Editor: Add block theme infrastructure

Adds the required infrastructure to render block-based themes. This is sourced
from the Gutenberg plugin.

Fixes #54335.
Props bernhard-reiter, youknowriad, ntsekouras, hellofromtonya.

Built from https://develop.svn.wordpress.org/trunk@52062


git-svn-id: http://core.svn.wordpress.org/trunk@51654 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/block-template-utils.php

@@ -1,23 +1,495 @@
 <?php
 /**
- * Utilities used to fetch and create templates.
+ * Utilities used to fetch and create templates and template parts.
  *
  * @package WordPress
  * @since 5.8.0
  */
 
+// Define constants for supported wp_template_part_area taxonomy.
+if ( ! defined( 'WP_TEMPLATE_PART_AREA_HEADER' ) ) {
+	define( 'WP_TEMPLATE_PART_AREA_HEADER', 'header' );
+}
+if ( ! defined( 'WP_TEMPLATE_PART_AREA_FOOTER' ) ) {
+	define( 'WP_TEMPLATE_PART_AREA_FOOTER', 'footer' );
+}
+if ( ! defined( 'WP_TEMPLATE_PART_AREA_SIDEBAR' ) ) {
+	define( 'WP_TEMPLATE_PART_AREA_SIDEBAR', 'sidebar' );
+}
+if ( ! defined( 'WP_TEMPLATE_PART_AREA_UNCATEGORIZED' ) ) {
+	define( 'WP_TEMPLATE_PART_AREA_UNCATEGORIZED', 'uncategorized' );
+}
+
+/**
+ * Returns a filtered list of allowed area values for template parts.
+ *
+ * @since 5.9.0
+ *
+ * @return array The supported template part area values.
+ */
+function get_allowed_block_template_part_areas() {
+	$default_area_definitions = array(
+		array(
+			'area'        => WP_TEMPLATE_PART_AREA_UNCATEGORIZED,
+			'label'       => __( 'General' ),
+			'description' => __(
+				'General templates often perform a specific role like displaying post content, and are not tied to any particular area.'
+			),
+			'icon'        => 'layout',
+			'area_tag'    => 'div',
+		),
+		array(
+			'area'        => WP_TEMPLATE_PART_AREA_HEADER,
+			'label'       => __( 'Header' ),
+			'description' => __(
+				'The Header template defines a page area that typically contains a title, logo, and main navigation.'
+			),
+			'icon'        => 'header',
+			'area_tag'    => 'header',
+		),
+		array(
+			'area'        => WP_TEMPLATE_PART_AREA_FOOTER,
+			'label'       => __( 'Footer' ),
+			'description' => __(
+				'The Footer template defines a page area that typically contains site credits, social links, or any other combination of blocks.'
+			),
+			'icon'        => 'footer',
+			'area_tag'    => 'footer',
+		),
+	);
+
+	/**
+	 * Filters the list of allowed template part area values.
+	 *
+	 * @since 5.9.0
+	 *
+	 * @param array $default_areas An array of supported area objects.
+	 */
+	return apply_filters( 'default_wp_template_part_areas', $default_area_definitions );
+}
+
+
+/**
+ * Returns a filtered list of default template types, containing their
+ * localized titles and descriptions.
+ *
+ * @since 5.9.0
+ *
+ * @return array The default template types.
+ */
+function get_default_block_template_types() {
+	$default_template_types = array(
+		'index'          => array(
+			'title'       => _x( 'Index', 'Template name' ),
+			'description' => __( 'The default template used when no other template is available. This is a required template in WordPress.' ),
+		),
+		'home'           => array(
+			'title'       => _x( 'Home', 'Template name' ),
+			'description' => __( 'Template used for the main page that displays blog posts. This is the front page by default in WordPress. If a static front page is set, this is the template used for the page that contains the latest blog posts.' ),
+		),
+		'front-page'     => array(
+			'title'       => _x( 'Front Page', 'Template name' ),
+			'description' => __( 'Template used to render the front page of the site, whether it displays blog posts or a static page. The front page template takes precedence over the "Home" template.' ),
+		),
+		'singular'       => array(
+			'title'       => _x( 'Singular', 'Template name' ),
+			'description' => __( 'Template used for displaying single views of the content. This template is a fallback for the Single, Post, and Page templates, which take precedence when they exist.' ),
+		),
+		'single'         => array(
+			'title'       => _x( 'Single Post', 'Template name' ),
+			'description' => __( 'Template used to display a single blog post.' ),
+		),
+		'page'           => array(
+			'title'       => _x( 'Page', 'Template name' ),
+			'description' => __( 'Template used to display individual pages.' ),
+		),
+		'archive'        => array(
+			'title'       => _x( 'Archive', 'Template name' ),
+			'description' => __( 'The archive template displays multiple entries at once. It is used as a fallback for the Category, Author, and Date templates, which take precedence when they are available.' ),
+		),
+		'author'         => array(
+			'title'       => _x( 'Author', 'Template name' ),
+			'description' => __( 'Archive template used to display a list of posts from a single author.' ),
+		),
+		'category'       => array(
+			'title'       => _x( 'Category', 'Template name' ),
+			'description' => __( 'Archive template used to display a list of posts from the same category.' ),
+		),
+		'taxonomy'       => array(
+			'title'       => _x( 'Taxonomy', 'Template name' ),
+			'description' => __( 'Archive template used to display a list of posts from the same taxonomy.' ),
+		),
+		'date'           => array(
+			'title'       => _x( 'Date', 'Template name' ),
+			'description' => __( 'Archive template used to display a list of posts from a specific date.' ),
+		),
+		'tag'            => array(
+			'title'       => _x( 'Tag', 'Template name' ),
+			'description' => __( 'Archive template used to display a list of posts with a given tag.' ),
+		),
+		'attachment'     => array(
+			'title'       => __( 'Media' ),
+			'description' => __( 'Template used to display individual media items or attachments.' ),
+		),
+		'search'         => array(
+			'title'       => _x( 'Search', 'Template name' ),
+			'description' => __( 'Template used to display search results.' ),
+		),
+		'privacy-policy' => array(
+			'title'       => __( 'Privacy Policy' ),
+			'description' => '',
+		),
+		'404'            => array(
+			'title'       => _x( '404', 'Template name' ),
+			'description' => __( 'Template shown when no content is found.' ),
+		),
+	);
+
+	/**
+	 * Filters the list of template types.
+	 *
+	 * @since 5.9.0
+	 *
+	 * @param array $default_template_types An array of template types, formatted as [ slug => [ title, description ] ].
+	 */
+	return apply_filters( 'default_template_types', $default_template_types );
+}
+
+/**
+ * Checks whether the input 'area' is a supported value.
+ * Returns the input if supported, otherwise returns the 'uncategorized' value.
+ *
+ * @access private
+ * @since 5.9.0
+ *
+ * @param string $type Template part area name.
+ *
+ * @return string Input if supported, else the uncategorized value.
+ */
+function _filter_block_template_part_area( $type ) {
+	$allowed_areas = array_map(
+		static function ( $item ) {
+			return $item['area'];
+		},
+		get_allowed_block_template_part_areas()
+	);
+	if ( in_array( $type, $allowed_areas, true ) ) {
+		return $type;
+	}
+
+	$warning_message = sprintf(
+		/* translators: %1$s: Template area type, %2$s: the uncategorized template area value. */
+		__( '"%1$s" is not a supported wp_template_part area value and has been added as "%2$s".' ),
+		$type,
+		WP_TEMPLATE_PART_AREA_UNCATEGORIZED
+	);
+	trigger_error( $warning_message, E_USER_NOTICE );
+	return WP_TEMPLATE_PART_AREA_UNCATEGORIZED;
+}
+
+/**
+ * Finds all nested template part file paths in a theme's directory.
+ *
+ * @access private
+ * @since 5.9.0
+ *
+ * @param string $base_directory The theme's file path.
+ * @return array $path_list A list of paths to all template part files.
+ */
+function _get_block_templates_paths( $base_directory ) {
+	$path_list = array();
+	if ( file_exists( $base_directory ) ) {
+		$nested_files      = new RecursiveIteratorIterator( new RecursiveDirectoryIterator( $base_directory ) );
+		$nested_html_files = new RegexIterator( $nested_files, '/^.+\.html$/i', RecursiveRegexIterator::GET_MATCH );
+		foreach ( $nested_html_files as $path => $file ) {
+			$path_list[] = $path;
+		}
+	}
+	return $path_list;
+}
+
+/**
+ * Retrieves the template file from the theme for a given slug.
+ *
+ * @access private
+ * @since 5.9.0
+ *
+ * @param string $template_type wp_template or wp_template_part.
+ * @param string $slug template slug.
+ *
