Sometimes; but there are also a bunch of "foo2nix" tools which can generate "packages" (individually, or sets of inter-dependent definitions) from other formats

Sometimes; but there are also a bunch of "foo2nix" tools which can generate "packages" (individually, or sets of inter-dependent definitions) from other formats[0]. It's basically just generating (parameterised/overridable) "lock files". That's how Nixpkgs can contains massive collections like haskellPackages, pythonPackages, nodePackages, etc. (plus all the various copies with different compilers/interpreters/flags/etc., thanks to the overriding). It can still require some manual tweaking[1], but CI makes that easier, e.g. translate a few thousand definitions; send to CI; mark all those which fail to build as broken. [0] Actually, they generate functions which return derivations; Nix doesn't have a concept of "package", although the term gets thrown around informally. [1] Since those other formats are woefully inadequate at representing dependencies; not just the required compilers/interpreters themselves, but especially stuff like third-party C libraries, binaries that are assumed to be in $PATH, etc. PS: Those "foo2nix" tools don't need to be manually invoked; they can just be another derivation, whose result gets imported (via the import-from-derivation feature). That's how I tend to manage JVM projects (using mvn2nix).