Template part areas display as "undefined" in the template editor

[carolinan]

Description

When you add a template part in the template editor, (either template part, header, or footer aliases) and select "Choose existing",
the area displays as "Undefined".

Step-by-step reproduction instructions

1. Activate a theme with support for template editing, for example Twenty Twenty-Two
2. Open a template in the template editor
3. Add a template part. Select "Choose existing"
4. See that the area is undefined.

Screenshots, screen recording, code snippet

Environment info

WordPress 5.9.0 beta 3 via the beta tester
With and without Gutenberg trunk.

Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

No

[Mamaduka]

I think we forgot to backport this part of the editor settings into the WP core. I'm not able to reproduce this with the Gutenberg trunk.

gutenberg/lib/editor-settings.php

Lines 27 to 29 in b383713

	if ( wp_is_block_theme() ) {
	$settings['defaultTemplatePartAreas'] = get_allowed_block_template_part_areas();
	}

[carolinan]

Would that be in get_default_block_editor_settings()? https://github.com/WordPress/wordpress-develop/blob/trunk/src/wp-includes/block-editor.php#L154

Or get_block_editor_settings() https://github.com/WordPress/wordpress-develop/blob/trunk/src/wp-includes/block-editor.php#L300

[tellthemachines]

I can't reproduce this locally with WP trunk plus the package updates for Beta 4.

[hellofromtonya]

WordPress Core's changeset 52232 added the defaultTemplatePartAreas setting:

$block_editor_context = new WP_Block_Editor_Context();
$custom_settings      = array(
	'siteUrl'                              => site_url(),
	'postsPerPage'                         => get_option( 'posts_per_page' ),
	'styles'                               => get_block_editor_theme_styles(),
	'defaultTemplateTypes'                 => $indexed_template_types,
	'defaultTemplatePartAreas'             => get_allowed_block_template_part_areas(),
	'__experimentalBlockPatterns'          => WP_Block_Patterns_Registry::get_instance()->get_all_registered(),
	'__experimentalBlockPatternCategories' => WP_Block_Pattern_Categories_Registry::get_instance()->get_all_registered(),
);
$editor_settings      = get_block_editor_settings( $custom_settings, $block_editor_context );

I'm not seeing other changes to that setting in Core since that commit.

And get_allowed_block_template_part_areas() was committed 6 weeks ago with changeset 52062.

[hellofromtonya]

Removing the backport label until the needed backport is identified.

[carolinan]

Changeset 52232 changes wp-admin/site-editor.php, is that used for the template editor? Which is part of the block editor, not the site editor.

[carolinan]

I can't reproduce this locally with WP trunk plus the package updates for Beta 4.

How did you add the template part? I am still unable to add a template part block using 5.9-beta4-52408-src.

[Mamaduka]

I was able to reproduce this with beta 4. It should be fixed via a core patch, and I will create it shortly.

[Mamaduka]

Core PR: WordPress/wordpress-develop#2076

[Mamaduka]

The core patch got merged - https://core.trac.wordpress.org/changeset/52409.

I am closing the issue since there's no change required on the plugin side.