From 4883af6edbdf222c66edb545d312f4e40030a2be Mon Sep 17 00:00:00 2001
From: Austin Horstman <khaneliman12@gmail.com>
Date: Mon, 20 Apr 2026 08:22:51 -0500
Subject: [PATCH] syncthing: avoid init for default gui address

The gui address option always has a default value, so #8644 ended up
making syncthing-init run for every enabled Syncthing setup.

Treat the default gui address as unset for updater purposes so the init
unit is only generated when Home Manager is actually managing Syncthing
configuration. Add regression tests for the default and explicit
guiAddress cases.
---
 modules/services/syncthing.nix                   | 10 +++++++---
 .../modules/services/syncthing/extra-options.nix |  3 +++
 .../modules/services/syncthing/linux/default.nix |  1 +
 .../syncthing/linux/gui-address-init.nix         | 16 ++++++++++++++++
 4 files changed, 27 insertions(+), 3 deletions(-)
 create mode 100644 tests/modules/services/syncthing/linux/gui-address-init.nix

diff --git a/modules/services/syncthing.nix b/modules/services/syncthing.nix
index 839ec9b16..125b05f3c 100644
--- a/modules/services/syncthing.nix
+++ b/modules/services/syncthing.nix
@@ -25,6 +25,10 @@ let
     else
       "\${XDG_STATE_HOME:-$HOME/.local/state}/syncthing";
 
+  defaultGuiAddress = "127.0.0.1:8384";
+
+  hasCustomGuiAddress = cfg.guiAddress != defaultGuiAddress;
+
   # Syncthing supports serving the GUI over Unix sockets. If that happens, the
   # API is served over the Unix socket as well.  This function returns the correct
   # curl arguments for the address portion of the curl command for both network
@@ -288,7 +292,7 @@ let
         ''))
         (lib.concatStringsSep "\n")
       ])
-    + lib.optionalString (cfg.guiAddress != null) ''
+    + lib.optionalString hasCustomGuiAddress ''
       curl -X PATCH -d '{"address": "'${cfg.guiAddress}'"}' ${curlAddressArgs "/rest/config/gui"}
     ''
     + ''
@@ -300,7 +304,7 @@ let
     ''
   );
 
-  doUpdateConfig = cleanedConfig != { } || cfg.guiCredentials != null || cfg.guiAddress != null;
+  doUpdateConfig = cleanedConfig != { } || cfg.guiCredentials != null || hasCustomGuiAddress;
 
   defaultSyncthingArgs = [
     "${syncthing}"
@@ -771,7 +775,7 @@ in
 
       guiAddress = mkOption {
         type = types.str;
-        default = "127.0.0.1:8384";
+        default = defaultGuiAddress;
         description = ''
           The address to serve the web interface at.
         '';
diff --git a/tests/modules/services/syncthing/extra-options.nix b/tests/modules/services/syncthing/extra-options.nix
index 8f80b6aa4..e59b440ab 100644
--- a/tests/modules/services/syncthing/extra-options.nix
+++ b/tests/modules/services/syncthing/extra-options.nix
@@ -18,6 +18,8 @@ lib.mkMerge [
   (lib.mkIf pkgs.stdenv.isLinux {
     nmt.script = ''
       assertFileExists home-files/.config/systemd/user/syncthing.service
+      assertPathNotExists home-files/.config/systemd/user/syncthing-init.service
+      assertPathNotExists home-files/.config/systemd/user/default.target.wants/syncthing-init.service
       assertFileContains home-files/.config/systemd/user/syncthing.service \
       "ExecStart=@syncthing@/bin/syncthing serve --no-browser --no-restart --no-upgrade '--gui-address=127.0.0.1:8384' -foo '-bar \"baz\"'"
     '';
@@ -27,6 +29,7 @@ lib.mkMerge [
     nmt.script = ''
       serviceFile=LaunchAgents/org.nix-community.home.syncthing.plist
       assertFileExists "$serviceFile"
+      assertPathNotExists LaunchAgents/org.nix-community.home.syncthing-init.plist
       assertFileContent "$serviceFile" ${./expected-agent.plist}
     '';
   })
diff --git a/tests/modules/services/syncthing/linux/default.nix b/tests/modules/services/syncthing/linux/default.nix
index da4505040..cd3c7ab59 100644
--- a/tests/modules/services/syncthing/linux/default.nix
+++ b/tests/modules/services/syncthing/linux/default.nix
@@ -1,3 +1,4 @@
 {
+  syncthing-gui-address-init = ./gui-address-init.nix;
   syncthing-tray = ./tray.nix;
 }
diff --git a/tests/modules/services/syncthing/linux/gui-address-init.nix b/tests/modules/services/syncthing/linux/gui-address-init.nix
new file mode 100644
index 000000000..24cbd9a2c
--- /dev/null
+++ b/tests/modules/services/syncthing/linux/gui-address-init.nix
@@ -0,0 +1,16 @@
+{
+  services.syncthing = {
+    enable = true;
+    guiAddress = "127.0.0.1:8385";
+  };
+
+  nmt.script = ''
+    serviceFile=home-files/.config/systemd/user/syncthing-init.service
+    assertFileExists "$serviceFile"
+    assertFileExists home-files/.config/systemd/user/default.target.wants/syncthing-init.service
+    assertFileContains "$serviceFile" "ExecStart="
+
+    updateScript=$(grep -o '/nix/store/[^ ]*-merge-syncthing-config' "$TESTED/$serviceFile")
+    assertFileContains "$updateScript" "127.0.0.1:8385/rest/config/gui"
+  '';
+}