Block editor: Can not edit slug with "Show template" enabled

[carolinan]

Description

When editing a page or post in the block editor, and "Show template" is enabled,
I can not edit the slug correctly due to a bug.

A soon as I enter a character into the slug input field in the popover, the change is saved and the page "refreshes":
The page content becomes blank for a moment until the blocks shows again, and the popover is closed.
So, I can only enter one character at the time.

This happens with Gutenberg trunk enabled.
In 6.8 beta, without Gutenberg active, the canvas blinks and refreshes when I enter each character into the slug field. But the popover does not close, so I can continue entering my updated slug into the field.

Step-by-step reproduction instructions

Activate a block theme.
Create or edit a page or post in the block editor.

Enable "show template".
Open the document panel.
Open the slug popover by clicking on the link next to the text "Slug"
Try entering a long slug.

Screenshots, screen recording, code snippet

With Gutenberg active:

page-slug.mp4

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

Please confirm which theme type you used for testing.

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

[carolinan]

If I assign a different template than the default "page" template, this bug does not happen, entering the slug works:

Activate Twenty Twenty-Five
Create a new page.
Add a title.
In the template section in the document panel, assign the page template "page no title".
Save.
Try editing the slug.

In the template section in the document panel, select "create new template".
Save.
Try editing the slug.

[carolinan]

If zoom out is enabled when you try to edit the slug, the zoom out is disabled when you start typing, but the option in the toolbar still shows it as enabled.

[Mamaduka]

Thanks for testing this feature, @carolinan!

In 6.8 beta, without Gutenberg active, the canvas blinks and refreshes when I enter each character into the slug field. But the popover does not close, so I can continue entering my updated slug into the field.

I'm getting the same behavior here. We've not shipped anything for this logic since Beta 1.

The problem comes from this part of the selector since changing the post type slug also affects potential template ID resolution.

gutenberg/packages/core-data/src/private-selectors.ts

Lines 242 to 258 in 66394c4

	// If no template is assigned, use the default template.
	let slugToCheck;
	// In `draft` status we might not have a slug available, so we use the `single`
	// post type templates slug(ex page, single-post, single-product etc..).
	// Pages do not need the `single` prefix in the slug to be prioritized
	// through template hierarchy.
	if ( editedEntity.slug ) {
	slugToCheck =
	postType === 'page'
	? `${ postType }-${ editedEntity.slug }`
	: `single-${ postType }-${ editedEntity.slug }`;
	} else {
	slugToCheck = postType === 'page' ? 'page' : `single-${ postType }`;
	}
	return select( STORE_NAME ).getDefaultTemplateId( {
	slug: slugToCheck,
	} );

[Mamaduka]

Started a draft PR - #69516.