Forms: fix Show summary toggle on blocks with legacy customThankyou

[enejb]

Fixes #

Proposed changes

• Rewrite the customThankyou migration useEffect in edit.tsx so it (a) clears customThankyou to '' in the same setAttributes call that writes the modern attribute, and (b) only depends on customThankyou itself — not disableSummary / confirmationType.

Why

The previous useEffect (added in #46866) re-fired every time customThankyou, confirmationType, or disableSummary changed. For a block saved with customThankyou: "noSummary":

1. On load, the effect saw customThankyou === 'noSummary' && !disableSummary, called setAttributes({ disableSummary: true }), but left customThankyou in place.
2. The user flipped the "Show summary" toggle → disableSummary became false.
3. The effect re-ran with the same condition still true → forced disableSummary: true again → toggle reverted.

The fix is small: on the first render that sees a legacy customThankyou, clear it (customThankyou: '') in the same update that sets disableSummary / confirmationType. customThankyou === '' is the default, so after that first update the condition is permanently false and nothing re-fires on subsequent user toggles. setAttributes also properly dirties the post, so the cleaned attributes actually persist on save.

PHP backward-compat fallbacks in class-contact-form.php are left in place so posts whose post_content still has customThankyou (never re-opened in the editor) keep rendering correctly on the frontend.

Related product discussion/links

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

No.

Testing instructions

1. In a fresh post, add a Jetpack Form block via the inserter.
2. Switch to Code Editor and edit the form block's opening comment to include the legacy attribute, e.g.:

   <!-- wp:jetpack/contact-form {"customThankyou":"noSummary","subject":"Test"} -->
   ...existing inner blocks...
   <!-- /wp:jetpack/contact-form -->

3. Switch back to Visual Editor. The migration runs immediately: customThankyou is cleared and disableSummary: true is set. Save the post, then reload. Re-open Code Editor — customThankyou is gone from the comment and "disableSummary":true is present.
4. In the sidebar under "Confirmation", "Show summary" is off. Toggle it on. It stays on across saves and reloads. On trunk today the toggle flicks back immediately.
5. Repeat with "customThankyou":"redirect" — migration sets confirmationType: "redirect" and the Redirect URL field appears.
6. Repeat with "customThankyou":"message" — migrates to disableSummary: true (same behaviour as noSummary).
7. A fresh form block behaves normally; the migration branch doesn't fire.
8. Frontend: a post whose stored post_content still has customThankyou: "noSummary" (never re-opened in the editor) continues to hide the summary on render — the PHP fallback in class-contact-form.php is intentionally kept.

[github-actions]

Are you an Automattician? Please test your changes on all WordPress.com environments to help mitigate accidental explosions.

• To test on WoA, go to the Plugins menu on a WoA dev site. Click on the "Upload" button and follow the upgrade flow to be able to upload, install, and activate the Jetpack Beta plugin. Once the plugin is active, go to Jetpack > Jetpack Beta, select your plugin (Jetpack), and enable the fix/noSummary-bug-form branch.
• To test on Simple, run the following command on your sandbox:

bin/jetpack-downloader test jetpack fix/noSummary-bug-form

Interested in more tips and information?

• In your local development environment, use the jetpack rsync command to sync your changes to a WoA dev blog.
• Read more about our development workflow here: PCYsg-eg0-p2
• Figure out when your changes will be shipped to customers here: PCYsg-eg5-p2

[github-actions]

Thank you for your PR!

When contributing to Jetpack, we have a few suggestions that can help us test and review your patch:

• ✅ Include a description of your PR changes.
  
• ✅ Add a "[Status]" label (In Progress, Needs Review, ...).
  
• ✅ Add testing instructions.
  
• ✅ Specify whether this PR includes any changes to data or privacy.
  
• ✅ Add changelog entries to affected projects
  

This comment will be updated as you work on your PR and make changes. If you think that some of those checks are not needed for your PR, please explain why you think so. Thanks for cooperation 🤖

---

Follow this PR Review Process:

1. Ensure all required checks appearing at the bottom of this PR are passing.
2. Make sure to test your changes on all platforms that it applies to. You're responsible for the quality of the code you ship.
3. You can use GitHub's Reviewers functionality to request a review.
4. When it's reviewed and merged, you will be pinged in Slack to deploy the changes to WordPress.com simple once the build is done.

If you have questions about anything, reach out in #jetpack-developers for guidance!

[jp-launch-control]

Code Coverage Summary

This PR did not change code coverage!

That could be good or bad, depending on the situation. Everything covered before, and still is? Great! Nothing was covered before? Not so great. 🤷

Full summary · PHP report · JS report