Users Can Wrongly Set a Custom Page Template when front-page.php is in Use

[davidakennedy]

If you try to set a custom page template in a theme that uses a front-page.php, front-page.php always wins. This is expected, but a user doesn't know that. They're still able to save the page, and it looks like it should work, but on the front end, front-page.php wins, and they may be left confused.

Discovered while researching #39299.

Steps to reproduce:

1. Activate Twenty Seventeen.
2. Set the front page to a static page.
3. Create a page template.
4. Assign it to the static page being used as the front page.
5. Save.
6. Visit front end – the template isn't used.

What I expected?

At the very least – WordPress doesn't save this change, and provides an error message. Better: The page template selection box doesn't show up in this case because setting a template when the front page is a static page and a theme has front-page.php isn't possible.

[davidakennedy]

Shows static page with template in use in theme with front-page.php

[swissspidy]

The page template selection box doesn't show up in this case because setting a template when the front page is a static page and a theme has front-page.php isn't possible.

What if the page template was previously set, i.e. before the page was chosen as the static front page.

While we're at it: what about the posts page?

[johnbillion]

Replying to swissspidy:

While we're at it: what about the posts page?

It's not possible to set a page template for the posts page.