From cad65d269e97d4480793f35d0cd697f1f0eb1621 Mon Sep 17 00:00:00 2001
From: Samuel Dionne-Riel <samuel@dionne-riel.com>
Date: Thu, 2 Feb 2023 16:20:53 -0500
Subject: [PATCH] image-builder: Prevent bogus empty filesystems

---
 overlay/image-builder/filesystem-image/basic.nix | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/overlay/image-builder/filesystem-image/basic.nix b/overlay/image-builder/filesystem-image/basic.nix
index 42d0886b..07c257f0 100644
--- a/overlay/image-builder/filesystem-image/basic.nix
+++ b/overlay/image-builder/filesystem-image/basic.nix
@@ -238,6 +238,19 @@ in
         (
           cd "$files"
           ${config.populateCommands}
+
+          # This also activates dotglob automatically.
+          # Using this means hidden files will be added too.
+          GLOBIGNORE=".:.."
+
+          if (( $(find -maxdepth 1 | wc -l) == 1 )); then
+            (set -x; ls -l)
+
+            echo ""
+            echo "ERROR: populatePhase produced no files."
+            echo "       tip: using mkForce or mkDefault at different places may unexpected overwrite values."
+            exit 2
+          fi
         )
       '';