Child theme should appear as broken if parent is itself

[davilera]

Child themes are defined as such if they include the Template header in style.css. In general, if the parent template can't be found, WordPress reports the theme as Broken and tells the user to install the missing parent theme.

However, if the Template header is the theme itself, no errors are reported (WordPress can find the "parent" theme, because it's itself). The resulting behavior is weird and unexpected:

• If there are other themes available, WordPress uses one as the parent theme (I don't know which criteria is used for selecting one or the other).
• If there aren't, the front-end is completely blank (but this might depend on the amount of code included in the child theme).

Such an (invalid) child theme should be reported as Broken. For instance, the following message could be shown: The theme defines itself as its parent theme. Please fix the "Template" header.

[davilera]

Adds an extra check to make sure that the parent theme of a child theme is not the child theme itself.

[davilera]

I just uploaded a new patch 40820.diff​ along with a Unit Test.

[swissspidy]

40820.2.diff​ is an updated patch that adjusts other theme unit tests because of that new test theme.

[swissspidy]

In 41601:

Themes: Report theme as broken that sets itself as its parent.

Props davilera.
Fixes #40820.

[obenland]

@swissspidy What do you think about setting Template in <code> tags?

[swissspidy]

In 41607:

Themes: Adjust translated string after [41601].

Props obenland.
See #40820.

[swissspidy]

In 41610:

Themes: Adjust unit test after [41607].

Props ocean90.
See #40820.