Restore user's original Next config.

Author: annajowang

packages/@apphosting/adapter-nextjs/src/bin/build.ts

@@ -9,7 +9,7 @@ import {
 } from "../utils.js";
 import { join } from "path";
 import { getBuildOptions, runBuild } from "@apphosting/common";
-import { addRouteOverrides, overrideNextConfig, validateNextConfigOverride } from "../overrides.js";
+import { addRouteOverrides, overrideNextConfig, restoreNextConfig, validateNextConfigOverride } from "../overrides.js";
 
 const root = process.cwd();
 const opts = getBuildOptions();
@@ -19,29 +19,33 @@ process.env.NEXT_PRIVATE_STANDALONE = "true";
 // Opt-out sending telemetry to Vercel
 process.env.NEXT_TELEMETRY_DISABLED = "1";
 
-const originalConfig = await loadConfig(root, opts.projectDirectory);
+const nextConfig = await loadConfig(root, opts.projectDirectory);
 
 /**
  * Override user's Next Config to optimize the app for Firebase App Hosting
  * and validate that the override resulted in a valid config that Next.js can
  * load.
  *
+ * We restore the user's Next Config at the end of the build, after the config file has been
+ * copied over to the output directory, so that the user's original code is not modified.
+ *
  * If the app does not have a next.config.[js|mjs|ts] file in the first place,
  * then can skip config override.
  *
  * Note: loadConfig always returns a fileName (default: next.config.js) even if
  * one does not exist in the app's root: https://github.com/vercel/next.js/blob/23681508ca34b66a6ef55965c5eac57de20eb67f/packages/next/src/server/config.ts#L1115
  */
-const originalConfigPath = join(root, originalConfig.configFileName);
-if (await exists(originalConfigPath)) {
-  await overrideNextConfig(root, originalConfig.configFileName);
-  await validateNextConfigOverride(root, opts.projectDirectory, originalConfig.configFileName);
+const nextConfigPath = join(root, nextConfig.configFileName);
+if (await exists(nextConfigPath)) {
+  await overrideNextConfig(root, nextConfig.configFileName);
+  await validateNextConfigOverride(root, opts.projectDirectory, nextConfig.configFileName);
 }
 
 await runBuild();
 
+
 const adapterMetadata = getAdapterMetadata();
-const nextBuildDirectory = join(opts.projectDirectory, originalConfig.distDir);
+const nextBuildDirectory = join(opts.projectDirectory, nextConfig.distDir);
 const outputBundleOptions = populateOutputBundleOptions(
   root,
   opts.projectDirectory,
@@ -50,7 +54,7 @@ const outputBundleOptions = populateOutputBundleOptions(
 
 await addRouteOverrides(
   outputBundleOptions.outputDirectoryAppPath,
-  originalConfig.distDir,
+  nextConfig.distDir,
   adapterMetadata,
 );
 
@@ -64,3 +68,5 @@ await generateBuildOutput(
   adapterMetadata,
 );
 await validateOutputDirectory(outputBundleOptions, nextBuildDirectory);
+
+await restoreNextConfig(root, nextConfig.configFileName);

packages/@apphosting/adapter-nextjs/src/overrides.ts

@@ -142,6 +142,34 @@ export async function validateNextConfigOverride(
   }
 }
 
+/**
+ *
+ */
+export async function restoreNextConfig(projectRoot: string, nextConfigFileName: string) {
+  // Check if the file exists in the current working directory
+  const configPath = join(projectRoot, nextConfigFileName);
+  if (!(await exists(configPath))) {
+    return;
+  }
+
+  // Determine the file extension
+  const fileExtension = extname(nextConfigFileName);
+  const originalConfigPath = join(projectRoot, `next.config.original${fileExtension}`);
+  if (!(await exists(originalConfigPath))) {
+    console.warn(`next config may have been overwritten but original contents not found`);
+    return;
+  }
+  console.log(`Restoring original next config in project root`);
+
+  try {
+    await renamePromise(originalConfigPath, configPath);
+  } catch (error) {
+    console.error(`Error restoring Next config: ${error}`);
+  }
+  return;
+
+}
+
 /**
  * Modifies the app's route manifest (routes-manifest.json) to add Firebase App Hosting
  * specific overrides (i.e headers).