From 3cf11923ebd3648ec8cd51414eb302827d9c4ce8 Mon Sep 17 00:00:00 2001
From: Daiderd Jordan <daiderd@gmail.com>
Date: Sat, 19 Dec 2020 11:37:54 +0100
Subject: [PATCH] use --dry-run check to re-apply system patches

---
 modules/system/patches.nix | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/modules/system/patches.nix b/modules/system/patches.nix
index 855d23f..0ef3e73 100644
--- a/modules/system/patches.nix
+++ b/modules/system/patches.nix
@@ -29,6 +29,10 @@ in
       description = ''
         Set of patches to apply to <filename>/</filename>.
 
+        <warning>
+        <para>This can modify everything so use with caution.</para>
+        </warning>
+
         Useful for safely changing system files.  Unlike the etc module this
         won't remove or modify files with unexpected content.
       '';
@@ -56,12 +60,12 @@ in
           fi
       done
 
-        ${concatMapStringsSep "\n" (f: ''
-          f="$(basename ${f})"
-          if ! diff "${cfg.build.patches}/patches/$f" "/run/current-system/patches/$f" &> /dev/null; then
-              patch --forward --backup -d / -p1 < '${f}' || true
-          fi
-        '') cfg.patches}
+      ${concatMapStringsSep "\n" (f: ''
+        f="$(basename ${f})"
+        if ! patch --reverse --dry-run -d / -p1 < '${f}' &> /dev/null; then
+            patch --forward --backup -d / -p1 < '${f}' || true
+        fi
+      '') cfg.patches}
     '';
 
   };