Better types

packages/nextjs/src/server/cache-instrumentation.ts

@@ -1,7 +1,6 @@
 import { startSpan } from '@sentry/node';
 // We need to import `* as` due to Rollup cjs interop issues
 import * as iitm from 'import-in-the-middle';
-import type { HookFn } from 'import-in-the-middle';
 
 type CacheHandlerClass = {
   new (options: unknown): CacheHandlerClass;
@@ -10,18 +9,28 @@ type CacheHandlerClass = {
   revalidateTag(tag: string): Promise<void>;
 };
 
+function looksLikeCacheHandlerClass(obj: unknown): obj is CacheHandlerClass {
+  return (
+    typeof obj === 'function' && typeof obj.prototype === 'object' && 'get' in obj.prototype && 'set' in obj.prototype
+  );
+}
+
 /**
  * Hooks the loading of the cache handler module at the `cacheHandlerPath` and wraps the class to add cache spans around
  * the get and set methods.
  */
 export function enableCacheInstrumentation(cacheHandlerPath: string): void {
   // We only hook the specific path of the cache handler module
-  new iitm.Hook([cacheHandlerPath], ((exports: { default: CacheHandlerClass }) => {
+  new iitm.Hook([cacheHandlerPath], exports => {
+    if (!looksLikeCacheHandlerClass(exports.default)) {
+      return;
+    }
+
     // Grab the existing default export which should be the user defined cache handler
     const UserCache = exports.default;
 
     // Define a new class that extends the user defined cache handler
-    class CacheHandler extends UserCache {
+    class SentryCacheHandlerWrapper extends UserCache {
       public constructor(options: unknown) {
         super(options);
       }
@@ -56,6 +65,6 @@ export function enableCacheInstrumentation(cacheHandlerPath: string): void {
     }
 
     // Overwrite the default export with the new CacheHandler class
-    exports.default = CacheHandler;
-  }) as unknown as HookFn);
+    exports.default = SentryCacheHandlerWrapper;
+  });
 }