Template Part Block: Load content from the parent theme if there no template in a child theme

[scruffian]

Description

If a child theme wants to modify a template from a parent theme, it will then need to redefine the header and footer template parts. With this change the theme will fall back to the parent theme template unless the child theme defines it. With this change child themes will be able to be much simpler.

How has this been tested?

With Skatepark: https://github.com/Automattic/themes/tree/7e8706ed7f703aacbbe00b9a1b182b2f2cede76e/skatepark

With this change, Skatepark won't need to redefine header and footer template parts, it will inherit the ones in Blockbase.

Types of changes

New feature (non-breaking change which adds functionality)

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• I've tested my changes with keyboard and screen readers.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR (please manually search all *.native.js files for terms that need renaming or removal).

[Mamaduka]

Hi, @scruffian

I created PR to bring essential child theme support for FSE - #34354. PR also takes a slightly different approach to handle this case.

Your feedback would be much appriciated.

Thanks

[carolinan]

This PR is working well for me.

• The child theme displays the parent theme template parts in the editors and front.
• The parent theme template part can be overwritten by adding a new template part in the child theme.

[carolinan]

#34354 also works well so it depends on which is the preferred approach.

[Mamaduka]

#34354 got merged, which should handle template overrides.