seem to be enough.

WIP attached.

Furthermore, I think it would be nice to patch our "jar" tool in icedtea:jdk
so that it provides an option to disable timestamps (not put the timestamp
field into the generated ZIP file in the first place).  I've thus unpacked
icedtea but I can't find where the source code to "jar" is.

nesc.scm
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pgppj5PbPOdDV.pgp
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