+ * @return array|null Template.
+ */
+function _get_block_template_file( $template_type, $slug ) {
+	if ( 'wp_template' !== $template_type && 'wp_template_part' !== $template_type ) {
+		return null;
+	}
+
+	$template_base_paths = array(
+		'wp_template'      => 'block-templates',
+		'wp_template_part' => 'block-template-parts',
+	);
+	$themes              = array(
+		get_stylesheet() => get_stylesheet_directory(),
+		get_template()   => get_template_directory(),
+	);
+	foreach ( $themes as $theme_slug => $theme_dir ) {
+		$file_path = $theme_dir . '/' . $template_base_paths[ $template_type ] . '/' . $slug . '.html';
+		if ( file_exists( $file_path ) ) {
+			$new_template_item = array(
+				'slug'  => $slug,
+				'path'  => $file_path,
+				'theme' => $theme_slug,
+				'type'  => $template_type,
+			);
+
+			if ( 'wp_template_part' === $template_type ) {
+				return _add_block_template_part_area_info( $new_template_item );
+			}
+
+			if ( 'wp_template' === $template_type ) {
+				return _add_block_template_info( $new_template_item );
+			}
+
+			return $new_template_item;
+		}
+	}
+
+	return null;
+}
+
+/**
+ * Retrieves the template files from  the theme.
+ *
+ * @access private
+ * @since 5.9.0
+ *
+ * @param string $template_type wp_template or wp_template_part.
+ *
+ * @return array Template.
+ */
+function _get_block_templates_files( $template_type ) {
+	if ( 'wp_template' !== $template_type && 'wp_template_part' !== $template_type ) {
+		return null;
+	}
+
+	$template_base_paths = array(
+		'wp_template'      => 'block-templates',
+		'wp_template_part' => 'block-template-parts',
+	);
+	$themes              = array(
+		get_stylesheet() => get_stylesheet_directory(),
+		get_template()   => get_template_directory(),
+	);
+
+	$template_files = array();
+	foreach ( $themes as $theme_slug => $theme_dir ) {
+		$theme_template_files = _get_block_templates_paths( $theme_dir . '/' . $template_base_paths[ $template_type ] );
+		foreach ( $theme_template_files as $template_file ) {
+			$template_base_path = $template_base_paths[ $template_type ];
+			$template_slug      = substr(
+				$template_file,
+				// Starting position of slug.
+				strpos( $template_file, $template_base_path . DIRECTORY_SEPARATOR ) + 1 + strlen( $template_base_path ),
+				// Subtract ending '.html'.
+				-5
+			);
+			$new_template_item = array(
+				'slug'  => $template_slug,
+				'path'  => $template_file,
+				'theme' => $theme_slug,
+				'type'  => $template_type,
+			);
+
+			if ( 'wp_template_part' === $template_type ) {
+				$template_files[] = _add_block_template_part_area_info( $new_template_item );
+			}
+
+			if ( 'wp_template' === $template_type ) {
+				$template_files[] = _add_block_template_info( $new_template_item );
+			}
+		}
+	}
+
+	return $template_files;
+}
+
+/**
+ * Attempts to add custom template information to the template item.
+ *
+ * @access private
+ * @since 5.9.0
+ *
+ * @param array $template_item Template to add information to (requires 'slug' field).
+ * @return array Template
+ */
+function _add_block_template_info( $template_item ) {
+	if ( ! WP_Theme_JSON_Resolver::theme_has_support() ) {
+		return $template_item;
+	}
+
+	$theme_data = WP_Theme_JSON_Resolver::get_theme_data()->get_custom_templates();
+	if ( isset( $theme_data[ $template_item['slug'] ] ) ) {
+		$template_item['title']     = $theme_data[ $template_item['slug'] ]['title'];
+		$template_item['postTypes'] = $theme_data[ $template_item['slug'] ]['postTypes'];
+	}
+
+	return $template_item;
+}
+
+/**
+ * Attempts to add the template part's area information to the input template.
+ *
+ * @access private
+ * @since 5.9.0
+ *
+ * @param array $template_info Template to add information to (requires 'type' and 'slug' fields).
+ *
+ * @return array Template.
+ */
+function _add_block_template_part_area_info( $template_info ) {
+	if ( WP_Theme_JSON_Resolver::theme_has_support() ) {
+		$theme_data = WP_Theme_JSON_Resolver::get_theme_data()->get_template_parts();
+	}
+
+	if ( isset( $theme_data[ $template_info['slug'] ]['area'] ) ) {
+		$template_info['title'] = $theme_data[ $template_info['slug'] ]['title'];
+		$template_info['area']  = _filter_block_template_part_area( $theme_data[ $template_info['slug'] ]['area'] );
+	} else {
+		$template_info['area'] = WP_TEMPLATE_PART_AREA_UNCATEGORIZED;
+	}
+
+	return $template_info;
+}
+
+/**
+ * Returns an array containing the references of
+ * the passed blocks and their inner blocks.
+ *
+ * @access private
+ * @since 5.9.0
+ *
+ * @param array $blocks array of blocks.
+ *
+ * @return array block references to the passed blocks and their inner blocks.
+ */
+function _flatten_blocks( &$blocks ) {
+	$all_blocks = array();
+	$queue      = array();
+	foreach ( $blocks as &$block ) {
+		$queue[] = &$block;
+	}
+
+	while ( count( $queue ) > 0 ) {
+		$block = &$queue[0];
+		array_shift( $queue );
+		$all_blocks[] = &$block;
+
+		if ( ! empty( $block['innerBlocks'] ) ) {
+			foreach ( $block['innerBlocks'] as &$inner_block ) {
+				$queue[] = &$inner_block;
+			}
+		}
+	}
+
+	return $all_blocks;
+}
+
+/**
+ * Parses wp_template content and injects the current theme's
+ * stylesheet as a theme attribute into each wp_template_part
+ *
+ * @access private
+ * @since 5.9.0
+ *
+ * @param string $template_content serialized wp_template content.
+ *
+ * @return string Updated wp_template content.
+ */
+function _inject_theme_attribute_in_block_template_content( $template_content ) {
+	$has_updated_content = false;
+	$new_content         = '';
+	$template_blocks     = parse_blocks( $template_content );
+
+	$blocks = _flatten_blocks( $template_blocks );
+	foreach ( $blocks as &$block ) {
+		if (
+			'core/template-part' === $block['blockName'] &&
+			! isset( $block['attrs']['theme'] )
+		) {
+			$block['attrs']['theme'] = wp_get_theme()->get_stylesheet();
+			$has_updated_content     = true;
+		}
+	}
+
+	if ( $has_updated_content ) {
+		foreach ( $template_blocks as &$block ) {
+			$new_content .= serialize_block( $block );
+		}
+
+		return $new_content;
+	}
+
+	return $template_content;
+}
+
+/**
+ * Build a unified template object based on a theme file.
+ *
+ * @access private
+ * @since 5.9.0
+ *
+ * @param array $template_file Theme file.
+ * @param array $template_type wp_template or wp_template_part.
+ *
+ * @return WP_Block_Template Template.
+ */
+function _build_block_template_result_from_file( $template_file, $template_type ) {
+	$default_template_types = get_default_block_template_types();
+	$template_content       = file_get_contents( $template_file['path'] );
+	$theme                  = wp_get_theme()->get_stylesheet();
+
+	$template                 = new WP_Block_Template();
+	$template->id             = $theme . '//' . $template_file['slug'];
+	$template->theme          = $theme;
+	$template->content        = _inject_theme_attribute_in_block_template_content( $template_content );
+	$template->slug           = $template_file['slug'];
+	$template->source         = 'theme';
+	$template->type           = $template_type;
+	$template->title          = ! empty( $template_file['title'] ) ? $template_file['title'] : $template_file['slug'];
+	$template->status         = 'publish';
+	$template->has_theme_file = true;
+	$template->is_custom      = true;
+
+	if ( 'wp_template' === $template_type && isset( $default_template_types[ $template_file['slug'] ] ) ) {
+		$template->description = $default_template_types[ $template_file['slug'] ]['description'];
+		$template->title       = $default_template_types[ $template_file['slug'] ]['title'];
+		$template->is_custom   = false;
+	}
+
+	if ( 'wp_template' === $template_type && isset( $template_file['postTypes'] ) ) {
+		$template->post_types = $template_file['postTypes'];
+	}
+
+	if ( 'wp_template_part' === $template_type && isset( $template_file['area'] ) ) {
+		$template->area = $template_file['area'];
+	}
+
+	return $template;
+}
+
 /**
  * Build a unified template object based a post Object.
  *
  * @access private
- * @since 5.8.0
+ * @since 5.9.0
  *
  * @param WP_Post $post Template post.
  *
  * @return WP_Block_Template|WP_Error Template.
  */
-function _build_template_result_from_post( $post ) {
+function _build_block_template_result_from_post( $post ) {
-	$terms = get_the_terms( $post, 'wp_theme' );
+	$default_template_types = get_default_block_template_types();
+	$terms                  = get_the_terms( $post, 'wp_theme' );
 
