From f9f611fe888fea8556222e7d349c36758e9bf5ca Mon Sep 17 00:00:00 2001
From: Romuald Brillout <git@brillout.com>
Date: Wed, 1 Dec 2021 17:49:24 +0100
Subject: [PATCH] fix: SSR import in development can't resolve default import
 (fix #5706)

---
 packages/vite/src/node/ssr/ssrModuleLoader.ts | 31 ++++++++++++++-----
 1 file changed, 24 insertions(+), 7 deletions(-)

diff --git a/packages/vite/src/node/ssr/ssrModuleLoader.ts b/packages/vite/src/node/ssr/ssrModuleLoader.ts
index 07deb0a44c3a7c..e23998e1af9506 100644
--- a/packages/vite/src/node/ssr/ssrModuleLoader.ts
+++ b/packages/vite/src/node/ssr/ssrModuleLoader.ts
@@ -263,19 +263,15 @@ async function nodeImport(
 
   try {
     const mod = await dynamicImport(url)
-    return proxyESM(id, mod)
+    return proxyESM(mod)
   } finally {
     unhookNodeResolve()
   }
 }
 
 // rollup-style default import interop for cjs
-function proxyESM(id: string, mod: any) {
-  const defaultExport = mod.__esModule
-    ? mod.default
-    : mod.default
-    ? mod.default
-    : mod
+function proxyESM(mod: any) {
+  const defaultExport = getDefaultExport(mod)
   return new Proxy(mod, {
     get(mod, prop) {
       if (prop === 'default') return defaultExport
@@ -283,3 +279,24 @@ function proxyESM(id: string, mod: any) {
     }
   })
 }
+
+function getDefaultExport(mod: any) {
+  if (!('__esModule' in mod)) {
+    // === CJS ===
+    return 'default' in mod ? mod.default : mod
+  } else {
+    // === ESM ===
+    // Unlike CJS, an ESM module can have no default export,
+    // thus we start right away with `mod.default` instead of `mod`.
+    let defaultExport = mod.default
+    const visited = new WeakSet()
+    while ('__esModule' in defaultExport && 'default' in defaultExport) {
+      if (visited.has(defaultExport)) {
+        break
+      }
+      visited.add(defaultExport)
+      defaultExport = defaultExport.default
+    }
+    return defaultExport
+  }
+}