feat(remix-dev): add warning for v2 "cjs"->"esm" defaults (#6154)

Author: jacob-ebey

integration/hmr-test.ts

@@ -17,6 +17,7 @@ let fixture = (options: {
   files: {
     "remix.config.js": js`
       module.exports = {
+        serverModuleFormat: "cjs",
         tailwind: true,
         future: {
           unstable_dev: {

packages/remix-dev/__tests__/create-test.ts

@@ -13,6 +13,7 @@ import {
   flatRoutesWarning,
   formMethodWarning,
   metaWarning,
+  serverModuleFormatWarning,
 } from "../config";
 
 beforeAll(() => server.listen({ onUnhandledRequest: "error" }));
@@ -359,6 +360,8 @@ describe("the create command", () => {
         "\n" +
         metaWarning +
         "\n" +
+        serverModuleFormatWarning +
+        "\n" +
         flatRoutesWarning +
         "\n\n" +
         getOptOutOfInstallMessage() +

packages/remix-dev/config.ts

@@ -455,6 +455,11 @@ export async function readConfig(
   let serverEntryPoint = appConfig.server;
   let serverMainFields = appConfig.serverMainFields;
   let serverMinify = appConfig.serverMinify;
+
+  if (!appConfig.serverModuleFormat) {
+    warnOnce(serverModuleFormatWarning, "serverModuleFormatWarning")
+  }
+
   let serverModuleFormat = appConfig.serverModuleFormat || "cjs";
   let serverPlatform = appConfig.serverPlatform || "node";
   if (isCloudflareRuntime) {
@@ -895,6 +900,12 @@ export let serverBuildTargetWarning =
   "For instructions on making this change see " +
   "https://remix.run/docs/en/v1.15.0/pages/v2#serverbuildtarget";
 
+export const serverModuleFormatWarning =
+  "⚠️ REMIX FUTURE CHANGE: The `serverModuleFormat` config default option will be changing in v2 " +
+  "from `cjs` to `esm`. You can prepare for this change by explicitly specifying `serverModuleFormat: 'cjs'`. " +
+  "For instructions on making this change see " +
+  "https://remix.run/docs/en/v1.16.0/pages/v2#servermoduleformat";
+
 export let flatRoutesWarning =
   "⚠️ REMIX FUTURE CHANGE: The route file convention is changing in v2. " +
   "You can prepare for this change at your convenience with the `v2_routeConvention` future flag. " +