Dragging multiple images into the editor no longer works with 17.6.0

[mrfoxtalbot]

Description

I find I am unable to drag & drop more than one image into the editor.
One image at a time, it works fine. More than one image, it does not respond.

Step-by-step reproduction instructions

1. Create a new post
2. Select two images in your computer and try to add the to the post by dragging them into it
3. Notice how the editor does not respond.

Screenshots, screen recording, code snippet

I noticed this on a WordPress.com site but I can reproduce it on a self-hosted site using the Gutenberg plugin Version 17.6.0

trim_G5828d.mp4

If I deactivate the plugin and use the core version of the editor (6.4.3), it works as expected

trim_F3qhwa.mp4

Please note that if we add a placeholder Gallery block, it IS possible to drag multiple images.

Screen.Capture.on.2024-02-05.at.00-53-37.mp4

Environment info

• WP 6.4.3 running Twenty Twenty-Three
• Gutenberg plugin v17.6.0

Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

Yes

[t-hamano]

Thanks for the report.

After going back through the commits, it seems that this problem first occurred in #56186, which improved drag and drop. When dragging and dropping multiple images into the editor, the following error is logged in the browser console:

index.js:257 Uncaught TypeError: blocks.map is not a function
    at index.js:257:35

The error is pointing to this line:

gutenberg/packages/block-editor/src/components/use-on-block-drop/index.js

Line 257 in 7a6f458

const blocksClientIds = blocks.map( ( block ) => block.clientId );