Add build.extendedInfo to service

To let services write to the x-arion section.

src/nix/eval-composition.nix

@@ -21,6 +21,7 @@ let
     ./modules/composition/docker-compose.nix
     ./modules/composition/host-environment.nix
     ./modules/composition/images.nix
+    ./modules/composition/service-info.nix
   ];
 
   argsModule = {

src/nix/eval-service.nix

@@ -10,6 +10,7 @@ let
   builtinModules = [
     argsModule
     ./modules/service/docker-compose-service.nix
+    ./modules/service/extended-info.nix
     ./modules/service/host-store.nix
     ./modules/service/host.nix
     ./modules/service/image.nix

src/nix/modules/composition/docker-compose.nix

@@ -26,7 +26,11 @@ in
     };
     docker-compose.raw = lib.mkOption {
       type = lib.types.attrs;
-      description = "Nested attribute set that will be turned into the docker-compose.yaml file, using Nix's toJSON builtin.";
+      description = "Attribute set that will be turned into the docker-compose.yaml file, using Nix's toJSON builtin.";
+    };
+    docker-compose.extended = lib.mkOption {
+      type = lib.types.attrs;
+      description = "Attribute set that will be turned into the x-arion section of the docker-compose.yaml file.";
     };
     docker-compose.services = lib.mkOption {
       default = {};
@@ -47,6 +51,7 @@ in
     docker-compose.raw = {
       version = "3.4";
       services = lib.mapAttrs (k: c: c.config.build.service) config.docker-compose.evaluatedServices;
+      x-arion = config.docker-compose.extended;
     };
   };
 }

src/nix/modules/composition/images.nix

@@ -31,6 +31,6 @@ in
   };
   config = {
     build.imagesToLoad = lib.attrValues serviceImages;
-    docker-compose.raw.x-arion.images = config.build.imagesToLoad;
+    docker-compose.extended.images = config.build.imagesToLoad;
   };
 }

src/nix/modules/composition/service-info.nix

@@ -0,0 +1,24 @@
+/*
+   Adds extendedInfo from services to the Docker Compose file.
+
+   This contains fields that are not in Docker Compose schema.
+ */
+{ config, lib, ... }:
+let
+  serviceInfo =
+    lib.mapAttrs getInfo (
+      lib.filterAttrs filterFunction config.docker-compose.evaluatedServices
+    );
+
+  filterFunction = _serviceName: service:
+    # shallow equality suffices for emptiness test
+    builtins.attrNames service.config.build.extendedInfo != [];
+
+  getInfo = _serviceName: service: service.config.build.extendedInfo;
+
+in
+{
+  config = {
+    docker-compose.extended.serviceInfo = serviceInfo;
+  };
+}

src/nix/modules/service/extended-info.nix

@@ -0,0 +1,20 @@
+{ config, lib, ... }:
+let
+  inherit (lib) mkOption;
+  inherit (lib.types) attrsOf unspecified;
+in
+{
+  options = {
+    build.extendedInfo = mkOption {
+      type = attrsOf unspecified;
+      description = ''
+        Information about a service to include in the Docker Compose file,
+        but that will not be used by the <code>docker-compose</code> command
+        itself.
+
+        It will be inserted in <code>x-arion.serviceInfo.&lt;service.name></code>.
+      '';
+      default = {};
+    };
+  };
+}