anchor.diff:      '';
   
     /*
  -  * Create a forest of symlinks to the files in `paths'.
  -  *
  -  * Examples:
  -  * # adds symlinks of hello to current build.
  -  * { symlinkJoin, hello }:
  -  * symlinkJoin { name = "myhello"; paths = [ hello ]; }
  -  *
  -  * # adds symlinks of hello to current build and prints "links added"
  -  * { symlinkJoin, hello }:
  -  * symlinkJoin { name = "myhello"; paths = [ hello ]; postBuild = "echo links added"; }
  -  */
  +   * Create a forest of symlinks to the files in `paths'.
  +   *
  +   * This creates a single derivation that replicates the directory structure
  +   * of all the input paths.
  +   *
  +   * Examples:
  +   * # adds symlinks of hello to current build.
  +   * symlinkJoin { name = "myhello"; paths = [ pkgs.hello ]; }
  +   *
  +   * # adds symlinks of hello and stack to current build and prints "links added"
  +   * symlinkJoin { name = "myexample"; paths = [ pkgs.hello pkgs.stack ]; postBuild = "echo links added"; }
  +   *
  +   * This creates a derivation with a directory structure like the following:
  +   *
  +   * /nix/store/sglsr5g079a5235hy29da3mq3hv8sjmm-myexample
  +   * |-- bin
  +   * |   |-- hello -> /nix/store/qy93dp4a3rqyn2mz63fbxjg228hffwyw-hello-2.10/bin/hello
  +   * |   `-- stack -> /nix/store/6lzdpxshx78281vy056lbk553ijsdr44-stack-2.1.3.1/bin/stack
  +   * `-- share
  +   *     |-- bash-completion
  +   *     |   `-- completions
  +   *     |       `-- stack -> /nix/store/6lzdpxshx78281vy056lbk553ijsdr44-stack-2.1.3.1/share/bash-completion/completions/stack
  +   *     |-- fish
  +   *     |   `-- vendor_completions.d
  +   *     |       `-- stack.fish -> /nix/store/6lzdpxshx78281vy056lbk553ijsdr44-stack-2.1.3.1/share/fish/vendor_completions.d/stack.fish
  +   * ...
  +   *
  +   * symlinkJoin and linkFarm are similar functions, but they output
  +   * derivations with different structure.
  +   *
  +   * symlinkJoin is used to create a derivation with a familiar directory
  +   * structure (top-level bin/, share/, etc), but with all actual files being symlinks to
  +   * the files in the input derivations.
  +   *
  +   * symlinkJoin is used many places in nixpkgs to create a single derivation
  +   * that appears to contain binaries, libraries, documentation, etc from
  +   * multiple input derivations.
  +   *
  +   * linkFarm is instead used to create a simple derivation with symlinks to
  +   * other derivations.  A derivation created with linkFarm is often used in CI
  +   * as a easy way to build multiple derivations at once.
  +   */
     symlinkJoin =
       args_@{ name
            , paths
  
positive.code:       done < graph
      '';
  
  
    /*
     * Quickly create a set of symlinks to derivations.
     * entries is a list of attribute sets like
     * { name = "name" ; path = "/nix/store/..."; }
     *
     * Example:
     *
     * # Symlinks hello path in store to current $out/hello
     * linkFarm "hello" [ { name = "hello"; path = pkgs.hello; } ];
     *
     */
    linkFarm = name: entries: runCommand name { preferLocalBuild = true; allowSubstitutes = false; }
      ''mkdir -p $out
        cd $out
        ${lib.concatMapStrings (x: ''
            mkdir -p "$(dirname ${lib.escapeShellArg x.name})"
            ln -s ${lib.escapeShellArg x.path} ${lib.escapeShellArg x.name}
        '') entries}
      '';
  
    /*
     * Easily create a linkFarm from a set of derivations.
     *
     * This calls linkFarm with a list of entries created from the list of input
     * derivations.  It turns each input derivation into an attribute set
     * like { name = drv.name ; path = drv }, and passes this to linkFarm.
     *
     * Example:
     *
     * # Symlinks the hello, gcc, and ghc derivations in $out
     * linkFarmFromDrvs "example" [ pkgs.hello pkgs.gcc pkgs.ghc ]
     */
    linkFarmFromDrvs = name: drvs:
      let mkEntryFromDrv = drv: { name = drv.name; path = drv; };
      in linkFarm name (map mkEntryFromDrv drvs);
  
    /* Print an error message if the file with the specified name and
     * hash doesn't exist in the Nix store. This function should only
  
negative.code:         ${postBuild}
        '';
  
    /*
     * Quickly create a set of symlinks to derivations.
     *
     * This creates a simple derivation with symlinks to all inputs.
     *
     * entries is a list of attribute sets like
     * { name = "name" ; path = "/nix/store/..."; }
     *
     * Example:
     *
     * # Symlinks hello and stack paths in store to current $out/hello-test and
     * # $out/foobar.
     * linkFarm "myexample" [ { name = "hello-test"; path = pkgs.hello; } { name = "foobar"; path = pkgs.stack; } ]
     *
     * This creates a derivation with a directory structure like the following:
     *
     * /nix/store/qc5728m4sa344mbks99r3q05mymwm4rw-myexample
     * |-- foobar -> /nix/store/6lzdpxshx78281vy056lbk553ijsdr44-stack-2.1.3.1
     * `-- hello-test -> /nix/store/qy93dp4a3rqyn2mz63fbxjg228hffwyw-hello-2.10
     *
     * See the note on symlinkJoin for the difference between linkFarm and symlinkJoin.
     */
    linkFarm = name: entries: runCommand name { preferLocalBuild = true; allowSubstitutes = false; }
      ''mkdir -p $out
        cd $out
        ${lib.concatMapStrings (x: ''
            mkdir -p "$(dirname ${lib.escapeShellArg x.name})"
            ln -s ${lib.escapeShellArg x.path} ${lib.escapeShellArg x.name}
        '') entries}
      '';
  
    /*
     * Easily create a linkFarm from a set of derivations.
     *
     * This calls linkFarm with a list of entries created from the list of input
     * derivations.  It turns each input derivation into an attribute set
     * like { name = drv.name ; path = drv }, and passes this to linkFarm.
     *
     * Example:
     *
     * # Symlinks the hello, gcc, and ghc derivations in $out
     * linkFarmFromDrvs "myexample" [ pkgs.hello pkgs.gcc pkgs.ghc ]
     *
     * This creates a derivation with a directory structure like the following:
     *
     * /nix/store/m3s6wkjy9c3wy830201bqsb91nk2yj8c-myexample
     * |-- gcc-wrapper-9.2.0 -> /nix/store/fqhjxf9ii4w4gqcsx59fyw2vvj91486a-gcc-wrapper-9.2.0
     * |-- ghc-8.6.5 -> /nix/store/gnf3s07bglhbbk4y6m76sbh42siym0s6-ghc-8.6.5
     * `-- hello-2.10 -> /nix/store/k0ll91c4npk4lg8lqhx00glg2m735g74-hello-2.10
     */
    linkFarmFromDrvs = name: drvs:
      let mkEntryFromDrv = drv: { name = drv.name; path = drv; };
      in linkFarm name (map mkEntryFromDrv drvs);
  
  
    /*
     * Make a package that just contains a setup hook with the given contents.
  