Table of Contents: prevent headings of template from rendering in list in Site Editor

[ntsekouras]

Description

If we have page that contains a Table of Contents block and we view this page in the site editor, the block also renders the other template headers. I'm not sure if this is something known and if is something wrong with how the headings are assigned to that block.

This might be serious enough because of the side effects of the block to update its attributes based on existing static markup and the discovery method it uses to find headings. In such a case if we render the template in a BlockPreview, it crashes the browser. It was discovered here. It seems that by using getClientIdsWithDescendants when we are in site editor has unexpected results.

Step-by-step reproduction instructions

1. In a page add a heading and a TOC block.
2. View that page in site editor
3. Edit the template and add some more headers
4. View the page again
5. Observe that the TOC inside the Post Content block also renders the template's headings.

Screenshots, screen recording, code snippet

Screen.Recording.2023-09-12.at.5.19.49.PM.mov

Environment info

No response

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

[alexstine]

FYI @Mamaduka is currently working on some enhancements for the block. Not sure if this is included or not.

[Mamaduka]

Yes, this is on my list.

[annezazu]

Came here to report this too after I found it showed the Comments block heading:

table.of.contents.bug.mov

[Mamaduka]

@ntsekouras, can you provide steps on how I can reproduce the error described here - #51477 (comment).

[ntsekouras]

@ntsekouras, can you provide steps on how I can reproduce the error described here - #51477 (comment).

• In a page add a heading and a TOC block.
• View that page in site editor
• Edit the template to add an extra heading block
• In template inspector sidebar click on the template name and select swap template.

[Mamaduka]

I just tested the above scenario with #54224. There's no error, and the editor doesn't crash when viewing template-swapping options.

I can still see extra headings from the templates.

[ntsekouras]

Hope the video helps to reproduce.

Screen.Recording.2023-09-13.at.2.02.02.PM.mov

[Mamaduka]

@ntsekouras, I meant that I can reproduce the error on trunk but not when testing with recent changes to Toc block #54224.

[mrfoxtalbot]

I can still reproduce this. If I add the TOC to the single post template....

... it lists the headings footer's template, not in the post content:

That said, fixing #41173 will also fix this issue so I will close this one.