containers: Make declarative containers real systemd services

Without the templating (which is still present for imperative containers), it
will be possible to set individual dependencies. Like depending on the network
only if the hostbridge or hardware interfaces are used.

Ported from #3021

nixos/modules/virtualisation/containers.nix

@@ -278,10 +278,10 @@ in
   };
 
 
-  config = mkIf (config.boot.enableContainers) {
+  config = mkIf (config.boot.enableContainers) (let
 
-    systemd.services."container@" =
-      { description = "Container '%i'";
+    unit = {
+      description = "Container '%i'";
 
       unitConfig.RequiresMountsFor = [ "/var/lib/containers/%i" ];
 
@@ -401,10 +401,6 @@ in
         '';
 
       restartIfChanged = false;
-        #reloadIfChanged = true; # FIXME
-
-        wants = [ "netwprk.target" ];
-        after = [ "network.target" ];
 
       serviceConfig = {
         ExecReload = pkgs.writeScript "reload-container"
@@ -439,6 +435,23 @@ in
         KillSignal = "WINCH";
       };
     };
+  in {
+    systemd.services = listToAttrs (filter (x: x.value != null) (
+      # The generic container template used by imperative containers
+      [{ name = "container@"; value = unit; }]
+      # declarative containers
+      ++ (mapAttrsToList (name: cfg: nameValuePair "container@${name}" (
+        if cfg.autoStart then
+          unit // {
+            wantedBy = [ "multi-user.target" ];
+            wants = [ "network.target" ];
+            after = [ "network.target" ];
+            restartTriggers = [ cfg.path ];
+            reloadIfChanged = true;
+          }
+        else null
+      )) config.containers)
+    ));
 
     # Generate a configuration file in /etc/containers for each
     # container so that container@.target can get the container
@@ -482,31 +495,5 @@ in
     networking.dhcpcd.denyInterfaces = [ "ve-*" ];
 
     environment.systemPackages = [ nixos-container ];
-
-    # Start containers at boot time.
-    systemd.services.all-containers =
-      { description = "All Containers";
-
-        wantedBy = [ "multi-user.target" ];
-
-        unitConfig.ConditionDirectoryNotEmpty = "/etc/containers";
-
-        serviceConfig.Type = "oneshot";
-
-        script =
-          ''
-            res=0
-            shopt -s nullglob
-            for i in /etc/containers/*.conf; do
-              AUTO_START=
-              source "$i"
-              if [ "$AUTO_START" = 1 ]; then
-                systemctl start "container@$(basename "$i" .conf).service" || res=1
-              fi
-            done
-            exit $res
-          ''; # */
-      };
-
-  };
+  });
 }