 	if ( is_wp_error( $terms ) ) {
 		return $terms;
@@ -27,7 +499,9 @@ function _build_template_result_from_post( $post ) {
 		return new WP_Error( 'template_missing_theme', __( 'No theme is defined for this template.' ) );
 	}
 
-	$theme = $terms[0]->name;
+	$theme          = $terms[0]->name;
+	$has_theme_file = wp_get_theme()->get_stylesheet() === $theme &&
+		null !== _get_block_template_file( $post->post_type, $post->post_name );
 
 	$template                 = new WP_Block_Template();
 	$template->wp_id          = $post->ID;
@@ -40,7 +514,19 @@ function _build_template_result_from_post( $post ) {
 	$template->description    = $post->post_excerpt;
 	$template->title          = $post->post_title;
 	$template->status         = $post->post_status;
-	$template->has_theme_file = false;
+	$template->has_theme_file = $has_theme_file;
+	$template->is_custom      = true;
+
+	if ( 'wp_template' === $post->post_type && isset( $default_template_types[ $template->slug ] ) ) {
+		$template->is_custom = false;
+	}
+
+	if ( 'wp_template_part' === $post->post_type ) {
+		$type_terms = get_the_terms( $post, 'wp_template_part_area' );
+		if ( ! is_wp_error( $type_terms ) && false !== $type_terms ) {
+			$template->area = $type_terms[0]->name;
+		}
+	}
 
 	return $template;
 }
@@ -53,13 +539,40 @@ function _build_template_result_from_post( $post ) {
  * @param array $query {
  *     Optional. Arguments to retrieve templates.
  *
- *     @type array  $slug__in List of slugs to include.
+ *     @type array  $slug__in  List of slugs to include.
- *     @type int    $wp_id Post ID of customized template.
+ *     @type int    $wp_id     Post ID of customized template.
+ *     @type string $area      A 'wp_template_part_area' taxonomy value to filter by (for wp_template_part template type only).
+ *     @type string $post_type Post type to get the templates for.
  * }
- * @param string $template_type Optional. The template type (post type). Default 'wp_template'.
+ * @param array $template_type wp_template or wp_template_part.
- * @return WP_Block_Template[] Block template objects.
+ *
+ * @return array Templates.
  */
 function get_block_templates( $query = array(), $template_type = 'wp_template' ) {
+	/**
+	 * Filters the block templates array before the query takes place.
+	 *
+	 * Return a non-null value to bypass the WordPress queries.
+	 *
+	 * @since 5.9
+	 *
+	 * @param WP_Block_Template[]|null $block_templates Return an array of block templates to short-circuit the default query,
+	 *                                                  or null to allow WP to run it's normal queries.
+	 * @param array $query {
+	 *     Optional. Arguments to retrieve templates.
+	 *
+	 *     @type array  $slug__in List of slugs to include.
+	 *     @type int    $wp_id Post ID of customized template.
+	 *     @type string $post_type Post type to get the templates for.
+	 * }
+	 * @param array $template_type wp_template or wp_template_part.
+	 */
+	$templates = apply_filters( 'pre_get_block_templates', null, $query, $template_type );
+	if ( ! is_null( $templates ) ) {
+		return $templates;
+	}
+
+	$post_type     = isset( $query['post_type'] ) ? $query['post_type'] : '';
 	$wp_query_args = array(
 		'post_status'    => array( 'auto-draft', 'draft', 'publish' ),
 		'post_type'      => $template_type,
@@ -74,11 +587,20 @@ function get_block_templates( $query = array(), $template_type = 'wp_template' )
 		),
 	);
 
