If a build A depends on a derivation that is the top-level derivation of some build B, then we should process B before A (meaning we shouldn't make the derivation runnable before B has been added). Otherwise, the derivation will be "accounted" to A rather than B (so the build step will show up in the wrong build).
To start hacking on Hydra, run:
$ ./dev-shell
$ ./configure $configureFlags --prefix=/opt/hydra
$ make
$ make install
Or, if you just want to build from source (on x86_64-linux):
$ nix-build -A build.x86_64-linux release.nix
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