Can't change the slug of a wp_template

[aristath]

Description

Trying to create a template for a page with id=2 in an FSE theme I found it impossible to set the slug of the template to page-2so it only gets applied to a specific page.

Step-by-step reproduction instructions

1. From the dashboard go to Appearance > Templates
2. Create a new template. Add a title and save it. The slug is saved as custom_slug_602145e030737, containing a unique ID instead of the title slug-ified.
3. Refresh the page, and from the sidebar change the slug to page-2
4. After refreshing the page you will see the slug wasn't changed, and as a result the template does not get applied to the corresponding page.

If I go in the database and manually change the slug of the post there, the template gets properly applied to the page on the frontend.

Expected behaviour

• On initial save, the slug should be built from the title instead of getting a slug custom_slug_*.
• If the user changes the slug from the slug field, the changes should be saved.

WordPress information

• WordPress version: 5.7-beta1
• Gutenberg version: 9.9.1
• Are all plugins except Gutenberg deactivated? Yes

[mtias]

@aristath are you still experiencing this issue?

[aristath]

This is no longer replicable.
We have removed the "Templates" menu under Appearance, and when trying to create a new template from the site-editor, we now have a limited selection of templates that can be created.
So it's still not possible to create a template for a specific page (a page-2.html template) from the site-editor, but for different reasons.
I'll go ahead and close this one since it's no longer relevant, a lot of things have changed since this issue was created 👍