Add image.enableRecommendedContents for /bin/sh and such

docs/modules/ROOT/partials/NixOSOptions.adoc

@@ -197,6 +197,25 @@ Default::
 ----
 
 
+No Example:: {blank}
+
+== services.<name>.image.enableRecommendedContents
+
+Add the `/bin/sh` and `/usr/bin/env` symlinks and some lightweight
+files.
+
+
+[discrete]
+=== details
+
+Type:: boolean
+Default::
++
+----
+false
+----
+
+
 No Example:: {blank}
 
 == services.<name>.image.name

examples/minimal/arion-compose.nix

@@ -4,6 +4,7 @@
   config.services = {
 
     webserver = {
+      image.enableRecommendedContents = true;
       service.useHostStore = true;
       service.command = [ "sh" "-c" ''
                   cd "$$WEB_ROOT"

src/nix/modules/service/all-modules.nix

@@ -5,6 +5,7 @@
   ./host-store.nix
   ./context.nix
   ./image.nix
+  ./image-recommended.nix
   ./nixos.nix
   ./nixos-init.nix
   ../lib/assert.nix

src/nix/modules/service/image-recommended.nix

@@ -0,0 +1,36 @@
+{ config, lib, pkgs, ... }:
+let
+  inherit (lib)
+    mkIf
+    mkOption
+    types
+    ;
+  inherit (types)
+    bool
+    ;
+
+  recommendedContents = { runCommand, bash, coreutils }:
+    runCommand "recommended-contents" {} ''
+      mkdir -p $out/bin $out/usr/bin $out/var/empty
+      ln -s ${bash}/bin/sh $out/bin/sh
+      ln -s ${coreutils}/bin/env $out/usr/bin/env
+    '';
+in
+{
+  options = {
+    image.enableRecommendedContents = mkOption {
+      type = bool;
+      default = false;
+      description = ''
+        Add the `/bin/sh` and `/usr/bin/env` symlinks and some lightweight
+        files.
+      '';
+    };
+  };
+
+  config = {
+    image.contents = mkIf config.image.enableRecommendedContents [
+      (pkgs.callPackage recommendedContents {})
+    ];
+  };
+}