Navigation Submenu: Parent dropdown arrow and submenu container visible on viewports where all children are hidden #78147

Description

This was originally reported on WordPress Core Trac ticket here: https://core.trac.wordpress.org/ticket/64835

When all child items of a core/navigation-submenu block are hidden on a specific viewport block, the parent item still renders its dropdown arrow and submenu container on that viewport.

On further check, it looks like items hidden via "Hide on Desktop/Tablet/Mobile" still emit their full HTML and the hiding is handled purely by CSS via wp-block-hidden-* classes on the child <li>. So $inner_blocks_html is never empty, and $has_submenu is always true regardless of visibility settings.

Step-by-step reproduction instructions

1. Create a page with a Navigation block
2. Add a submenu parent item
3. Add one or more child links inside it
4. For each child, click on three dots for block settings > Hide > select all viewport options.
5. Save and preview on the front end

Expected: The parent item renders as a plain link with no dropdown arrow and no submenu container, since there are no visible children on
any viewport.

Actual: The parent item still shows a dropdown arrow and renders an empty submenu container

Screenshots, screen recording, code snippet

Environment info

• WordPress: 7.1-alpha-62201
• PHP: 8.3.30
• Server: Apache/2.4.66 (Debian)
• Database: mysqli (Server: 11.8.6-MariaDB-ubu2404 / Client: mysqlnd 8.3.30)
• Browser: Chrome 146.0.0.0
• OS: macOS
• Theme: Twenty Twenty-Five 1.4
• MU Plugins: None activated
• Plugins:
  • Gutenberg 23.1.0-rc.1
  • Test Reports 1.2.1

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

Please confirm which theme type you used for testing.

• Block
• Classic
• Hybrid (e.g. classic with theme.json)
• Not sure