feat: use auto config loader with bundled jiti

packages/rstack/src/config.ts

@@ -1,5 +1,5 @@
 import { AsyncLocalStorage } from 'node:async_hooks';
-import { loadConfig } from '@rstackjs/load-config';
+import { loadConfig, setJitiLoader } from '@rstackjs/load-config';
 import type {
   defineConfig as defineAppConfig,
   RsbuildConfigDefinition,
@@ -15,6 +15,23 @@ import type { FmtConfigDefinition } from './fmt/types.ts';
 import type { StagedConfig } from './staged.ts';
 import { composeConfigLayers, flattenConfigLayers } from './configLayers.ts';
 
+setJitiLoader(async () => {
+  const { createJiti } = await import('@rsbuild/core/jiti');
+
+  return {
+    createJiti: (...args: Parameters<typeof createJiti>) => {
+      const session = getConfigSessionStorage().getStore();
+      if (session?.active) {
+        // A native attempt may have registered configs before falling back.
+        // Reset per attempt, since the jiti importer itself is cached.
+        session.configs = {};
+        session.extends = undefined;
+      }
+      return createJiti(...args);
+    },
+  };
+});
+
 export type RspressConfigDefinition = UserConfig | UserConfigAsyncFn;
 
 type RslintConfigFactory = (
@@ -254,7 +271,7 @@ export const loadRstackConfig = async ({
   return getConfigSessionStorage().run(session, async () => {
     try {
       const { filePath, dependencies } = await loadConfig({
-        loader: 'native',
+        loader: 'auto',
         exportName: false,
         fresh: true,
         cwd,

packages/rstack/tests/config/load-config/fallback.config.ts

@@ -0,0 +1,6 @@
+import { define } from 'rstack';
+
+define.extends([{ fmt: { singleQuote: true } }]);
+define.lib({});
+
+await import('./jiti.config.ts');

packages/rstack/tests/config/load-config/index.test.ts

@@ -58,6 +58,24 @@ test('should prefer an explicit config path over the state config path', async (
   expect(filePath).toBe(explicitConfigPath);
 });
 
+test('should fall back to jiti for TypeScript syntax unsupported by the native loader', async () => {
+  const { configs } = await loadConfigFile('jiti.config.ts');
+
+  expect(configs.app).toEqual({ html: { title: 'jiti config' } });
+});
+
+test('should avoid duplicate definitions when falling back to jiti across repeated loads', async () => {
+  for (let attempt = 0; attempt < 2; attempt++) {
+    const { configs } = await loadConfigFile('fallback.config.ts');
+
+    expect(configs).toEqual({
+      app: { html: { title: 'jiti config' } },
+      lib: {},
+      fmt: { singleQuote: true },
+    });
+  }
+});
+
 test('should resolve a relative explicit config path from cwd', async () => {
   const { configs, filePath } = await loadRstackConfig({
     configFilePath: 'explicit.config.ts',

packages/rstack/tests/config/load-config/jiti.config.ts

@@ -0,0 +1,7 @@
+import { define } from 'rstack';
+
+enum Title {
+  App = 'jiti config',
+}
+
+define.app({ html: { title: Title.App } });