Fix: Prevent Slideshow block crash when converting from Gallery (#49606)

[Tejas-Raj01]

Fixes #49606

Proposed changes

• Fixes an editor crash that occurs when transforming a core Gallery block to a Jetpack Slideshow block.
• The Slideshow block's transform logic (extensions/blocks/slideshow/transforms.js) assumed the top-level images attribute would always be populated. However, modern v2 core/gallery blocks store their images in innerBlocks.
• This caused getValidImages( images ) to throw a TypeError: Cannot read properties of undefined (reading 'filter') and crash the editor.
• This PR adds an images = [] default fallback and safely extracts the image data from innerBlocks when the top-level attribute is empty or undefined. (This is identical to the fix we applied for the Tiled Gallery block).

Related product discussion/links

• Discovered by @davemac during the review of the related Tiled Gallery fix. Thanks for the great catch!

Does this pull request change what data or activity we track or use?

• No, this PR does not change any data tracking.

Testing instructions

• Go to any Post or Page in the Block Editor.
• Add a standard WordPress Gallery block and upload or select multiple images.
• Select the Gallery block and click the block icon in the toolbar to Transform to a Slideshow block.
• Before this PR: The editor crashes immediately with a "The editor has encountered an unexpected error" message (TypeError: Cannot read properties of undefined (reading 'filter')).
• After this PR: The Slideshow block renders successfully, cleanly recovering all the images from the Gallery's innerBlocks.

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Jetpack plugin:

The Jetpack plugin has different release cadences depending on the platform:

• WordPress.com Simple releases happen as soon as you deploy your changes after merging this PR (PCYsg-Jjm-p2).
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  • Scheduled release: July 7, 2026
  • Code freeze: July 6, 2026

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[Tejas-Raj01]

Hi @davemac, following up on this one too — this applies the same fix pattern from #50025 to the Slideshow block's transform, including the caption field since Slideshow renders it (unlike Tiled Gallery). CI workflows here are also awaiting approval. Let me know if you'd like any adjustments, or if there's someone else better suited to review this block. Thanks again for catching this!

[davemac]

Same clarification as on #50025 I'm the reporter, not a maintainer, so I can't approve workflows here either. The fix looks right to me though, and including caption makes sense given Slideshow renders it. Hopefully both PRs get picked up from the community queue together, since they're the same root cause.

[jeherve]

This looks great, and thanks for catching the sibling case @davemac :)

Same small thing I flagged over on #50025: the innerBlocks recovery reads attributes.link, but core/image stores its link in href, not link (there's no link attribute on the block). So link will always be undefined here, and image links won't survive the transform. link: attributes.href would recover them. Not a regression since it crashed before, just a chance to make the recovery a bit more complete.

Two tiny nits, neither blocking:

1. getValidImages here didn't pick up the images = [] default that the Tiled Gallery version got. It's fine in practice, since the transform already defaults images = [] before calling it, but the two are slightly inconsistent now.
2. The innerBlocks extraction is duplicated across both PRs; a shared helper might be nice eventually, so a fix like the href one only has to happen in one place.

What do you think?

[Tejas-Raj01]

Hi @jeherve, thanks for the review!

Updates pushed:

• Switched to attributes.href to properly recover links.
• Added the images = [] fallback to getValidImages.

I completely agree on the shared helper—I'll open a follow-up PR to refactor that once these fixes land!