start without config file, improve error messaging on faulty config

packages/core/src/build/hook/build.js

@@ -8,6 +8,7 @@ import join from "@rcompat/fs/join";
 import exclude from "@rcompat/object/exclude";
 import stringify from "@rcompat/object/stringify";
 import manifest from "@rcompat/package/manifest";
+import root from "@rcompat/package/root";
 import copy_includes from "./copy_includes.js";
 import $router from "./router.js";
 
@@ -163,7 +164,12 @@ const post = async (app, mode, target) => {
   await write_bootstrap(build_number, app, mode);
 
   // copy config file
-  await app.root.join(config_filename).copy(app.path.build.join(config_filename));
+  const local_config = app.root.join(config_filename);
+  const build_config = app.path.build.join(config_filename);
+  const root_base = await root(import.meta.url);
+  const default_config = root_base.join("/src/private/config.js");
+  (await local_config.exists() ? local_config : default_config)
+    .copy(build_config);
 
   const manifest_data = await manifest();
   // create package.json

packages/core/src/build/index.js

@@ -12,18 +12,27 @@ import platform from "@rcompat/platform";
 import app from "./app.js";
 import { build, init } from "./hook/exports.js";
 
+const empty_config = config => config === undefined || empty(config);
+
 const get_config = async project_root => {
   const local_config = project_root.join(config_filename);
-  return await local_config.exists()
-    ? tryreturn(async _ => {
+  const exists = await local_config.exists()
+  if (exists) {
+    try {
       const imported = await local_config.import("default");
 
-      empty(imported) && empty_config_file(local_config);
+      empty_config(imported) && empty_config_file(local_config);
 
       return imported;
-    }).orelse(({ message }) =>
-      error_in_config_file(message, `${platform} ${local_config}`))
-    : config;
+    } catch (error) {
+      if (error.level === undefined) {
+        error_in_config_file(error.message, `${platform} ${local_config}`);
+      } else {
+        throw error;
+      }
+    }
+  }
+  return config;
 };
 
 export default async (mode, target) => tryreturn(async _ => {