1 files changed, 57 insertions, 0 deletions
diff --git a/packages/integrations/vercel/src/lib/fs.ts b/packages/integrations/vercel/src/lib/fs.ts
index 64c4c69ba..47b218ce5 100644
--- a/packages/integrations/vercel/src/lib/fs.ts
+++ b/packages/integrations/vercel/src/lib/fs.ts
@@ -1,5 +1,7 @@
 import type { PathLike } from 'node:fs';
 import * as fs from 'node:fs/promises';
+import nodePath from 'node:path';
+import { fileURLToPath } from 'node:url';
 
 export async function writeJson<T>(path: PathLike, data: T) {
 	await fs.writeFile(path, JSON.stringify(data), { encoding: 'utf-8' });
@@ -15,3 +17,58 @@ export async function emptyDir(dir: PathLike): Promise<void> {
 }
 
 export const getVercelOutput = (root: URL) => new URL('./.vercel/output/', root);
+
+/**
+ * Copies files into a folder keeping the folder structure intact.
+ * The resulting file tree will start at the common ancestor.
+ *
+ * @param {URL[]} files A list of files to copy (absolute path).
+ * @param {URL} outDir Destination folder where to copy the files to (absolute path).
+ * @param {URL[]} [exclude] A list of files to exclude (absolute path).
+ * @returns {Promise<string>} The common ancestor of the copied files.
+ */
+export async function copyFilesToFunction(
+	files: URL[],
+	outDir: URL,
+	exclude: URL[] = []
+): Promise<string> {
+	const excludeList = exclude.map(fileURLToPath);
+	const fileList = files.map(fileURLToPath).filter((f) => !excludeList.includes(f));
+
+	if (files.length === 0) throw new Error('[@astrojs/vercel] No files found to copy');
+
+	let commonAncestor = nodePath.dirname(fileList[0]);
+	for (const file of fileList.slice(1)) {
+		while (!file.startsWith(commonAncestor)) {
+			commonAncestor = nodePath.dirname(commonAncestor);
+		}
+	}
+
+	for (const origin of fileList) {
+		const dest = new URL(nodePath.relative(commonAncestor, origin), outDir);
+
+		const realpath = await fs.realpath(origin);
+		const isSymlink = realpath !== origin;
+		const isDir = (await fs.stat(origin)).isDirectory();
+
+		// Create directories recursively
+		if (isDir && !isSymlink) {
+			await fs.mkdir(new URL('..', dest), { recursive: true });
+		} else {
+			await fs.mkdir(new URL('.', dest), { recursive: true });
+		}
+
+		if (isSymlink) {
+			const realdest = fileURLToPath(new URL(nodePath.relative(commonAncestor, realpath), outDir));
+			await fs.symlink(
+				nodePath.relative(fileURLToPath(new URL('.', dest)), realdest),
+				dest,
+				isDir ? 'dir' : 'file'
+			);
+		} else if (!isDir) {
+			await fs.copyFile(origin, dest);
+		}
+	}
+
+	return commonAncestor;
+}