+	if ( 'wp_template_part' === $template_type && isset( $query['area'] ) ) {
+		$wp_query_args['tax_query'][]           = array(
+			'taxonomy' => 'wp_template_part_area',
+			'field'    => 'name',
+			'terms'    => $query['area'],
+		);
+		$wp_query_args['tax_query']['relation'] = 'AND';
+	}
+
 	if ( isset( $query['slug__in'] ) ) {
 		$wp_query_args['post_name__in'] = $query['slug__in'];
 	}
 
-	// This is only needed for the regular templates CPT listing and editor.
+	// This is only needed for the regular templates/template parts CPT listing and editor.
 	if ( isset( $query['wp_id'] ) ) {
 		$wp_query_args['p'] = $query['wp_id'];
 	} else {
@@ -88,14 +610,66 @@ function get_block_templates( $query = array(), $template_type = 'wp_template' )
 	$template_query = new WP_Query( $wp_query_args );
 	$query_result   = array();
 	foreach ( $template_query->posts as $post ) {
-		$template = _build_template_result_from_post( $post );
+		$template = _build_block_template_result_from_post( $post );
 
-		if ( ! is_wp_error( $template ) ) {
+		if ( is_wp_error( $template ) ) {
-			$query_result[] = $template;
+			continue;
+		}
+
+		if ( $post_type && ! $template->is_custom ) {
+			continue;
+		}
+
+		$query_result[] = $template;
+	}
+
+	if ( ! isset( $query['wp_id'] ) ) {
+		$template_files = _get_block_templates_files( $template_type );
+		foreach ( $template_files as $template_file ) {
+			$template = _build_block_template_result_from_file( $template_file, $template_type );
+
+			if ( $post_type && ! $template->is_custom ) {
+				continue;
+			}
+
+			if ( $post_type &&
+				isset( $template->post_types ) &&
+				! in_array( $post_type, $template->post_types, true )
+			) {
+				continue;
+			}
+
+			$is_not_custom   = false === array_search(
+				wp_get_theme()->get_stylesheet() . '//' . $template_file['slug'],
+				array_column( $query_result, 'id' ),
+				true
+			);
+			$fits_slug_query =
+				! isset( $query['slug__in'] ) || in_array( $template_file['slug'], $query['slug__in'], true );
+			$fits_area_query =
+				! isset( $query['area'] ) || $template_file['area'] === $query['area'];
+			$should_include  = $is_not_custom && $fits_slug_query && $fits_area_query;
+			if ( $should_include ) {
+				$query_result[] = $template;
+			}
 		}
 	}
 
-	return $query_result;
+	/**
+	 * Filters the array of queried block templates array after they've been fetched.
+	 *
+	 * @since 5.9
+	 *
+	 * @param WP_Block_Template[] $query_result Array of found block templates.
+	 * @param array $query {
+	 *     Optional. Arguments to retrieve templates.
+	 *
+	 *     @type array  $slug__in List of slugs to include.
+	 *     @type int    $wp_id Post ID of customized template.
+	 * }
+	 * @param array $template_type wp_template or wp_template_part.
+	 */
+	return apply_filters( 'get_block_templates', $query_result, $query, $template_type );
 }
 
 /**
@@ -104,10 +678,29 @@ function get_block_templates( $query = array(), $template_type = 'wp_template' )
  * @since 5.8.0
  *
  * @param string $id            Template unique identifier (example: theme_slug//template_slug).
- * @param string $template_type Optional. The template type (post type). Default 'wp_template'.
+ * @param array  $template_type Optional. Template type: `'wp_template'` or '`wp_template_part'`.
+ *                              Default `'wp_template'`.
+ *
  * @return WP_Block_Template|null Template.
  */
 function get_block_template( $id, $template_type = 'wp_template' ) {
+	/**
+	 * Filters the block templates array before the query takes place.
+	 *
+	 * Return a non-null value to bypass the WordPress queries.
+	 *
+	 * @since 5.9.0
+	 *
+	 * @param WP_Block_Template|null $block_template Return block template object to short-circuit the default query,
+	 *                                               or null to allow WP to run its normal queries.
+	 * @param string $id                             Template unique identifier (example: theme_slug//template_slug).
+	 * @param array  $template_type                  Template type: `'wp_template'` or '`wp_template_part'`.
+	 */
+	$block_template = apply_filters( 'pre_get_block_template', null, $id, $template_type );
+	if ( ! is_null( $block_template ) ) {
+		return $block_template;
+	}
+
 	$parts = explode( '//', $id, 2 );
 	if ( count( $parts ) < 2 ) {
 		return null;
@@ -131,12 +724,116 @@ function get_block_template( $id, $template_type = 'wp_template' ) {
 	$posts                = $template_query->posts;
 
 	if ( count( $posts ) > 0 ) {
-		$template = _build_template_result_from_post( $posts[0] );
+		$template = _build_block_template_result_from_post( $posts[0] );
 
 		if ( ! is_wp_error( $template ) ) {
 			return $template;
 		}
 	}
 
-	return null;
+	$block_template = get_block_file_template( $id, $template_type );
+
+	/**
+	 * Filters the array of queried block templates array after they've been fetched.
+	 *
+	 * @since 5.9
+	 *
+	 * @param WP_Block_Template $block_template The found block template.
+	 * @param string            $id             Template unique identifier (example: theme_slug//template_slug).
+	 * @param array             $template_type  Template type: `'wp_template'` or '`wp_template_part'`.
+	 */
+	return apply_filters( 'get_block_template', $block_template, $id, $template_type );
+}
+
+/**
+ * Retrieves a single unified template object using its id.
+ *
+ * @since 5.9.0
+ *
+ * @param string $id            Template unique identifier (example: theme_slug//template_slug).
+ * @param array  $template_type Optional. Template type: `'wp_template'` or '`wp_template_part'`.
+ *                              Default `'wp_template'`.
+ */
+function get_block_file_template( $id, $template_type = 'wp_template' ) {
+	/**
+	 * Filters the block templates array before the query takes place.
+	 *
+	 * Return a non-null value to bypass the WordPress queries.
+	 *
+	 *
+	 * @since 5.9.0
+	 *
+	 * @param WP_Block_Template|null $block_template Return block template object to short-circuit the default query,
+	 *                                               or null to allow WP to run its normal queries.
+	 * @param string $id                             Template unique identifier (example: theme_slug//template_slug).
+	 * @param array  $template_type                  Template type: `'wp_template'` or '`wp_template_part'`.
+	 */
+	$block_template = apply_filters( 'pre_get_block_file_template', null, $id, $template_type );
+	if ( ! is_null( $block_template ) ) {
+		return $block_template;
+	}
+
+	$parts = explode( '//', $id, 2 );
+	if ( count( $parts ) < 2 ) {
+		/** This filter is documented at the end of this function */
+		return apply_filters( 'get_block_file_template', null, $id, $template_type );
+	}
+	list( $theme, $slug ) = $parts;
+
+	if ( wp_get_theme()->get_stylesheet() !== $theme ) {
+		/** This filter is documented at the end of this function */
+		return apply_filters( 'get_block_file_template', null, $id, $template_type );
+	}
+
+	$template_file = _get_block_template_file( $template_type, $slug );
+	if ( null === $template_file ) {
+		/** This filter is documented at the end of this function */
+		return apply_filters( 'get_block_file_template', null, $id, $template_type );
+	}
+
+	$block_template = _build_block_template_result_from_file( $template_file, $template_type );
+
+	/**
+	 * Filters the array of queried block templates array after they've been fetched.
+	 *
+	 * @since 5.9.0
+	 *
+	 * @param WP_Block_Template $block_template The found block template.
+	 * @param string            $id             Template unique identifier (example: theme_slug//template_slug).
+	 * @param array             $template_type  Template type: `'wp_template'` or '`wp_template_part'`.
+	 */
+	return apply_filters( 'get_block_file_template', $block_template, $id, $template_type );
+}
+
+/**
+ * Print a template-part.
+ *
+ * @since 5.9.0
+ *
+ * @param string $part The template-part to print. Use "header" or "footer".
+ */
+function block_template_part( $part ) {
+	$template_part = get_block_template( get_stylesheet() . '//' . $part, 'wp_template_part' );
+	if ( ! $template_part || empty( $template_part->content ) ) {
+		return;
+	}
+	echo do_blocks( $template_part->content );
+}
+
+/**
+ * Print the header template-part.
+ *
+ * @since 5.9.0
+ */
+function block_header_area() {
+	block_template_part( 'header' );
+}
+
+/**
+ * Print the footer template-part.
+ *
+ * @since 5.9.0
+ */
+function block_footer_area() {
+	block_template_part( 'footer' );
 }

