The Library page in Hybrid Themes that support Template Parts has a broken homepage preview

[aurooba]

Description

This is a similar issue to what we saw in the 6.2 beta, #48391, and it's reproducible again in 6.2.2 – I'm not sure if it came back in 6.2.1, but it was fixed and confirmed fixed when the initial 6.2 release happened. I just noticed it again.

Step-by-step reproduction instructions

1. Activate a classic theme with theme.json and support for block template parts that includes at least one block template part. (happy to provide an example theme if needed)
2. Go to Appearance > Template Parts
3. Click on the back button for All Template Parts
4. See the loading screen where the homepage should be – this page shouldn't exist for hybrid themes, from my understanding, it should go straight back to the dashboard.

Screenshots, screen recording, code snippet

Without Gutenberg

Screen.Recording.2023-06-07.at.6.56.00.AM.mov

With Gutenberg 15.9.1

Screen.Recording.2023-06-07.at.7.08.18.AM.mov

Environment info

• WordPress 6.2.2
• Tested with AND without Gutenberg 15.9.1

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

[annezazu]

@Mamaduka in case you might be able to dig in!

[t-hamano]

WordPress 6.3 and the latest Gutenberg behave differently: when you press the back button on the All Template Parts page, it takes you to the Library page, but the loading status is not displayed in the canvas area, but the registered pattern is displayed.

I would like to close this issue as I believe this problem is no longer reproduced.

However, I have submitted issue #52150 because I don't believe it is strictly intended that non-block themes that support block template parts be able to access the Library page.