Group block: When in its initial setup state, it's not a container and can't be dragged into

[jasmussen]

When a group block is inserted empty, it comes with a setup state allowing you to choose between the default flow group, a row, and a stack variation. In this state, the group looks like a group container in the list view, but it isn't, so I cannot drag any blocks into this container. GIF showing this:

Filing this as a bug, as I would expect dragging a block into the group, even in its setup state, to have the dragged block nest under it.

Related: #39064

[richtabor]

100%. This seems an easy win.

[andrewserong]

I did a little digging into this one, and it's a little more complex than I realised at first glance. Just jotting down a few technical notes. Feel free to ignore these, but I thought I'd write them down in case it helps anyone else looking. If no-one beats me to it, I'll look at seeing if I can put up a fix next week!

• The list view calls canInsertBlocks here to determine whether to allow the dragged blocks as children.
• Then the canInsertBlockTypeUnmemoized function checks getBlockListSettings for the Group block here. A Group block that is in its placeholder state has no entry in the block list settings.
• When a Group block is in its placeholder state, it doesn't render out the result from useInnerBlocksProps, which means that InnerBlocks is never rendered.
• InnerBlocks is responsible for calling useNestedSettingsUpdate here which calls updateBlockListSettings here. This is how a block that renders its inner blocks winds up with an entry in the block list settings.

So, long story short — I think if we were to try moving the call to useNestedSettingsUpdate up so that it gets called when useInnerBlocksProps is used, instead of when InnerBlocks is rendered, then we might be able to get the block list settings updated for container blocks when they're inserted / in their placeholder state, rather than just when they already have inner blocks. That's my idea at the moment, anyway 🙂

[andrewserong]

I've got a fix up in #49361 — it works by ensuring that useInnerBlocksProps and its children are output when the block is in the placeholder state. Seems to work pretty well so far 🤞