Hi, > What kinds of attributes are appropriate as passthrough attributes on > a derivation set, and which attributes are appropriate to be written > out to the store in a nix-support file?
passthru attributes are visible in the derivation's attribute set -- i.e. other expressions can see them during the evaluation of Nixpkgs --, but they are not visible to the derivation's builder. In other words, passthru attributes cannot affect the build and thus cannot affect the $out hash of the generated package. This is useful whenever you want to provide additional information about the package to its users within Nixpkgs, but you don't want to rebuild everything whenever that information changes. Normal attributes are available within Nixpkgs the same way as passthru attributes, but they can affect the build, obviously, and thus cannot be changed without triggering a re-compilation of the package and all its dependents. Data that is written to the $out store path isn't readily available during Nixpkgs evaluation, but it's available outside of Nix, i.e. a shell script can source the file and use the information contained inside of it. Files that live inside of $out/nix-support are omitted when a user profile is built, i.e. user profiles never contain that hierarchy. For files that ought to be installed, $out/lib/$name or $out/etc/profile.d/$name might be a better choice. Personally, I've never needed passthru attributes for anything, and I've yet to create some file in $out/nix-support. So far, everything I've wanted to do was possible with either a normal attribute or a normal file somewhere in $out. Your mileage may vary, though. I hope this helps, Peter _______________________________________________ nix-dev mailing list nix-dev@lists.science.uu.nl http://lists.science.uu.nl/mailman/listinfo/nix-dev
