Hi Ludo,

here's the promised patch to follow up with the code duplication I
introduced in my previous patch.

I tested this by compiling Clojure which uses the Ant build system, and
by compiling clojure-tools-deps-alpha which uses the Clojure build
system. Both of the build systems now call the repack-jar function.

Could you have a look at it please?

A related question:

When I run the following commands after modifying the build systems they
run for quite some time, because they were compiling a ton (the jdk,
jetty) of things.

./pre-inst-env guix build clojure
./pre-inst-env guix build clojure-tools

I guess this is expected, since a change in a build system might affect
all packages being built with it. But I was wondering if there is a way
to force only building the packages specified on the command line. Does
such a thing exists?

I was wondering what is the most efficient way to quickly iterate on
changes to a build system, without recompiling the whole world for that
build system. How would you do that?

Thanks, Roman.