wp-includes/blocks.php

@@ -1154,6 +1154,8 @@ function build_query_vars_from_query_block( $block, $page ) {
  *
  * It's used in QueryPaginationNext and QueryPaginationPrevious blocks.
  *
+ * @since 5.9.0
+ *
  * @param WP_Block $block   Block instance.
  * @param boolean  $is_next Flag for hanlding `next/previous` blocks.
  *

wp-includes/blocks/index.php

@@ -37,6 +37,7 @@ require ABSPATH . WPINC . '/blocks/site-logo.php';
 require ABSPATH . WPINC . '/blocks/site-title.php';
 require ABSPATH . WPINC . '/blocks/social-link.php';
 require ABSPATH . WPINC . '/blocks/tag-cloud.php';
+require ABSPATH . WPINC . '/blocks/template-part.php';
 
 /**
  * Registers core block types using metadata files.

wp-includes/blocks/template-part.php

@@ -0,0 +1,155 @@
+<?php
+/**
+ * Server-side rendering of the `core/template-part` block.
+ *
+ * @package WordPress
+ */
+
+/**
+ * Renders the `core/template-part` block on the server.
+ *
+ * @param array $attributes The block attributes.
+ *
+ * @return string The render.
+ */
+function render_block_core_template_part( $attributes ) {
+	static $seen_ids = array();
+
+	$template_part_id = null;
+	$content          = null;
+	$area             = WP_TEMPLATE_PART_AREA_UNCATEGORIZED;
+
+	if (
+		isset( $attributes['slug'] ) &&
+		isset( $attributes['theme'] ) &&
+		wp_get_theme()->get_stylesheet() === $attributes['theme']
+	) {
+		$template_part_id    = $attributes['theme'] . '//' . $attributes['slug'];
+		$template_part_query = new WP_Query(
+			array(
+				'post_type'      => 'wp_template_part',
+				'post_status'    => 'publish',
+				'post_name__in'  => array( $attributes['slug'] ),
+				'tax_query'      => array(
+					array(
+						'taxonomy' => 'wp_theme',
+						'field'    => 'slug',
+						'terms'    => $attributes['theme'],
+					),
+				),
+				'posts_per_page' => 1,
+				'no_found_rows'  => true,
+			)
+		);
+		$template_part_post  = $template_part_query->have_posts() ? $template_part_query->next_post() : null;
+		if ( $template_part_post ) {
+			// A published post might already exist if this template part was customized elsewhere
+			// or if it's part of a customized template.
+			$content    = $template_part_post->post_content;
+			$area_terms = get_the_terms( $template_part_post, 'wp_template_part_area' );
+			if ( ! is_wp_error( $area_terms ) && false !== $area_terms ) {
+				$area = $area_terms[0]->name;
+			}
+		} else {
+			// Else, if the template part was provided by the active theme,
+			// render the corresponding file content.
+			$template_part_file_path = get_theme_file_path( '/block-template-parts/' . $attributes['slug'] . '.html' );
+			if ( 0 === validate_file( $attributes['slug'] ) && file_exists( $template_part_file_path ) ) {
+				$content = _inject_theme_attribute_in_block_template_content( file_get_contents( $template_part_file_path ) );
+			}
+		}
+	}
+
+	if ( is_null( $content ) && is_user_logged_in() ) {
+		if ( ! isset( $attributes['slug'] ) ) {
+			// If there is no slug this is a placeholder and we dont want to return any message.
+			return;
+		}
+		return sprintf(
+			/* translators: %s: Template part slug. */
+			__( 'Template part has been deleted or is unavailable: %s' ),
+			$attributes['slug']
+		);
+	}
+
+	if ( isset( $seen_ids[ $template_part_id ] ) ) {
+		// WP_DEBUG_DISPLAY must only be honored when WP_DEBUG. This precedent
+		// is set in `wp_debug_mode()`.
+		$is_debug = defined( 'WP_DEBUG' ) && WP_DEBUG &&
+			defined( 'WP_DEBUG_DISPLAY' ) && WP_DEBUG_DISPLAY;
+
+		return $is_debug ?
+			// translators: Visible only in the front end, this warning takes the place of a faulty block.
+			__( '[block rendering halted]' ) :
+			'';
+	}
+
+	// Run through the actions that are typically taken on the_content.
+	$seen_ids[ $template_part_id ] = true;
+	$content                       = do_blocks( $content );
+	unset( $seen_ids[ $template_part_id ] );
+	$content = wptexturize( $content );
+	$content = convert_smilies( $content );
+	$content = shortcode_unautop( $content );
+	$content = wp_filter_content_tags( $content );
+	$content = do_shortcode( $content );
+
+	// Handle embeds for block template parts.
+	global $wp_embed;
+	$content = $wp_embed->autoembed( $content );
+
+	if ( empty( $attributes['tagName'] ) ) {
+		$defined_areas = get_allowed_block_template_part_areas();
+		$area_tag      = 'div';
+		foreach ( $defined_areas as $defined_area ) {
+			if ( $defined_area['area'] === $area && isset( $defined_area['area_tag'] ) ) {
+				$area_tag = $defined_area['area_tag'];
+			}
+		}
+		$html_tag = $area_tag;
+	} else {
+		$html_tag = esc_attr( $attributes['tagName'] );
+	}
+	$wrapper_attributes = get_block_wrapper_attributes();
+
+	return "<$html_tag $wrapper_attributes>" . str_replace( ']]>', ']]&gt;', $content ) . "</$html_tag>";
+}
+
+/**
+ * Returns an array of variation objects for the template part block.
+ *
+ * @return array Array containing the block variation objects.
+ */
+function build_template_part_block_variations() {
+	$variations    = array();
+	$defined_areas = get_allowed_block_template_part_areas();
+	foreach ( $defined_areas as $area ) {
+		if ( 'uncategorized' !== $area['area'] ) {
+			$variations[] = array(
+				'name'        => $area['area'],
+				'title'       => $area['label'],
+				'description' => $area['description'],
+				'attributes'  => array(
+					'area' => $area['area'],
+				),
+				'scope'       => array( 'inserter' ),
+				'icon'        => $area['icon'],
+			);
+		}
+	}
+	return $variations;
+}
+
+/**
+ * Registers the `core/template-part` block on the server.
+ */
+function register_block_core_template_part() {
+	register_block_type_from_metadata(
+		__DIR__ . '/template-part',
+		array(
+			'render_callback' => 'render_block_core_template_part',
+			'variations'      => build_template_part_block_variations(),
+		)
+	);
+}
+add_action( 'init', 'register_block_core_template_part' );

