core/pkgs/build-support/replace-dependency.nix

{
  runCommandLocal,
  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,
}:

let
  inherit (lib)
    any
    attrNames
    concatStringsSep
    elem
    filter
    filterAttrs
    listToAttrs
    mapAttrsToList
    stringLength
    substring
    ;

  warn = if verbose then builtins.trace else (x: y: y);
  references =
    import
      (runCommandLocal "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);
    }) (attrNames references)
  );

  dependsOnOld = drv: dependsOnOldMemo.${discard (toString drv)};

  drvName =
    drv: discard (substring 33 (stringLength (builtins.baseNameOf drv)) (builtins.baseNameOf drv));

  rewriteHashes =
    drv: hashes:
    runCommandLocal (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: elem (builtins.storePath (discard (toString n))) (referencesOf drv)) rewriteMemo
        );
      }) (filter dependsOnOld (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)