dockerTools.buildImageWithNixDb: simplifications and switch to closureInfo

Since Nix 2 is now the stable Nix version, we can use closureInfo
which simplifies the Nix database initialisation (size and hash are
included in the "dump").

pkgs/build-support/docker/default.nix

@@ -11,7 +11,6 @@
   pkgs,
   pigz,
   nix,
-  perl,
   runCommand,
   rsync,
   shadow,
@@ -23,6 +22,7 @@
   referencesByPopularity,
   writeScript,
   writeText,
+  closureInfo
 }:
 
 # WARNING: this API is unstable and may be subject to backwards-incompatible changes in the future.
@@ -261,19 +261,6 @@ rec {
       ${text}
     '';
 
-  nixRegistration = contents: runCommand "nix-registration" {
-    buildInputs = [ nix perl ];
-    # For obtaining the closure of `contents'.
-    exportReferencesGraph =
-      let contentsList = if builtins.isList contents then contents else [ contents ];
-      in map (x: [("closure-" + baseNameOf x) x]) contentsList;
-    }
-    ''
-      mkdir $out
-      printRegistration=1 perl ${pkgs.pathsFromGraph} closure-* > $out/db.dump
-      perl ${pkgs.pathsFromGraph} closure-* > $out/storePaths
-    '';
-
   # Create $maxLayers worth of Docker Layers, one layer per store path
   # unless there are more paths than $maxLayers. In that case, create
   # $maxLayers-1 for the most popular layers, and smush the remainaing
@@ -795,29 +782,19 @@ rec {
   # the container.
   # Be careful since this doesn't work well with multilayer.
   buildImageWithNixDb = args@{ contents ? null, extraCommands ? "", ... }:
-    buildImage (args // {
+    let contentsList = if builtins.isList contents then contents else [ contents ];
+    in buildImage (args // {
       extraCommands = ''
         echo "Generating the nix database..."
         echo "Warning: only the database of the deepest Nix layer is loaded."
         echo "         If you want to use nix commands in the container, it would"
         echo "         be better to only have one layer that contains a nix store."
-        # This requires Nix 1.12 or higher
-        export NIX_REMOTE=local?root=$PWD
-        ${nix}/bin/nix-store --load-db < ${nixRegistration contents}/db.dump
 
-        # We fill the store in order to run the 'verify' command that
+        export NIX_REMOTE=local?root=$PWD
-        # generates hash and size of output paths.
+        ${nix}/bin/nix-store --load-db < ${closureInfo {rootPaths = contentsList;}}/registration
-        # Note when Nix 1.12 is be the stable one, the database dump
-        # generated by the exportReferencesGraph function will
-        # contains sha and size. See
-        # https://github.com/NixOS/nix/commit/c2b0d8749f7e77afc1c4b3e8dd36b7ee9720af4a
-        storePaths=$(cat ${nixRegistration contents}/storePaths)
-        echo "Copying everything to /nix/store (will take a while)..."
-        cp -prd $storePaths nix/store/
-        ${nix}/bin/nix-store --verify --check-contents
 
         mkdir -p nix/var/nix/gcroots/docker/
-        for i in ${lib.concatStringsSep " " contents}; do
+        for i in ${lib.concatStringsSep " " contentsList}; do
           ln -s $i nix/var/nix/gcroots/docker/$(basename $i)
         done;
       '' + extraCommands;