Use template editing mode when editing a template via Appearance > Templates

[jameskoster]

Currently, if you navigate to Appearance > Templates and open a template, the post editor mode is used. IE the content area is squished into a narrow column, and the document title is visible on the canvas.

This should instead use the same mode as when you edit a template in the site editor, or via the "Template" section of the Inspector when editing a post.

[carolinan]

Agreed, that it is using the post editor mode is something that has been confusing to both users and developers when I have tried to explain how templates work.

[carolinan]

So where would the edit link lead to if the template is not assigned to a post/page/custom post type?
What if it is assigned to more than one post? Then you'd have to select which post to open with the template editing mode.

Especially if the site editor is not in 5.9. If it is in 5.9, I think the edit link would need to go there.

[carolinan]

The site editor uses a URL format with the theme name and the name (slug) of the template.
admin.php?page=gutenberg-edit-site&postId=theme-experiments%2Femptytheme%2F%2Fsingular&postType=wp_template

The edit link in the appearance > templates view would need to be updated to point to the site editor.
I was not able to figure out how to update/filter the _edit_link argument of register_post_type to include the theme name and template name, so perhaps the site editor could be updated to accept the post id instead.

[jameskoster]

So where would the edit link lead to if the template is not assigned to a post/page/custom post type?
What if it is assigned to more than one post? Then you'd have to select which post to open with the template editing mode.

This is a template editing environment, so my expectation would be that they all link to a view where you edit the template, not the content. Something like:

In the future it might be nice to preview different items of compatible content while editing the template, but that doesn't seem essential for now.

[carlomanf]

Please look at addressing #36060 as a follow-up to this, because the post editor mode did enable access to revisions and the new mode should enable similar access.