From aa91e7f0b5b21de94a0d8bce43e0fe2a3c0e8a4d Mon Sep 17 00:00:00 2001
From: ivan770 <ivan@ivan770.me>
Date: Sat, 25 May 2024 08:41:24 -0400
Subject: [PATCH] nixos/etc: support direct symlinks with etc overlay

(cherry picked from commit 1b288bca003d5c9edc851bbf268c43591cea3aac)
---
 .../system/etc/build-composefs-dump.py        | 35 +++++++++----------
 nixos/modules/system/etc/etc.nix              |  2 +-
 .../activation/etc-overlay-immutable.nix      |  4 +++
 3 files changed, 22 insertions(+), 19 deletions(-)

diff --git a/nixos/modules/system/etc/build-composefs-dump.py b/nixos/modules/system/etc/build-composefs-dump.py
index bba454dd888d6..fe739a621ec4d 100644
--- a/nixos/modules/system/etc/build-composefs-dump.py
+++ b/nixos/modules/system/etc/build-composefs-dump.py
@@ -175,7 +175,7 @@ def main() -> None:
                 paths[glob_target] = composefs_path
                 add_leading_directories(glob_target, attrs, paths)
         else:  # Without globbing
-            if mode == "symlink":
+            if mode == "symlink" or mode == "direct-symlink":
                 composefs_path = ComposefsPath(
                     attrs,
                     # A high approximation of the size of a symlink
@@ -184,24 +184,23 @@ def main() -> None:
                     mode="0777",
                     payload=source,
                 )
+            elif os.path.isdir(source):
+                composefs_path = ComposefsPath(
+                    attrs,
+                    size=4096,
+                    filetype=FileType.directory,
+                    mode=mode,
+                    payload=source,
+                )
             else:
-                if os.path.isdir(source):
-                    composefs_path = ComposefsPath(
-                        attrs,
-                        size=4096,
-                        filetype=FileType.directory,
-                        mode=mode,
-                        payload=source,
-                    )
-                else:
-                    composefs_path = ComposefsPath(
-                        attrs,
-                        size=os.stat(source).st_size,
-                        filetype=FileType.file,
-                        mode=mode,
-                        # payload needs to be relative path in this case
-                        payload=target.lstrip("/"),
-                    )
+                composefs_path = ComposefsPath(
+                    attrs,
+                    size=os.stat(source).st_size,
+                    filetype=FileType.file,
+                    mode=mode,
+                    # payload needs to be relative path in this case
+                    payload=target.lstrip("/"),
+                )
             paths[target] = composefs_path
             add_leading_directories(target, attrs, paths)
 
diff --git a/nixos/modules/system/etc/etc.nix b/nixos/modules/system/etc/etc.nix
index 9fded1e1c9742..80ca69e495e9d 100644
--- a/nixos/modules/system/etc/etc.nix
+++ b/nixos/modules/system/etc/etc.nix
@@ -62,7 +62,7 @@ let
     ]) etc'}
   '';
 
-  etcHardlinks = filter (f: f.mode != "symlink") etc';
+  etcHardlinks = filter (f: f.mode != "symlink" && f.mode != "direct-symlink") etc';
 
   build-composefs-dump = pkgs.runCommand "build-composefs-dump.py"
     {
diff --git a/nixos/tests/activation/etc-overlay-immutable.nix b/nixos/tests/activation/etc-overlay-immutable.nix
index f347f9cf8efe2..f0abf70d350ff 100644
--- a/nixos/tests/activation/etc-overlay-immutable.nix
+++ b/nixos/tests/activation/etc-overlay-immutable.nix
@@ -13,6 +13,7 @@
     users.mutableUsers = false;
     boot.initrd.systemd.enable = true;
     boot.kernelPackages = pkgs.linuxPackages_latest;
+    time.timeZone = "Utc";
 
     specialisation.new-generation.configuration = {
       environment.etc."newgen".text = "newgen";
@@ -23,6 +24,9 @@
     with subtest("/etc is mounted as an overlay"):
       machine.succeed("findmnt --kernel --type overlay /etc")
 
+    with subtest("direct symlinks point to the target without indirection"):
+      assert machine.succeed("readlink -n /etc/localtime") == "/etc/zoneinfo/Utc"
+
     with subtest("switching to the same generation"):
       machine.succeed("/run/current-system/bin/switch-to-configuration test")