replace-direct-dependencies.nix

{
  lib,
  runCommandLocal,
  nix,
}:

# Replace some direct dependencies of drv, not recursing into the dependency tree.
# You likely want to use replaceDependencies instead, unless you plan to implement your own recursion mechanism.
{
  drv,
  replacements ? [ ],
}:
let
  inherit (lib)
    isStorePath
    substring
    stringLength
    optionalString
    escapeShellArgs
    concatMap
    ;
in
if replacements == [ ] then
  drv
else
  let
    drvName =
      if isStorePath drv then
        # Reconstruct the name from the actual store path if available.
        substring 33 (stringLength (baseNameOf drv)) (baseNameOf drv)
      else if drv ? drvAttrs.name then
        # Try to get the name from the derivation arguments otherwise (for floating or deferred derivations).
        drv.drvAttrs.name
        + (
          let
            outputName = drv.outputName or "out";
          in
          optionalString (outputName != "out") "-${outputName}"
        )
      else
        throw "cannot reconstruct the derivation name from ${drv}";
  in
  runCommandLocal drvName { nativeBuildInputs = [ nix.out ]; } ''
    createRewriteScript() {
        while [ $# -ne 0 ]; do
            oldBasename="$(basename "$1")"
            newBasename="$(basename "$2")"
            shift 2
            if [ ''${#oldBasename} -ne ''${#newBasename} ]; then
                echo "cannot rewrite $oldBasename to $newBasename: length does not match" >&2
                exit 1
            fi
            echo "s|$oldBasename|$newBasename|g" >> rewrite.sed
        done
    }
    createRewriteScript ${
      escapeShellArgs (
        [
          drv
          (placeholder "out")
        ]
        ++ concatMap (
          { oldDependency, newDependency }:
          [
            oldDependency
            newDependency
          ]
        ) replacements
      )
    }
    nix-store --dump ${drv} | sed -f rewrite.sed | nix-store --restore $out
  ''