"jar" tool and and reproducible builds - how?

[Danny Milosavljevic <dannym@scratchpost.org>]

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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.

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(define-module (wip nesc)
  #:use-module ((guix licenses) #:prefix license:)
  #:use-module (guix build-system gnu)
  #:use-module (guix download)
  #:use-module (guix packages)
  #:use-module (gnu packages compression)
  #:use-module (gnu packages java)
  #:use-module (gnu packages perl))

(define-public nesc
  (package
    (name "nesc")
    (version "1.3.4")
    (source (origin
              (method url-fetch)
              (uri (string-append "mirror://sourceforge/nescc/nescc/v" version
                                  "/nesc-" version ".tar.gz"))
              (sha256
               (base32
                "0n4mjnm6q96s8pkdq2n9z6cxf5xpy2386cfn30wm4if9gdwhc3w7"))))
    (build-system gnu-build-system)
    (native-inputs
     `(("icedtea" ,icedtea "jdk") ; for tools/java
       ("perl" ,perl)
       ("zip" ,zip)))
    (arguments
     `(#:phases
       (modify-phases %standard-phases
         (add-after 'unpack 'make-jar-reproducible
           (lambda _
             ;; Make JAR file "lib/ncc/nesc.jar" reproducible.
             ;(substitute* "tools/Makefile.in"
             ; ((" jar") " zip -0 -X META-INF/MANIFEST.MF "))
             (substitute* "tools/Makefile.in"
              ((" jar cf \\.\\./nesc.jar")
               " zip -0 -X ../nesc.jar META-INF/MANIFEST.MF "))
             #t)))))
    (synopsis "nesc compiler")
    (description "This package provides a C-like programming language with
small extensions to C, notably a module system (including interfaces),
concurrency and platform-independent networking.")
    (home-page "http://nescc.sourceforge.net/")
    (license license:gpl2)))

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