Fail more obviously if env vars are missing

Author: banool

src/config.ts

@@ -1,4 +1,4 @@
-type AppConfig = {
+export type AppConfig = {
   CONFIDENTIAL_ASSET_MODULE_ADDR: string;
   /**
    * This is the asset the user deals with in the app. For the demo they only use a
@@ -58,3 +58,11 @@ export const appConfig: AppConfig = {
 
   FORCE_MAINTENANCE_PAGE: process.env.FORCE_MAINTENANCE_PAGE === 'true',
 };
+
+// Iterate through the config and ensure nothing is undefined. This check runs client
+// side, so we only check NEXT_PUBLIC_ variables. We check everything in middleware.ts.
+for (const key in appConfig) {
+  if (key.startsWith('NEXT_PUBLIC_') && appConfig[key as keyof AppConfig] === undefined) {
+    throw new Error(`Required environment variable ${key} is not set.`);
+  }
+}

src/middleware.ts

@@ -1,7 +1,14 @@
 import { createMiddleware, type MiddlewareFunctionProps } from '@rescale/nemo';
 import { NextResponse } from 'next/server';
 
-import { appConfig } from './config';
+import { AppConfig, appConfig } from './config';
+
+// Iterate through the config and ensure nothing is undefined.
+for (const key in appConfig) {
+  if (appConfig[key as keyof AppConfig] === undefined) {
+    throw new Error(`Required environment variable ${key} is not set.`);
+  }
+}
 
 async function shouldShowMaintenancePage() {
   if (appConfig.FORCE_MAINTENANCE_PAGE) {