Snippets

This page contains some nix script snippets which might be useful.

Adding compiler flags to a package

   optimizeWithFlag = pkg: flag:
     pkg.overrideAttrs (attrs: {
       NIX_CFLAGS_COMPILE = (attrs.NIX_CFLAGS_COMPILE or "") + " ${flag}";
     });

This function can further be used to define the following helpers:

   optimizeWithFlags = pkg: flags: pkgs.lib.foldl' (pkg: flag: optimizeWithFlag pkg flag) pkg flags;

   optimizeForThisHost = pkg: optimizeWithFlags pkg [ "-O3" "-march=native" "-fPIC" ];

   withDebuggingCompiled = pkg: optimizeWithFlag pkg "-DDEBUG";

Overriding callPackage for finding updated upstream packages in own overrides

With this override for the `callPackage` function, one can automatically detect if the upstream package set has a newer version of an locally overridden package:

   callPackage = path: args: let
       override =  super.callPackage path args;
       upstream = optionalAttrs (override ? "name")
         (super.${(parseDrvName override.name).name} or {});
     in if upstream ? "name" &&
           override ? "name" &&
           compareVersions upstream.name override.name != -1
       then
         trace
           "Upstream `${upstream.name}' gets overridden by `${override.name}'."
           override
       else override;
   # Credit to makefu