perf: cache loader dynamic imports

src/cachedImport.ts

@@ -0,0 +1,12 @@
+/** Share the pending import while allowing a failed import to be retried. */
+export const cachedImport = <T>(
+  importer: () => Promise<T>,
+): (() => Promise<T>) => {
+  let promise: Promise<T> | undefined;
+
+  return () =>
+    (promise ??= importer().catch((error: unknown) => {
+      promise = undefined;
+      throw error;
+    }));
+};

src/jiti.ts

@@ -1,6 +1,9 @@
+import { cachedImport } from './cachedImport.js';
 import { getConfigExport } from './helpers.js';
 import type { ConfigDefinition, LoadedConfig } from './types.js';
 
+const getJiti = cachedImport(() => import('jiti'));
+
 export const loadWithJiti = async <Config, Params extends unknown[]>(
   configPath: string,
   exportName: string | false,
@@ -9,7 +12,7 @@ export const loadWithJiti = async <Config, Params extends unknown[]>(
   let createJiti: (typeof import('jiti'))['createJiti'];
 
   try {
-    ({ createJiti } = await import('jiti'));
+    ({ createJiti } = await getJiti());
   } catch (error) {
     throw new Error(
       'The "jiti" package is required to load this config. Install it with your package manager.',

src/native.ts

@@ -1,4 +1,9 @@
 import { pathToFileURL } from 'node:url';
+import { cachedImport } from './cachedImport.js';
+
+const getFreshImport = cachedImport(
+  () => import(/* rspackChunkName: 'freshImport' */ 'fresh-import'),
+);
 
 type NativeLoadResult = {
   configModule: unknown;
@@ -21,10 +26,7 @@ export const loadWithNative = async (
     };
   }
 
-  const { freshImport } = await import(
-    /* rspackChunkName: 'freshImport' */
-    'fresh-import'
-  );
+  const { freshImport } = await getFreshImport();
   const freshImportResult = await freshImport(configFileURL);
 
   if (freshImportResult) {