nixpkgs/pkgs/lib/customisation.nix

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let lib = import ./default.nix;
inherit (builtins) getAttr attrNames isFunction;
in
rec {
/* `overrideDerivation drv f' takes a derivation (i.e., the result
of a call to the builtin function `derivation') and returns a new
derivation in which the attributes of the original are overriden
according to the function `f'. The function `f' is called with
the original derivation attributes.
`overrideDerivation' allows certain "ad-hoc" customisation
scenarios (e.g. in ~/.nixpkgs/config.nix). For instance, if you
want to "patch" the derivation returned by a package function in
Nixpkgs to build another version than what the function itself
provides, you can do something like this:
mySed = overrideDerivation pkgs.gnused (oldAttrs: {
name = "sed-4.2.2-pre";
src = fetchurl {
url = ftp://alpha.gnu.org/gnu/sed/sed-4.2.2-pre.tar.bz2;
sha256 = "11nq06d131y4wmf3drm0yk502d2xc6n5qy82cg88rb9nqd2lj41k";
};
patches = [];
});
For another application, see build-support/vm, where this
function is used to build arbitrary derivations inside a QEMU
virtual machine. */
overrideDerivation = drv: f:
let
# Filter out special attributes.
drop = ["meta" "passthru" "outPath" "drvPath" "hostDrv" "buildDrv" "type" "override" "deepOverride" "origArgs"]
# also drop functions such as .merge .override etc
++ lib.filter (n: isFunction (getAttr n drv)) (attrNames drv);
attrs = removeAttrs drv drop;
newDrv = derivation (attrs // (f drv));
in newDrv //
{ meta = if drv ? meta then drv.meta else {};
passthru = if drv ? passthru then drv.passthru else {};
};
# usage: (you can use override multiple times)
# let d = makeOverridable stdenv.mkDerivation { name = ..; buildInputs; }
# noBuildInputs = d.override { buildInputs = []; }
# additionalBuildInputs = d.override ( args : args // { buildInputs = args.buildInputs ++ [ additional ]; } )
makeOverridable = f: origArgs: f origArgs //
{ override = newArgs:
makeOverridable f (origArgs // (if builtins.isFunction newArgs then newArgs origArgs else newArgs));
deepOverride = newArgs:
makeOverridable f ((lib.mapAttrs (deepOverride newArgs) origArgs) // newArgs);
origArgs = origArgs;
};
deepOverride = newArgs: name: x: if builtins.isAttrs x then (
if x ? deepOverride then (x.deepOverride newArgs) else
if x ? override then (x.override newArgs) else
x) else x;
}