[Nix-dev] Referring to a path inside ${out}...in a nix expression

[Bryce L Nordgren]

Apologies if this is another dumb question, but I think I don't know
the proper terms to google.

I'm writing an expression (in nixpkgs) for geonetwork-opensource. This
is now working as a maven build. The thing I'm putting in $out, for
the moment, is the maven repository. This contains all of the *.jar
files that maven had to download in order to compile the webapp, plus
the compiled version of the geonetwork-opensource code, plus the
"warfile", which is more or less a zipfile containing a standardized
directory structure that java servers understand.

I want the nix expression to have the path to the warfile in an
attribute, like so:

stdenv.mkDerivation { .. } :
{
 ...
 warfile = "${out}/repository/big/fat/path/geonetwork-opensource-2.6.4.war"
 ...
}

This is so I can use the attribute later:

...
config.{...}...tomcat.warfile = pkgs.geonetwork.warfile ;
...

How do I accomplish this? Up in the geonetwork expression, the parser
complains that "out" is undefined. As is "geonetwork". As is
"pkgs.geonetwork".

Again, sorry if it's a dumb question.