implement next config override logic to import in existing config and export overrided config

Author: mathu97

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

@@ -8,7 +8,7 @@ import {
 } from "../utils.js";
 import { join } from "path";
 import { getBuildOptions, runBuild } from "@apphosting/common";
-import { addRouteOverrides } from "../overrides.js";
+import { addRouteOverrides, overrideNextConfig } from "../overrides.js";
 
 const root = process.cwd();
 const opts = getBuildOptions();
@@ -22,7 +22,7 @@ if (!process.env.FRAMEWORK_VERSION) {
 }
 
 const { distDir, configFileName } = await loadConfig(root, opts.projectDirectory);
-
+await overrideNextConfig(configFileName);
 await runBuild();
 
 const adapterMetadata = getAdapterMetadata();

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

@@ -1,7 +1,80 @@
 import { AdapterMetadata, MiddlewareManifest } from "./interfaces.js";
-import { loadRouteManifest, writeRouteManifest, loadMiddlewareManifest } from "./utils.js";
+import {
+  loadRouteManifest,
+  writeRouteManifest,
+  loadMiddlewareManifest,
+  exists,
+  writeFile,
+} from "./utils.js";
+import { join } from "path";
+import { readFileSync } from "fs";
 
-export async function overrideNextConfig(nextConfigFileName: string) {}
+export async function overrideNextConfig(nextConfigFileName: string) {
+  // Check if the file exists in the current working directory
+  const cwd = process.cwd();
+  const configPath = join(cwd, nextConfigFileName);
+
+  if (!(await exists(configPath))) {
+    console.log(`No Next.js config file found at ${configPath}`);
+    return;
+  }
+
+  // Determine the file extension
+  const fileExtension = nextConfigFileName.split(".").pop() || "js";
+  const originalConfigName = `next.config.original.${fileExtension}`;
+  const newConfigName = `next.config.${fileExtension}`;
+
+  // Rename the original config file
+  try {
+    const originalContent = readFileSync(configPath, "utf-8");
+    await writeFile(join(cwd, originalConfigName), originalContent);
+
+    // Create a new config file with the appropriate import
+    let importStatement;
+    if (fileExtension === "js" || fileExtension === "cjs") {
+      importStatement = `const originalConfig = require('./${originalConfigName}');`;
+    } else if (fileExtension === "mjs") {
+      importStatement = `import originalConfig from './${originalConfigName}';`;
+    } else if (fileExtension === "ts") {
+      importStatement = `import originalConfig from './${originalConfigName.replace(".ts", "")}';`;
+    } else {
+      throw new Error(`Unsupported file extension: ${fileExtension}`);
+    }
+
+    // Create the new config content with our overrides
+    const newConfigContent = `${importStatement}
+
+// This file was automatically generated by Firebase App Hosting adapter
+const config = typeof originalConfig === 'function' 
+  ? (...args) => {
+      const resolvedConfig = originalConfig(...args);
+      return {
+        ...resolvedConfig,
+        images: {
+          ...(resolvedConfig.images || {}),
+          unoptimized: true,
+        },
+      };
+    }
+  : {
+      ...originalConfig,
+      images: {
+        ...(originalConfig.images || {}),
+        unoptimized: true,
+      },
+    };
+
+${fileExtension === "mjs" ? "export default config;" : "module.exports = config;"}
+`;
+
+    // Write the new config file
+    await writeFile(join(cwd, newConfigName), newConfigContent);
+    console.log(`Successfully created ${newConfigName} with Firebase App Hosting overrides`);
+  } catch (error) {
+    console.error(`Error overriding Next.js config: ${error}`);
+    throw error;
+  }
+}
 
 /**
  * Modifies the app's route manifest (routes-manifest.json) to add Firebase App Hosting