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{ 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: safeFirefox = replaceDependency {
# drv = firefox;
# oldDependency = glibc;
# newDependency = 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, oldDependency, newDependency, verbose ? true }:
with lib;
let
warn = if verbose then builtins.trace else (x: y: y);
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 }) > $out
'').outPath;
discard = builtins.unsafeDiscardStringContext;
oldStorepath = builtins.storePath (discard (toString oldDependency));
referencesOf = drv: references.${discard (toString drv)};
dependsOnOldMemo = listToAttrs (map
(drv: { name = discard (toString drv);
value = elem oldStorepath (referencesOf drv) ||
any dependsOnOld (referencesOf drv);
}) (builtins.attrNames references));
dependsOnOld = drv: dependsOnOldMemo.${discard (toString drv)};
drvName = drv:
discard (substring 33 (stringLength (builtins.baseNameOf drv)) (builtins.baseNameOf drv));
rewriteHashes = drv: hashes: runCommand (drvName drv) { nixStore = "${nix.out}/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'"
) hashes)
} | $nixStore --restore $out
'';
rewrittenDeps = listToAttrs [ {name = discard (toString oldDependency); value = newDependency;} ];
rewriteMemo = listToAttrs (map
(drv: { name = discard (toString drv);
value = rewriteHashes (builtins.storePath drv)
(filterAttrs (n: v: builtins.elem (builtins.storePath (discard (toString n))) (referencesOf drv)) rewriteMemo);
})
(filter dependsOnOld (builtins.attrNames references))) // rewrittenDeps;
drvHash = discard (toString drv);
in assert (stringLength (drvName (toString oldDependency)) == stringLength (drvName (toString newDependency)));
rewriteMemo.${drvHash} or (warn "replace-dependency.nix: Derivation ${drvHash} does not depend on ${discard (toString oldDependency)}" drv)