feat: warn if deploying to vercel and any upload collection missing storage adapter (#10391)

A large number of users have been confused why their upload collection
doesn't work as expected when deploying to Vercel. This is because by
default, Payload uses local disk storage for file uploads - which will
not function properly in that environment.

This adds a warning if a user is deploying on Vercel, and they have any
upload collection missing an adapter - aka, writing to disk.

Author: denolfe

packages/payload/src/index.ts

@@ -653,6 +653,20 @@ export class BasePayload {
       )
     }
 
+    // Warn if user is deploying to Vercel, and any upload collection is missing a storage adapter
+    if (process.env.VERCEL) {
+      const uploadCollWithoutAdapter = this.config.collections.filter(
+        (c) => c.upload && c.upload.adapter === undefined, // Uploads enabled, but no storage adapter provided
+      )
+
+      if (uploadCollWithoutAdapter) {
+        const slugs = uploadCollWithoutAdapter.map((c) => c.slug).join(', ')
+        this.logger.warn(
+          `Collections with uploads enabled require a storage adapter when deploying to Vercel. Collections without storage adapters: ${slugs}. See https://payloadcms.com/docs/upload/storage-adapters for more info.`,
+        )
+      }
+    }
+
     this.sendEmail = this.email['sendEmail']
 
     serverInitTelemetry(this)