chore(build-image): Simplify wrapper build & remove layer grouping

Simplifies the wrapper script used to invoke Nix builds from Nixery to
just contain the essentials, since the layer grouping logic is moving
into the server itself.

1 files changed, 15 insertions, 81 deletions

diff --git a/tools/nixery/build-image/default.nix b/tools/nixery/build-image/default.nix
index 3bb5d62fb0d5..a61ac06bdd92 100644
--- a/tools/nixery/build-image/default.nix
+++ b/tools/nixery/build-image/default.nix
@@ -12,84 +12,18 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-# This file builds the tool used to calculate layer distribution and
-# moves the files needed to call the Nix builds at runtime in the
-# correct locations.
-
-{ pkgs ? null, self ? ./.
-
-  # Because of the insanity occuring below, this function must mirror
-  # all arguments of build-image.nix.
-, srcType ? "nixpkgs"
-, srcArgs ? "nixos-19.03"
-, tag ? null, name ? null, packages ? null, maxLayers ? null, popularityUrl ? null
-}@args:
-
-let pkgs = import ./load-pkgs.nix { inherit srcType srcArgs; };
-in with pkgs; rec {
-
-  groupLayers = buildGoPackage {
-    name = "group-layers";
-    goDeps = ./go-deps.nix;
-    goPackagePath = "github.com/google/nixery/group-layers";
-
-    # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #
-    #                    WARNING: HERE BE DRAGONS!                    #
-    #                                                                 #
-    # The hack below is used to break evaluation purity. The issue is #
-    # that Nixery's build instructions (the default.nix in the folder #
-    # above this one) must build a program that can invoke Nix at     #
-    # runtime, with a derivation that needs a program tracked in this #
-    # source tree (`group-layers`).                                   #
-    #                                                                 #
-    # Simply installing that program in the $PATH of Nixery does not  #
-    # work, because the runtime Nix builds use their own isolated     #
-    # environment.                                                    #
-    #                                                                 #
-    # I first attempted to naively copy the sources into the Nix      #
-    # store, so that Nixery could build `group-layers` when it starts #
-    # up - however those sources are not available to a nested Nix    #
-    # build because they're not part of the context of the nested     #
-    # invocation.                                                     #
-    #                                                                 #
-    # Nix has several primitives under `builtins.` that can break     #
-    # evaluation purity, these (namely readDir and readFile) are used #
-    # below to break out of the isolated environment and reconstruct  #
-    # the source tree for `group-layers`.                             #
-    #                                                                 #
-    # There might be a better way to do this, but I don't know what   #
-    # it is.                                                          #
-    # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # #
-    src = runCommand "group-layers-srcs" { } ''
-      mkdir -p $out
-      ${with builtins;
-      let
-        files =
-          (attrNames (lib.filterAttrs (_: t: t != "symlink") (readDir self)));
-        commands =
-          map (f: "cp ${toFile f (readFile "${self}/${f}")} $out/${f}") files;
-      in lib.concatStringsSep "\n" commands}
-    '';
-
-    meta = {
-      description =
-        "Tool to group a set of packages into container image layers";
-      license = lib.licenses.asl20;
-      maintainers = [ lib.maintainers.tazjin ];
-    };
-  };
-
-  buildImage = import ./build-image.nix
-    ({ inherit pkgs groupLayers; } // (lib.filterAttrs (_: v: v != null) args));
-
-  # Wrapper script which is called by the Nixery server to trigger an
-  # actual image build. This exists to avoid having to specify the
-  # location of build-image.nix at runtime.
-  wrapper = writeShellScriptBin "nixery-build-image" ''
-    exec ${nix}/bin/nix-build \
-      --show-trace \
-      --no-out-link "$@" \
-      --argstr self "${./.}" \
-      -A buildImage ${./.}
-  '';
-}
+# This file builds a wrapper script called by Nixery to ask for the
+# content information for a given image.
+#
+# The purpose of using a wrapper script is to ensure that the paths to
+# all required Nix files are set correctly at runtime.
+
+{ pkgs ? import <nixpkgs> {} }:
+
+pkgs.writeShellScriptBin "nixery-build-image" ''
+  exec ${pkgs.nix}/bin/nix-build \
+    --show-trace \
+    --no-out-link "$@" \
+    --argstr loadPkgs ${./load-pkgs.nix} \
+    ${./build-image.nix}
+''