Can somebody help, i've created a monster... now want it to be alive.
How to test:
nix-instantiate --eval --strict -E 'toString (import ./build_inputs_1.nix { pkg = (import <nixpkgs> {}).hello; })'
Create file build_inputs_1.nix with:

{ pkg, lib ? import <nixpkgs/lib> }:
let
  drv_direct_dependencies =
    drv_path:
    let
      drv_file = builtins.readFile drv_path;
      storeDirRe = lib.replaceStrings [ "." ] [ "\\." ] builtins.storeDir;
      storeBaseRe = "[0-9a-df-np-sv-z]{32}-[+_?=a-zA-Z0-9-][+_?=.a-zA-Z0-9-]*";
      re = "(${storeDirRe}/${storeBaseRe}\\.drv)";
      inputs = lib.concatLists (lib.filter lib.isList (builtins.split re drv_file));
    in
    inputs;

  drv_all_dependencies = { drv_path, visited }:
    let
      direct_dependencies = drv_direct_dependencies drv_path;
      minimal_path = { paths = [ drv_path ]; visited = visited ++ [ drv_path ]; };
      just_visited = { paths = [ ]; visited = visited ++ [ drv_path ];};
      concat_outs = (out1: out2: { paths = out1.paths ++ out2.paths; visited = out1.visited ++ out2.visited; });
      visit_all_childs = (out: dependency:
      if (builtins.elem dependency out.visited) then out
      else concat_outs out (drv_all_dependencies { drv_path = dependency; visited = out.visited; }));
      result =
        if (builtins.length direct_dependencies) == 0 then minimal_path
        else concat_outs (builtins.foldl' visit_all_childs just_visited direct_dependencies) minimal_path;
    in
    result;
in
(drv_all_dependencies { drv_path = pkg.drvPath; visited = [ ]; }).paths

Problem:
GC Warning: Repeated allocation of very large block (appr. size 2525917184):

but it works on small example (only 4 derivations in chain).

What i try to achieve: given drv_path function must reaturn a list, containing all derivations which need to be build in order to build derivation from drv_path. list should be ordered, so first on list is most needed derivation, last on list - derivation from given path.

In reply to @qyliss:fairydust.space
hmm, this channel isn't going to be the same without puck