nixpkgs/pkgs/build-support/replace-dependency.nix
Shea Levy d1662d7155 Add the replace-dependency build support function.
The use case is to do a deep replacement of a dependency without rebuilding the entire tree.
For example, suppose a security hole is found in glibc and a patch released. Ideally, you'd
just rebuild everything, but that takes time, space, and CPU that you might not have, so in
the mean time you could build a safe version of, say, firefox with:

  firefox-safe = replace-dependency { drv = firefox; old-dependency = glibc; new-dependency = patched-glibc; };

Building firefox-safe will rebuild glibc, but only do a simple copy/string replacement on all other dependencies
of firefox. On my system (MBP 13" mid-2012), after a new glibc had been build building firefox took around 11 seconds.

See the comments in the file for more details.
2013-01-11 14:42:09 -05:00

81 lines
2.8 KiB
Nix

{ runCommand, nix, lib }:
# Replace a single dependency in the requisites tree of drv, propagating
# the change all the way up the tree, without a full rebuild. This can be
# useful, for example, to patch a security hole in libc and still use your
# system safely without rebuilding the world. This should be a short term
# solution, as soon as a rebuild can be done the properly rebuild derivation
# should be used. The old dependency and new dependency MUST have the same-length
# name, and ideally should have close-to-identical directory layout.
#
# Example: safe-firefox = replace-dependency {
# drv = firefox;
# old-dependency = glibc;
# new-dependency = overrideDerivation glibc (attrs: {
# patches = attrs.patches ++ [ ./fix-glibc-hole.patch ];
# });
# };
# This will rebuild glibc with your security patch, then copy over firefox
# (and all of its dependencies) without rebuilding further.
{ drv, old-dependency, new-dependency }:
with lib;
let
references = import (runCommand "references.nix" { exportReferencesGraph = [ "graph" drv ]; } ''
(echo {
while read path
do
echo " \"$path\" = ["
read count
read count
while [ "0" != "$count" ]
do
read ref_path
if [ "$ref_path" != "$path" ]
then
echo " (builtins.storePath $ref_path)"
fi
count=$(($count - 1))
done
echo " ];"
done < graph
echo }) > $out
'').outPath;
discard = builtins.unsafeDiscardStringContext;
old-storepath = builtins.storePath (discard old-dependency.outPath);
references-of = drv: getAttr (discard (toString drv)) references;
depends-on-old = drv: elem old-storepath (references-of drv) ||
any depends-on-old (references-of drv);
drv-name = drv:
discard (substring 33 (stringLength (builtins.baseNameOf drv)) (builtins.baseNameOf drv));
replace-strings = drv: rewritten-drvs: runCommand (drv-name drv) { nixStore = "${nix}/bin/nix-store"; } ''
$nixStore --dump ${drv} | sed 's|${baseNameOf drv}|'$(basename $out)'|g' | sed -e ${
concatStringsSep " -e " (mapAttrsToList (name: value:
"'s|${baseNameOf name}|${baseNameOf value}|g'"
) rewritten-drvs)
} | $nixStore --restore $out
'';
fn = { drv, rewritten-drvs }: rewritten-drvs // (
if depends-on-old drv
then listToAttrs [ {
name = discard (toString drv);
value = replace-strings drv (rewritten-drvs // (fold (drv: acc:
(fn { inherit drv rewritten-drvs; }) // acc
) {} (references-of drv)));
} ]
else {}
);
in assert (stringLength old-dependency.name == stringLength new-dependency.name); getAttr (discard drv.outPath) (fn {
inherit drv;
rewritten-drvs = listToAttrs [ {name = discard old-dependency.outPath; value = new-dependency;} ];
})