wp-includes/blocks/template-part/block.json

@@ -0,0 +1,35 @@
+{
+	"apiVersion": 2,
+	"name": "core/template-part",
+	"title": "Template Part",
+	"category": "theme",
+	"description": "Edit the different global regions of your site, like the header, footer, sidebar, or create your own.",
+	"textdomain": "default",
+	"attributes": {
+		"slug": {
+			"type": "string"
+		},
+		"theme": {
+			"type": "string"
+		},
+		"tagName": {
+			"type": "string"
+		},
+		"area": {
+			"type": "string"
+		}
+	},
+	"supports": {
+		"align": true,
+		"html": false,
+		"color": {
+			"gradients": true,
+			"link": true
+		},
+		"spacing": {
+			"padding": true
+		},
+		"__experimentalLayout": true
+	},
+	"editorStyle": "wp-block-template-part-editor"
+}

wp-includes/blocks/template-part/editor-rtl.css

@@ -0,0 +1,138 @@
+/**
+ * Colors
+ */
+/**
+ * Breakpoints & Media Queries
+ */
+/**
+ * SCSS Variables.
+ *
+ * Please use variables from this sheet to ensure consistency across the UI.
+ * Don't add to this sheet unless you're pretty sure the value will be reused in many places.
+ * For example, don't add rules to this sheet that affect block visuals. It's purely for UI.
+ */
+/**
+ * Colors
+ */
+/**
+ * Fonts & basic variables.
+ */
+/**
+ * Grid System.
+ * https://make.wordpress.org/design/2019/10/31/proposal-a-consistent-spacing-system-for-wordpress/
+ */
+/**
+ * Dimensions.
+ */
+/**
+ * Shadows.
+ */
+/**
+ * Editor widths.
+ */
+/**
+ * Block & Editor UI.
+ */
+/**
+ * Block paddings.
+ */
+/**
+ * React Native specific.
+ * These variables do not appear to be used anywhere else.
+ */
+/**
+*  Converts a hex value into the rgb equivalent.
+*
+* @param {string} hex - the hexadecimal value to convert
+* @return {string} comma separated rgb values
+*/
+/**
+ * Breakpoint mixins
+ */
+/**
+ * Long content fade mixin
+ *
+ * Creates a fading overlay to signify that the content is longer
+ * than the space allows.
+ */
+/**
+ * Focus styles.
+ */
+/**
+ * Applies editor left position to the selector passed as argument
+ */
+/**
+ * Styles that are reused verbatim in a few places
+ */
+/**
+ * Allows users to opt-out of animations via OS-level preferences.
+ */
+/**
+ * Reset default styles for JavaScript UI based pages.
+ * This is a WP-admin agnostic reset
+ */
+/**
+ * Reset the WP Admin page styles for Gutenberg-like pages.
+ */
+.wp-block-template-part__placeholder-preview-dropdown-content .components-popover__content,
+.wp-block-template-part__preview-dropdown-content .components-popover__content {
+  min-width: 320px;
+  padding: 0;
+}
+
+.wp-block-template-part__selection-preview-search-form {
+  border-bottom: 1px solid #ddd;
+}
+
+.wp-block-template-part__selection-preview-container {
+  background: #fff;
+  padding-bottom: 16px;
+}
+.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-preview-item {
+  border-radius: 2px;
+  cursor: pointer;
+  margin-top: 16px;
+  transition: all 0.05s ease-in-out;
+  border: 1px solid #ddd;
+  width: 100%;
+  background-color: #fff;
+}
+.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-preview-item:hover {
+  border: 1px solid var(--wp-admin-theme-color);
+}
+.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-preview-item:focus {
+  box-shadow: inset 0 0 0 1px #fff, 0 0 0 var(--wp-admin-border-width-focus) var(--wp-admin-theme-color);
+  outline: 2px solid transparent;
+}
+.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-preview-item.is-placeholder {
+  min-height: 100px;
+}
+.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-preview-item .block-editor-block-preview__container {
+  border-bottom: 1px solid #ddd;
+}
+.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-preview-item-title {
+  padding: 4px;
+  font-size: 12px;
+  text-align: right;
+}
+.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-panel-group-header {
+  padding: 16px 16px 0;
+}
+.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-panel-group-content {
+  padding: 0 16px;
+}
+.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-panel-group-title {
+  color: var(--wp-admin-theme-color);
+  text-transform: uppercase;
+  font-size: 11px;
+  font-weight: 500;
+}
+
+.wp-block-template-part__placeholder-create-new__title-form .wp-block-template-part__placeholder-create-new__title-form-actions {
+  padding-top: 12px;
+  display: flex;
+  justify-content: flex-end;
+}
+.wp-block-template-part__placeholder-create-new__title-form .wp-block-template-part__placeholder-create-new__title-form-actions .components-flex-item {
+  margin-right: 12px;
+}

wp-includes/blocks/template-part/editor-rtl.min.css

@@ -0,0 +1 @@
+.wp-block-template-part__placeholder-preview-dropdown-content .components-popover__content,.wp-block-template-part__preview-dropdown-content .components-popover__content{min-width:320px;padding:0}.wp-block-template-part__selection-preview-search-form{border-bottom:1px solid #ddd}.wp-block-template-part__selection-preview-container{background:#fff;padding-bottom:16px}.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-preview-item{border-radius:2px;cursor:pointer;margin-top:16px;transition:all .05s ease-in-out;border:1px solid #ddd;width:100%;background-color:#fff}.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-preview-item:hover{border:1px solid var(--wp-admin-theme-color)}.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-preview-item:focus{box-shadow:inset 0 0 0 1px #fff,0 0 0 var(--wp-admin-border-width-focus) var(--wp-admin-theme-color);outline:2px solid transparent}.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-preview-item.is-placeholder{min-height:100px}.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-preview-item .block-editor-block-preview__container{border-bottom:1px solid #ddd}.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-preview-item-title{padding:4px;font-size:12px;text-align:right}.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-panel-group-header{padding:16px 16px 0}.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-panel-group-content{padding:0 16px}.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-panel-group-title{color:var(--wp-admin-theme-color);text-transform:uppercase;font-size:11px;font-weight:500}.wp-block-template-part__placeholder-create-new__title-form .wp-block-template-part__placeholder-create-new__title-form-actions{padding-top:12px;display:flex;justify-content:flex-end}.wp-block-template-part__placeholder-create-new__title-form .wp-block-template-part__placeholder-create-new__title-form-actions .components-flex-item{margin-right:12px}

