Post editor: Template panel should adapt when explicit template exists

[jameskoster]

Follow up to #41189.

When a template exists that automatically resolves to display a specific post or page (e.g. single-post-$slug), the Template panel in the post editor will need some adjustments when editing the corresponding post:

• It should not be possible to create a new template – this is misleading as it suggests the new template could be applied to the current post.
• The template dropdown should be hidden since it isn't possible to change the template.
• Some text explaining the above could eliminate potential confusion.
• We might consider adding a way to delete the explicit template.

If we added a delete action it should invoke a confirmation modal that explains which template will be used after deletion.

Edit: To clarify, the explicit template is only applied automatically if a $custom template has not been applied previously. So the UI above should only be presented when no $custom templates exist at all.

[jameskoster]

This pretty much feels like a bug at the moment.

After creating a template for a specific post I can actually change which template is applied when editing that post, which undermines the specific template logic altogether.

[carolinan]

I tried to solve this in components> sidebar > post-template but I got stuck because the template slug is not defined for the "Default" template:
I am not sure how to differentiate single.html from single-post-$slug.html, because they would both have no template slug value and both would be valid defaults? The options should only change if single-post-$slug.html is available.

[jameskoster]

@noisysocks has been working with the template panel recently, perhaps it's something he can look into? 🙏

[noisysocks]

What happens if the post already has a template that was created using the post editor sidebar?

[jameskoster]

That is a very good question, and I am once again humbled by the template hierarchy 🙈

Currently templates created in the post editor are $custom and therefore above specific templates (such as single-post-hello-world) in the hierarchy. I mistakenly thought it was the other way around.

So actually the current behavior of the template panel is correct – I am able to select a $custom template, or the template that was created for that specific post.

The flow of creating a template for a specific post and not applying it feels a bit strange, but that's something to explore separately. I'll close this issue.

[noisysocks]

It's definitely confusing 😅 I don't really like that we have two flows to accomplish what amounts to the same thing.

[jameskoster]

Turns out the explicit template is applied automatically, but only when a custom template hasn't been applied. Re-opening and updating the OP :D