dockerTools: test that tar keeps nix binary symlinks intact

nixos/tests/docker-tools.nix

@@ -42,6 +42,20 @@ import ./make-test-python.nix ({ pkgs, ... }: {
             "docker rmi ${examples.nix.imageName}",
         )
 
+    with subtest("The nix binary symlinks are intact"):
+        docker.succeed(
+            "docker load --input='${examples.nix}'",
+            "docker run --rm ${examples.nix.imageName} ${pkgs.bash}/bin/bash -c 'test nix == $(readlink ${pkgs.nix}/bin/nix-daemon)'",
+            "docker rmi ${examples.nix.imageName}",
+        )
+
+    with subtest("The nix binary symlinks are intact when the image is layered"):
+        docker.succeed(
+            "docker load --input='${examples.nixLayered}'",
+            "docker run --rm ${examples.nixLayered.imageName} ${pkgs.bash}/bin/bash -c 'test nix == $(readlink ${pkgs.nix}/bin/nix-daemon)'",
+            "docker rmi ${examples.nixLayered.imageName}",
+        )
+
     with subtest("The pullImage tool works"):
         docker.succeed(
             "docker load --input='${examples.nixFromDockerHub}'",

pkgs/build-support/docker/examples.nix

@@ -121,6 +121,7 @@ rec {
       # the image env variable NIX_PAGER.
       pkgs.coreutils
       pkgs.nix
+      pkgs.bash
     ];
     config = {
       Env = [
@@ -313,4 +314,25 @@ rec {
       )
     ];
   };
+
+  nixLayered = pkgs.dockerTools.buildLayeredImageWithNixDb {
+    name = "nix-layered";
+    tag = "latest";
+    contents = [
+      # nix-store uses cat program to display results as specified by
+      # the image env variable NIX_PAGER.
+      pkgs.coreutils
+      pkgs.nix
+      pkgs.bash
+    ];
+    config = {
+      Env = [
+        "NIX_PAGER=cat"
+        # A user is required by nix
+        # https://github.com/NixOS/nix/blob/9348f9291e5d9e4ba3c4347ea1b235640f54fd79/src/libutil/util.cc#L478
+        "USER=nobody"
+      ];
+    };
+  };
+
 }