add generator layers

src/content/ContentBuilder.cpp

@@ -88,5 +88,9 @@ std::unique_ptr<Content> ContentBuilder::build() {
         def->rt.placingBlock = content->blocks.require(def->placingBlock).rt.id;
     }
 
+    for (auto& [name, def] : content->generators.getDefs()) {
+        def->script->prepare(content.get());
+    }
+
     return content;
 }

src/content/ContentLoader.cpp

@@ -473,7 +473,11 @@ void ContentLoader::load() {
 
             auto& def = builder.generators.create(full);
 
-            loadGenerator(def, full, name);
+            try {
+                loadGenerator(def, full, name);
+            } catch (const std::runtime_error& err) {
+                throw std::runtime_error("generator '"+full+"': "+err.what());
+            }
         }
     }