fix: custom incremental cache handlers should work when transpiled (v…

…ercel#54472)

This fixes a `CurCacheHandler is not a constructor` error when the custom cache handler path is transpiled from ESM -> CJS (resulting in the handler being attached to the `default` property on the module's exports)

Closes NEXT-1558
Fixes vercel#54453

packages/next/src/build/index.ts

@@ -1278,6 +1278,7 @@ export default async function build(
         CacheHandler = require(path.isAbsolute(incrementalCacheHandlerPath)
           ? incrementalCacheHandlerPath
           : path.join(dir, incrementalCacheHandlerPath))
+        CacheHandler = CacheHandler.default || CacheHandler
       }
 
       const { ipcPort, ipcValidationKey } = await initialize({

test/e2e/app-dir/app-static/app-static-custom-cache-handler-esm.test.ts

@@ -0,0 +1,27 @@
+import { createNextDescribe } from 'e2e-utils'
+import { join } from 'path'
+
+createNextDescribe(
+  'app-static-custom-cache-handler-esm',
+  {
+    files: __dirname,
+    env: {
+      CUSTOM_CACHE_HANDLER: join(
+        __dirname,
+        './cache-handler-default-export.js'
+      ),
+    },
+  },
+  ({ next, isNextStart }) => {
+    if (!isNextStart) {
+      it('should skip', () => {})
+      return
+    }
+
+    it('should have logs from cache-handler', async () => {
+      expect(next.cliOutput).toContain('initialized custom cache-handler')
+      expect(next.cliOutput).toContain('cache-handler get')
+      expect(next.cliOutput).toContain('cache-handler set')
+    })
+  }
+)

test/e2e/app-dir/app-static/app-static-custom-handler.test.ts

@@ -1,2 +1,2 @@
-process.env.CUSTOM_CACHE_HANDLER = '1'
+process.env.CUSTOM_CACHE_HANDLER = require.resolve('./cache-handler.js')
 require('./app-static.test')

test/e2e/app-dir/app-static/cache-handler-default-export.js

@@ -0,0 +1,26 @@
+Object.defineProperty(exports, '__esModule', { value: true })
+
+const cache = new Map()
+
+var CacheHandler = /** @class */ (function () {
+  function CacheHandler(options) {
+    this.options = options
+    this.cache = cache
+    console.log('initialized custom cache-handler')
+  }
+  CacheHandler.prototype.get = function (key) {
+    console.log('cache-handler get', key)
+    return Promise.resolve(this.cache.get(key))
+  }
+  CacheHandler.prototype.set = function (key, data) {
+    console.log('cache-handler set', key)
+    this.cache.set(key, {
+      value: data,
+      lastModified: Date.now(),
+    })
+    return Promise.resolve(undefined)
+  }
+  return CacheHandler
+})()
+
+exports.default = CacheHandler

test/e2e/app-dir/app-static/next.config.js

@@ -2,9 +2,7 @@
 module.exports = {
   experimental: {
     logging: 'verbose',
-    incrementalCacheHandlerPath: process.env.CUSTOM_CACHE_HANDLER
-      ? require.resolve('./cache-handler.js')
-      : undefined,
+    incrementalCacheHandlerPath: process.env.CUSTOM_CACHE_HANDLER,
   },
   // assetPrefix: '/assets',
   rewrites: async () => {