Add transform for group block to cover block.

[getsource]

Description

• Copies inner blocks.
• Uses existing background color or gradient if it's available. Otherwise, defaults to a white background to avoid prompt for image/color.

Initial review props @Mamaduka
Closes: #30445

(edit: removed background default color due to feedback)

How has this been tested?

Tested manually in wp-env, and with existing automated tests with npm run test.

Screenshots

Types of changes

Enhancement.
Adds ability to transform a group block into a cover block, maintaining existing background color or gradient.

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• I've tested my changes with keyboard and screen readers.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR (please manually search all *.native.js files for terms that need renaming or removal).

[getsource]

Thought it was worth noting that I'm not 100% sure about the flow here.
I think it's very useful to allow folks to move from a group to a cover, to allow customizing more.

I decided to have a default background color because otherwise, both the block preview before the transform, and final appearance after transform makes it look like it has removed the group's contents.

Example screenshot, if background color default were removed from the PR, and there is no background or gradient set:
(this is not how it works in the current PR, and only an explanation of the reasoning)

For me, ideally, the placeholder / prompt for the additional data in this case would make it clear that the contents have been migrated -- while still requesting that input. But, not sure if that's something for this issue or not.

Feedback welcome!

[ntsekouras]

Thanks for working on this @getsource, really appreciate it!

I personally believe though that this change will produce more confusion than being an enhancement, and involves opinionated style changes as you already expressed your concerns.

I'll comment on the issue as well, but this functionality doesn't seem to work well. Maybe by having extra checks for having an Image block in group's InnerBlocks and use that as the Cover's background 🤔 ? Even that would need more changes since the isMatch from transforms API would need to be extended to provide the innerBlocks as well and not only the attributes.

Reference: https://developer.wordpress.org/block-editor/reference-guides/block-api/block-transforms/#block

[getsource]

@ntsekouras Updated this to only offer transformation when an existing background color or gradient is available.

[ntsekouras]

Thanks for following this @getsource - nice work 💯

I've left a comment and then is ready to land.

[ntsekouras]

Maybe a rewording here would be good - something like:

Make this transformation available only if the Group has background or gradient set, because otherwise Cover block displays a Placeholder. This helps us avoid arbitrary decisions about the Cover block's background and user confusion about the existence of previous content.

[getsource]

Changed in the most recent commit.

[ntsekouras]

Sorry for all the confusion here @getsource , but this is the final comment and this will be ready to land 😄

[ntsekouras]

Great work! 💯

[getsource]

Thanks so much!