Work around issue with next externals

Author: benjie

@app/client/src/next.config.js

@@ -41,6 +41,27 @@ if (!ROOT_URL) {
       webpack(config, { webpack, dev, isServer }) {
         if (dev) config.devtool = "cheap-module-source-map";
 
+        const makeSafe = externals => {
+          if (Array.isArray(externals)) {
+            return externals.map(ext => {
+              if (typeof ext === "function") {
+                return (context, request, callback) => {
+                  if (/^@app\//.test(request)) {
+                    callback();
+                  } else {
+                    return ext(context, request, callback);
+                  }
+                };
+              } else {
+                return ext;
+              }
+            });
+          }
+        };
+
+        const externals =
+          isServer && dev ? makeSafe(config.externals) : config.externals;
+
         return {
           ...config,
           plugins: [
@@ -51,7 +72,7 @@ if (!ROOT_URL) {
             }),
           ],
           externals: [
-            ...(config.externals || []),
+            ...(externals || []),
             isServer ? { "pg-native": "pg/lib/client" } : null,
           ].filter(_ => _),
         };