wp-includes/blocks/template-part/editor.css

@@ -0,0 +1,138 @@
+/**
+ * Colors
+ */
+/**
+ * Breakpoints & Media Queries
+ */
+/**
+ * SCSS Variables.
+ *
+ * Please use variables from this sheet to ensure consistency across the UI.
+ * Don't add to this sheet unless you're pretty sure the value will be reused in many places.
+ * For example, don't add rules to this sheet that affect block visuals. It's purely for UI.
+ */
+/**
+ * Colors
+ */
+/**
+ * Fonts & basic variables.
+ */
+/**
+ * Grid System.
+ * https://make.wordpress.org/design/2019/10/31/proposal-a-consistent-spacing-system-for-wordpress/
+ */
+/**
+ * Dimensions.
+ */
+/**
+ * Shadows.
+ */
+/**
+ * Editor widths.
+ */
+/**
+ * Block & Editor UI.
+ */
+/**
+ * Block paddings.
+ */
+/**
+ * React Native specific.
+ * These variables do not appear to be used anywhere else.
+ */
+/**
+*  Converts a hex value into the rgb equivalent.
+*
+* @param {string} hex - the hexadecimal value to convert
+* @return {string} comma separated rgb values
+*/
+/**
+ * Breakpoint mixins
+ */
+/**
+ * Long content fade mixin
+ *
+ * Creates a fading overlay to signify that the content is longer
+ * than the space allows.
+ */
+/**
+ * Focus styles.
+ */
+/**
+ * Applies editor left position to the selector passed as argument
+ */
+/**
+ * Styles that are reused verbatim in a few places
+ */
+/**
+ * Allows users to opt-out of animations via OS-level preferences.
+ */
+/**
+ * Reset default styles for JavaScript UI based pages.
+ * This is a WP-admin agnostic reset
+ */
+/**
+ * Reset the WP Admin page styles for Gutenberg-like pages.
+ */
+.wp-block-template-part__placeholder-preview-dropdown-content .components-popover__content,
+.wp-block-template-part__preview-dropdown-content .components-popover__content {
+  min-width: 320px;
+  padding: 0;
+}
+
+.wp-block-template-part__selection-preview-search-form {
+  border-bottom: 1px solid #ddd;
+}
+
+.wp-block-template-part__selection-preview-container {
+  background: #fff;
+  padding-bottom: 16px;
+}
+.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-preview-item {
+  border-radius: 2px;
+  cursor: pointer;
+  margin-top: 16px;
+  transition: all 0.05s ease-in-out;
+  border: 1px solid #ddd;
+  width: 100%;
+  background-color: #fff;
+}
+.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-preview-item:hover {
+  border: 1px solid var(--wp-admin-theme-color);
+}
+.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-preview-item:focus {
+  box-shadow: inset 0 0 0 1px #fff, 0 0 0 var(--wp-admin-border-width-focus) var(--wp-admin-theme-color);
+  outline: 2px solid transparent;
+}
+.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-preview-item.is-placeholder {
+  min-height: 100px;
+}
+.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-preview-item .block-editor-block-preview__container {
+  border-bottom: 1px solid #ddd;
+}
+.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-preview-item-title {
+  padding: 4px;
+  font-size: 12px;
+  text-align: left;
+}
+.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-panel-group-header {
+  padding: 16px 16px 0;
+}
+.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-panel-group-content {
+  padding: 0 16px;
+}
+.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-panel-group-title {
+  color: var(--wp-admin-theme-color);
+  text-transform: uppercase;
+  font-size: 11px;
+  font-weight: 500;
+}
+
+.wp-block-template-part__placeholder-create-new__title-form .wp-block-template-part__placeholder-create-new__title-form-actions {
+  padding-top: 12px;
+  display: flex;
+  justify-content: flex-end;
+}
+.wp-block-template-part__placeholder-create-new__title-form .wp-block-template-part__placeholder-create-new__title-form-actions .components-flex-item {
+  margin-left: 12px;
+}

wp-includes/blocks/template-part/editor.min.css

@@ -0,0 +1 @@
+.wp-block-template-part__placeholder-preview-dropdown-content .components-popover__content,.wp-block-template-part__preview-dropdown-content .components-popover__content{min-width:320px;padding:0}.wp-block-template-part__selection-preview-search-form{border-bottom:1px solid #ddd}.wp-block-template-part__selection-preview-container{background:#fff;padding-bottom:16px}.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-preview-item{border-radius:2px;cursor:pointer;margin-top:16px;transition:all .05s ease-in-out;border:1px solid #ddd;width:100%;background-color:#fff}.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-preview-item:hover{border:1px solid var(--wp-admin-theme-color)}.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-preview-item:focus{box-shadow:inset 0 0 0 1px #fff,0 0 0 var(--wp-admin-border-width-focus) var(--wp-admin-theme-color);outline:2px solid transparent}.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-preview-item.is-placeholder{min-height:100px}.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-preview-item .block-editor-block-preview__container{border-bottom:1px solid #ddd}.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-preview-item-title{padding:4px;font-size:12px;text-align:left}.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-panel-group-header{padding:16px 16px 0}.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-panel-group-content{padding:0 16px}.wp-block-template-part__selection-preview-container .wp-block-template-part__selection-panel-group-title{color:var(--wp-admin-theme-color);text-transform:uppercase;font-size:11px;font-weight:500}.wp-block-template-part__placeholder-create-new__title-form .wp-block-template-part__placeholder-create-new__title-form-actions{padding-top:12px;display:flex;justify-content:flex-end}.wp-block-template-part__placeholder-create-new__title-form .wp-block-template-part__placeholder-create-new__title-form-actions .components-flex-item{margin-left:12px}

