fix(remix-dev): allow serverBuildPath to end with .cjs

.changeset/wild-steaks-bathe.md

@@ -0,0 +1,7 @@
+---
+"@remix-run/dev": patch
+---
+
+Fix server builds where serverBuildPath extension is `.cjs`.
+
+Fix a bug that caused the server build file to be emitted into the assets directory if the value of `serverBuildPath` ended in `.cjs`.

integration/compiler-mjs-cjs-output-test.ts

@@ -0,0 +1,35 @@
+import { test, expect } from "@playwright/test";
+import * as fs from "node:fs";
+import * as path from "node:path";
+
+import { createFixtureProject, js } from "./helpers/create-fixture.js";
+
+test.describe("", () => {
+  for (let [serverModuleExt, serverModuleFormat, exportStatement] of [
+    ["mjs", "esm", "export {"],
+    ["cjs", "cjs", "module.exports ="],
+  ]) {
+    test(`can write .${serverModuleExt} server output module`, async () => {
+      let projectDir = await createFixtureProject({
+        files: {
+          // Ensure the config is valid ESM
+          "remix.config.js": js`
+            export default {
+              serverModuleFormat: "${serverModuleFormat}",
+              serverBuildPath: "build/index.${serverModuleExt}",
+            };
+          `,
+        },
+      });
+
+      let buildPath = path.resolve(
+        projectDir,
+        "build",
+        `index.${serverModuleExt}`
+      );
+      expect(fs.existsSync(buildPath), "doesn't exist").toBe(true);
+      let contents = fs.readFileSync(buildPath, "utf8");
+      expect(contents, "no export statement").toContain(exportStatement);
+    });
+  }
+});

packages/remix-dev/compiler/server/write.ts

@@ -11,7 +11,7 @@ export async function write(
   await fse.ensureDir(path.dirname(config.serverBuildPath));
 
   for (let file of outputFiles) {
-    if (file.path.endsWith(".js") || file.path.endsWith(".mjs")) {
+    if ([".js", ".cjs", ".mjs"].some((ext) => file.path.endsWith(ext))) {
       // fix sourceMappingURL to be relative to current path instead of /build
       let filename = file.path.substring(file.path.lastIndexOf(path.sep) + 1);
       let escapedFilename = filename.replace(/\./g, "\\.");