modular-services: add config files to X-Reload-Triggers

Assisted-by: Claude:claude-sonnet-4-7

Signed-off-by: cinereal <cinereal@riseup.net>

docs/manual/usage/modular-services.md

@@ -58,6 +58,15 @@ can refer to its files at a stable location:
 }
 ```
 
+The store paths of all enabled `configData` entries are automatically
+added to the primary unit's `X-Reload-Triggers`, so `home-manager switch`
+restarts the service whenever any of its configuration files change. To
+reload instead of restart, override `X-SwitchMethod`:
+
+```nix
+home.services.demo.systemd.services."".unitConfig.X-SwitchMethod = "reload";
+```
+
 ## Scope notes {#sec-usage-modular-services-scope}
 
 Home Manager mirrors the surface of nixpkgs' portable systemd module:

modules/services-modular/default.nix

@@ -106,10 +106,45 @@ let
         ];
       }).config;
 
+  # Collect the `source` store paths of a service's enabled `configData`
+  # entries. When `text` is set, the upstream `config-data-item.nix` module
+  # automatically derives `source` via `pkgs.writeText`, so `source` is
+  # always non-null for enabled entries.
+  configDataSources =
+    service:
+    lib.mapAttrsToList (_: cfg: cfg.source) (
+      lib.filterAttrs (_: cfg: cfg.enable) (service.configData or { })
+    );
+
   makeUnits =
     translator: unitType: prefix: service:
+    let
+      # Wire each service's `configData` sources into the primary unit's
+      # `X-Reload-Triggers` so `home-manager switch` restarts it whenever
+      # a config file changes. Preserves any triggers the unit already sets.
+      triggers = configDataSources service;
+      primaryTranslator =
+        if triggers == [ ] then
+          translator
+        else
+          (
+            unit:
+            let
+              ini = translator unit;
+              existing = lib.toList (ini.Unit.X-Reload-Triggers or [ ]);
+            in
+            ini
+            // {
+              Unit = ini.Unit // {
+                X-Reload-Triggers = lib.unique (existing ++ triggers);
+              };
+            }
+          );
+    in
     concatMapAttrs (unitName: unitModule: {
-      "${dashed prefix unitName}" = evalDeferred translator unitModule;
+      "${dashed prefix unitName}" = evalDeferred (
+        if unitName == "" then primaryTranslator else translator
+      ) unitModule;
     }) service.systemd.${unitType}
     // concatMapAttrs (
       subName: subService: makeUnits translator unitType (dashed prefix subName) subService

tests/modules/services-modular/basic.nix

@@ -1,6 +1,6 @@
 { pkgs, ... }:
 {
-  home.services.demo = {
+  home.services."basic" = {
     process.argv = [
       "${pkgs.mpd}/bin/mpd"
       "--no-daemon"
@@ -8,6 +8,6 @@
   };
 
   nmt.script = ''
-    assertFileContent home-files/.config/systemd/user/demo.service ${./demo.service}
+    assertFileContent home-files/.config/systemd/user/basic.service ${./basic.service}
   '';
 }

tests/modules/services-modular/configdata.nix

@@ -10,5 +10,6 @@
 
   nmt.script = ''
     assertFileContent home-files/.config/home-services/demo/config.toml ${./config.toml}
+    assertFileContains home-files/.config/systemd/user/demo.service 'X-Reload-Triggers=/nix/store/'
   '';
 }