Arnaud B <arnaud.beaudhuin@gmail.com> writes:

> The thing is that I can not debug the build process, even though I use the
> --keep-failed option : I'm not getting a temp build directory
> (/tmp/guix-build-...) as I expect :

This is so because it fails too early, that is, before it builds.

The error is that when using `-f`, guix build _evaluates_ the target
file and builds the _result_.  See `guix build --help`.

The `define-public` does not return a `package`, hence the error.
Simply remove the `define-public` and it should work.

Alternatively, you can place your file in a folder pointed by
GUIX_PACKAGE_PATH, leave the `define-public` and build with `guix build
freefilesync --keep-failed`.

Don't forget that the declared module must match the path, so if you
stick to (gnu packages freefilesync) place the file in
$GUIX_PACKAGE_PATH/gnu/packages/freefilesync.scm.

> One thing to add is that the downloaded source file is not tar.gz file
> format but zip file, perhaps that's part of the problem ?

I think you need

    (native-inputs
     `(("unzip" ,unzip)))

And add the (gnu packages compression) module.

A nit: the package name should be lowercase I think.

Love the description, haha! :)

--
Pierre Neidhardt