Use image.includeStorePaths = false, no more "arion base image"

The arion base image was a poor substitute for the customization
layer that only worked for some images.

By modifying dockerTools to export only the customization layer,
we can support arbitrary root contents.

src/nix/modules.nix

@@ -3,6 +3,5 @@
     ./modules/composition/host-environment.nix
     ./modules/composition/images.nix
     ./modules/composition/service-info.nix
-    ./modules/composition/arion-base-image.nix
     ./modules/composition/composition.nix
 ]

src/nix/modules/composition/arion-base-image.nix

@@ -1,40 +0,0 @@
-
-
-# This module is subject to change.
-# In particular, arion-base should use a generic non-service image building system
-
-{ config, lib, pkgs, ... }: 
-
-let
-  name = "arion-base";
-
-  imageExe = pkgs.dockerTools.streamLayeredImage {
-    inherit name;
-    contents = pkgs.runCommand "minimal-contents" {} ''
-        mkdir -p $out/bin $out/usr/bin
-        ln -s /run/system/bin/sh $out/bin/sh
-        ln -s /run/system/usr/bin/env $out/usr/bin/env
-      '';
-    config = {};
-  };
-  inherit (imageExe) imageTag;
-
-in
-
-{
-
-  options = {
-    arionBaseImage = lib.mkOption {
-      type = lib.types.str;
-      description = "Image to use when using useHostStore. Don't use this option yourself. It's going away.";
-      internal = true;
-    };
-  };
-
-  config = {
-    arionBaseImage = "${name}:${imageTag}";
-    build.imagesToLoad = lib.mkIf (lib.any (s: s.service.useHostStore) (lib.attrValues config.services)) [
-      { imageExe = imageExe; imageName = name; inherit imageTag; }
-    ];  
-  };
-}

src/nix/modules/service/host-store.nix

@@ -29,12 +29,10 @@ in
     };
   };
   config = mkIf config.service.useHostStore {
-    image.nixBuild = false; # no need to build and load
-    service.image = config.composition.arionBaseImage;
+    image.includeStorePaths = false;
     service.environment.NIX_REMOTE = lib.optionalString config.service.useHostNixDaemon "daemon";
     service.volumes = [
       "${config.host.nixStorePrefix}/nix/store:/nix/store${lib.optionalString config.service.hostStoreAsReadOnly ":ro"}"
-      "${config.host.nixStorePrefix}${pkgs.buildEnv { name = "container-system-env"; paths = [ pkgs.bashInteractive pkgs.coreutils ]; }}:/run/system${lib.optionalString config.service.hostStoreAsReadOnly ":ro"}"
       ] ++ lib.optional config.service.useHostNixDaemon "/nix/var/nix/daemon-socket:/nix/var/nix/daemon-socket";
     service.command = lib.mkDefault (map escape (config.image.rawConfig.Cmd or []));
   };

src/nix/modules/service/image.nix

@@ -1,6 +1,15 @@
 { pkgs, lib, config, options, ... }:
 let
-  inherit (lib) types mkOption;
+  inherit (lib)
+    functionArgs
+    mkOption
+    optionalAttrs
+    types
+    warn
+    ;
+  inherit (pkgs)
+    dockerTools
+    ;
   inherit (types) attrsOf listOf nullOr package str unspecified bool;
 
   # TODO: dummy-config is a useless layer. Nix 2.3 will let us inspect
@@ -9,15 +18,37 @@ let
     (pkgs.writeText "dummy-config.json" (builtins.toJSON config.image.rawConfig))
   ];
 
+  includeStorePathsWarningAndDefault = lib.warn ''
+    You're using a version of Nixpkgs that doesn't support the includeStorePaths
+    parameter in dockerTools.streamLayeredImage. Without this, Arion's
+    useHostStore does not achieve the intended speedup.
+  '' {};
+
   buildOrStreamLayeredImage = args:
-    if pkgs.dockerTools?streamLayeredImage
-    then pkgs.dockerTools.streamLayeredImage args // { isExe = true; }
-    else pkgs.dockerTools.buildLayeredImage args;
+    let
+      args_base = builtins.intersectAttrs
+        {
+          name = null; tag = null; contents = null; config = null;
+          created = null; extraCommands = null; maxLayers = null;
+        }
+        args;
+      acceptedArgs = functionArgs dockerTools.streamLayeredImage;
+      args_no_store = lib.optionalAttrs (!(args.includeStorePaths or true)) (
+        if acceptedArgs ? includeStorePaths
+        then { inherit (args) includeStorePaths; }
+        else includeStorePathsWarningAndDefault
+      );
+      args_streamLayered = args_base // args_no_store;
+    in
+      if dockerTools?streamLayeredImage
+      then dockerTools.streamLayeredImage args_streamLayered // { isExe = true; }
+      else dockerTools.buildLayeredImage args_base;
 
   builtImage = buildOrStreamLayeredImage {
     inherit (config.image)
       name
       contents
+      includeStorePaths
       ;
     config = config.image.rawConfig;
     maxLayers = 100;
@@ -89,6 +120,15 @@ in
          Top level paths in the container.
       '';
     };
+    image.includeStorePaths = mkOption {
+      type = bool;
+      default = true;
+      internal = true;
+      description = ''
+        Include all referenced store paths. You generally want this in your
+        image, unless you load store paths via some other means, like useHostStore = true;
+      '';
+    };
     image.rawConfig = mkOption {
       type = attrsOf unspecified;
       default = {};