feat(module/workflow): Add a header to the start of generated files

modules/workflows.nix

@@ -25,6 +25,7 @@ let
     attrsOf
     bool
     enum
+    lines
     path
     str
     ;
@@ -34,7 +35,13 @@ let
   cfg = config;
 
   generate =
-    name: value:
+    name:
+    {
+
+      buildCheck,
+      rootSrc,
+      value,
+    }:
     runCommand "${name}.yaml"
       {
         nativeBuildInputs = [
@@ -43,21 +50,29 @@ let
         ];
 
         value = builtins.toJSON value;
-        passAsFile = [ "value" ];
+        inherit (cfg) header;
+        passAsFile = [
+          "header"
+          "value"
+        ];
         preferLocalBuild = true;
       }
       ''
-        json2yaml "$valuePath" "$out"
-
-        # Check that the workflow is valid
-        cd "${cfg.rootSrc}" && action-validator "$out"
-      '';
+        json2yaml "$valuePath" out
+        cat "$headerPath" out > "$out"
+      ''
+    + (optionalString buildCheck ''
+      # Check that the workflow is valid
+      cd "${rootSrc}" && action-validator "$out"
+    '');
 
   install =
     name: value:
     let
-      result =
-        if cfg.buildCheck then generate name value else (pkgs.formats.yaml { }).generate name value;
+      result = generate name {
+        inherit value;
+        inherit (cfg) buildCheck rootSrc;
+      };
       path = ".${cfg.platform}/workflows/${name}.yaml";
     in
     ''
@@ -121,6 +136,17 @@ in
         It introduces a dependency on the `rootSrc` directory.
       '';
     };
+
+    header = mkOption {
+      type = lines;
+      default = ''
+        ###
+        # This file was automatically generated with nix-actions.
+      '';
+      description = ''
+        Text header to prepend to the generated workflow YAML file.
+      '';
+    };
   };
 
   config = {