WP_Theme cannot locate a parent block theme

[dd32]

As reported here: ​https://github.com/WordPress/gutenberg/issues/45811 after a discussion in slack: ​https://wordpress.slack.com/archives/C02QB8GMM/p1668569269811889

On wp-themes.com we're running into a use-case where the Parent theme cannot be located when both the parent and child theme are block themes, and the parent does not have an index.php file.

(See screenshot attached below, where the parent theme is 100% most definitely installed)

This appears to work on some installations, but not on others. I believe it working might be down to caching, I haven't figured that out.

The attached PR updates the code in WP_Theme to support the same theme files as supported via [53416] for themes in parent themes.

Trac ticket: https://core.trac.wordpress.org/ticket/57141

[dd32]

I'm not familiar enough with the rest of this code to really figure out if the PR is a complete solution, but it appears to work for me.

[dd32]

Note: While ​https://github.com/WordPress/gutenberg/issues/45811 suggests that Gutenberg needs to be active to trigger the issue, I can duplicate the WP_Theme issues with or without it.