serialised.nix

let                                                                                                                                                                                                                                                                                                                          
  pkgs = import <nixpkgs> { };                                                                                                                                                                                                                                                                                               
  inherit (pkgs.stdenv) mkDerivation;                                                                                                                                                                                                                                                                                        
                                                                                                                                                                                                                                                                                                                             
  collectSymlinks = { name, inputs, include ? null }: mkDerivation {                                                                                                                                                                                                                                                         
    name = "collect-${name}";                                                                                                                                                                                                                                                                                                
    buildInputs = inputs;                                                                                                                                                                                                                                                                                                    
    buildCommand =                                                                                                                                                                                                                                                                                                           
      let                                                                                                                                                                                                                                                                                                                    
        copyInput = input:                                                                                                                                                                                                                                                                                                   
          let outs = builtins.attrNames (builtins.readDir input.outPath);                                                                                                                                                                                                                                                    
          in "ln -s ${input}/${builtins.elemAt outs 0} $out/${input.name}";                                                                                                                                                                                                                                                  
      in ''                                                                                                                                                                                                                                                                                                                  
      mkdir $out                                                                                                                                                                                                                                                                                                             
      ${pkgs.lib.concatMapStringsSep "\n" copyInput inputs}                                                                                                                                                                                                                                                                      '';                                                                                                                                                                                                                                                                                                                      
  };                                                                                                                                                                                                                                                                                                                         
                                                                                                                                                                                                                                                                                                                             
  testIt =                                                                                                                                                                                                                                                                                                                   
    let                                                                                                                                                                                                                                                                                                                      
      testDrv = i: mkDerivation {                                                                                                                                                                                                                                                                                            
        name = "drv-${builtins.toString i}";                                                                                                                                                                                                                                                                                 
        buildCommand = ''                                                                                                                                                                                                                                                                                                    
          echo Building $i                                                                                                                                                                                                                                                                                                   
          sleep 5                                                                                                                                                                                                                                                                                                            
          mkdir $out                                                                                                                                                                                                                                                                                                         
          cp ${./test.nix} $out/                                                                                                                                                                                                                                                                                             
        '';                                                                                                                                                                                                                                                                                                                  
      };                                                                                                                                                                                                                                                                                                                     
    in collectSymlinks { name = "testit"; inputs = pkgs.lib.genList testDrv 5; };                                                                                                                                                                                                                                            
in testIt