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by tadfisher
2 days ago
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The systemd issue in particular is something I've experienced. nixpkgs does not split systemd into many packages, so everything that needs udev, libsystemd, etc depends on it, so replacing systemd via an overlay will cause a mass rebuild. The trick is to patch systemd and refer to your patched version separately, e.g. with a pkgs.writeShellScript that calls ${systemd-patched}/bin/patched-binary. |
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I mean, generally when you patch things, you want all dependents to use the patched version. It's just irksome that you know the change you made strictly speaking doesn't need a rebuild of dependents, but nix will still require it in the interest of ensuring reproducibility. Just wish there were an established expert-mode I-know-this-may-break-things way to have a modified derivation act as a drop-in replacement of a particular package/digest.
For example, it would be neat to have derivation foo.nix, from which the digest is calculated. Then, have the system check for a mod/foo.nix or similar path which would be a function that can modify the derivation without having the digest be recalculated on the result. Or maybe this could be done by having a function calcDigest, which sets the digest of a derivation and the system can simply not set the field when it's already been set. This to allow further changes while being treated as if changes haven't been made.