nix/drvSeqL/default.nix


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{ depot, lib, pkgs, ... }:

let

  inherit (depot.nix.yants)
    defun
    list
    drv
    ;

  /* Realize drvDeps, then return drvOut if that succeds.
   * This can be used to make drvOut depend on the
   * build success of all drvDeps without making each drvDep
   * a dependency of drvOut.
   * => drvOut is not rebuilt if drvDep changes
   */
  drvSeqL = defun [ (list drv) drv drv ]
    (drvDeps: drvOut:
      let
        drvOutOutputs = drvOut.outputs or ["out"];
      in
        pkgs.runCommandLocal drvOut.name {
          # we inherit all attributes in order to replicate
          # the original derivation as much as possible
          outputs = drvOutOutputs;
          passthru = drvOut.drvAttrs;
          # depend on drvDeps (by putting it in builder context)
          inherit drvDeps;
        }
        # the outputs of the original derivation are replicated
        # by creating a symlink to the old output path
        (lib.concatMapStrings (output: ''
          target=${lib.escapeShellArg drvOut.${output}}
          # if the target is already a symlink, follow it until it’s not;
          # this is done to prevent too many dereferences
          target=$(readlink -e "$target")
          # link to the output
          ln -s "$target" "${"$"}${output}"
        '') drvOutOutputs));

in {
  __functor = _: drvSeqL;
}