wp-includes/blocks/template-part/theme-rtl.css

@@ -0,0 +1,81 @@
+/**
+ * Colors
+ */
+/**
+ * Breakpoints & Media Queries
+ */
+/**
+ * SCSS Variables.
+ *
+ * Please use variables from this sheet to ensure consistency across the UI.
+ * Don't add to this sheet unless you're pretty sure the value will be reused in many places.
+ * For example, don't add rules to this sheet that affect block visuals. It's purely for UI.
+ */
+/**
+ * Colors
+ */
+/**
+ * Fonts & basic variables.
+ */
+/**
+ * Grid System.
+ * https://make.wordpress.org/design/2019/10/31/proposal-a-consistent-spacing-system-for-wordpress/
+ */
+/**
+ * Dimensions.
+ */
+/**
+ * Shadows.
+ */
+/**
+ * Editor widths.
+ */
+/**
+ * Block & Editor UI.
+ */
+/**
+ * Block paddings.
+ */
+/**
+ * React Native specific.
+ * These variables do not appear to be used anywhere else.
+ */
+/**
+*  Converts a hex value into the rgb equivalent.
+*
+* @param {string} hex - the hexadecimal value to convert
+* @return {string} comma separated rgb values
+*/
+/**
+ * Breakpoint mixins
+ */
+/**
+ * Long content fade mixin
+ *
+ * Creates a fading overlay to signify that the content is longer
+ * than the space allows.
+ */
+/**
+ * Focus styles.
+ */
+/**
+ * Applies editor left position to the selector passed as argument
+ */
+/**
+ * Styles that are reused verbatim in a few places
+ */
+/**
+ * Allows users to opt-out of animations via OS-level preferences.
+ */
+/**
+ * Reset default styles for JavaScript UI based pages.
+ * This is a WP-admin agnostic reset
+ */
+/**
+ * Reset the WP Admin page styles for Gutenberg-like pages.
+ */
+.wp-block-template-part.has-background {
+  padding: 1.25em 2.375em;
+  margin-top: 0;
+  margin-bottom: 0;
+}

wp-includes/blocks/template-part/theme-rtl.min.css

@@ -0,0 +1 @@
+.wp-block-template-part.has-background{padding:1.25em 2.375em;margin-top:0;margin-bottom:0}

wp-includes/blocks/template-part/theme.css

@@ -0,0 +1,81 @@
+/**
+ * Colors
+ */
+/**
+ * Breakpoints & Media Queries
+ */
+/**
+ * SCSS Variables.
+ *
+ * Please use variables from this sheet to ensure consistency across the UI.
+ * Don't add to this sheet unless you're pretty sure the value will be reused in many places.
+ * For example, don't add rules to this sheet that affect block visuals. It's purely for UI.
+ */
+/**
+ * Colors
+ */
+/**
+ * Fonts & basic variables.
+ */
+/**
+ * Grid System.
+ * https://make.wordpress.org/design/2019/10/31/proposal-a-consistent-spacing-system-for-wordpress/
+ */
+/**
+ * Dimensions.
+ */
+/**
+ * Shadows.
+ */
+/**
+ * Editor widths.
+ */
+/**
+ * Block & Editor UI.
+ */
+/**
+ * Block paddings.
+ */
+/**
+ * React Native specific.
+ * These variables do not appear to be used anywhere else.
+ */
+/**
+*  Converts a hex value into the rgb equivalent.
+*
+* @param {string} hex - the hexadecimal value to convert
+* @return {string} comma separated rgb values
+*/
+/**
+ * Breakpoint mixins
+ */
+/**
+ * Long content fade mixin
+ *
+ * Creates a fading overlay to signify that the content is longer
+ * than the space allows.
+ */
+/**
+ * Focus styles.
+ */
+/**
+ * Applies editor left position to the selector passed as argument
+ */
+/**
+ * Styles that are reused verbatim in a few places
+ */
+/**
+ * Allows users to opt-out of animations via OS-level preferences.
+ */
+/**
+ * Reset default styles for JavaScript UI based pages.
+ * This is a WP-admin agnostic reset
+ */
+/**
+ * Reset the WP Admin page styles for Gutenberg-like pages.
+ */
+.wp-block-template-part.has-background {
+  padding: 1.25em 2.375em;
+  margin-top: 0;
+  margin-bottom: 0;
+}

wp-includes/blocks/template-part/theme.min.css

@@ -0,0 +1 @@
+.wp-block-template-part.has-background{padding:1.25em 2.375em;margin-top:0;margin-bottom:0}

wp-includes/class-wp-block-template.php

@@ -100,4 +100,13 @@ class WP_Block_Template {
 	 * @var boolean
 	 */
 	public $has_theme_file;
+
+	/**
+	 * Whether a template is a custom template.
+	 *
+	 * @since 5.9.0
+	 *
+	 * @var boolean
+	 */
+	public $is_custom = true;
 }

wp-includes/class-wp-theme-json.php

@@ -601,7 +601,7 @@ class WP_Theme_JSON {
 	 */
 	public function get_custom_templates() {
 		$custom_templates = array();
-		if ( ! isset( $this->theme_json['customTemplates'] ) ) {
+		if ( ! isset( $this->theme_json['customTemplates'] ) || ! is_array( $this->theme_json['customTemplates'] ) ) {
 			return $custom_templates;
 		}
 
@@ -625,7 +625,7 @@ class WP_Theme_JSON {
 	 */
 	public function get_template_parts() {
 		$template_parts = array();
-		if ( ! isset( $this->theme_json['templateParts'] ) ) {
+		if ( ! isset( $this->theme_json['templateParts'] ) || ! is_array( $this->theme_json['templateParts'] ) ) {
 			return $template_parts;
 		}
 

wp-includes/default-filters.php

@@ -664,6 +664,7 @@ add_filter( 'user_has_cap', 'wp_maybe_grant_site_health_caps', 1, 4 );
 // Block Templates CPT and Rendering
 add_filter( 'render_block_context', '_block_template_render_without_post_block_context' );
 add_filter( 'pre_wp_unique_post_slug', 'wp_filter_wp_template_unique_post_slug', 10, 5 );
+add_action( 'save_post_wp_template_part', 'wp_set_unique_slug_on_create_template_part' );
 add_action( 'wp_footer', 'the_block_template_skip_link' );
 add_action( 'setup_theme', 'wp_enable_block_templates' );
 

wp-includes/post.php

@@ -365,6 +365,64 @@ function create_initial_post_types() {
 		)
 	);
 
+	register_post_type(
+		'wp_template_part',
+		array(
+			'labels'                => array(
+				'name'                  => __( 'Template Parts' ),
+				'singular_name'         => __( 'Template Part' ),
+				'add_new'               => _x( 'Add New', 'Template Part' ),
+				'add_new_item'          => __( 'Add New Template Part' ),
+				'new_item'              => __( 'New Template Part' ),
+				'edit_item'             => __( 'Edit Template Part' ),
+				'view_item'             => __( 'View Template Part' ),
+				'all_items'             => __( 'All Template Parts' ),
+				'search_items'          => __( 'Search Template Parts' ),
+				'parent_item_colon'     => __( 'Parent Template Part:' ),
+				'not_found'             => __( 'No template parts found.' ),
+				'not_found_in_trash'    => __( 'No template parts found in Trash.' ),
+				'archives'              => __( 'Template part archives' ),
+				'insert_into_item'      => __( 'Insert into template part' ),
+				'uploaded_to_this_item' => __( 'Uploaded to this template part' ),
+				'filter_items_list'     => __( 'Filter template parts list' ),
+				'items_list_navigation' => __( 'Template parts list navigation' ),
+				'items_list'            => __( 'Template parts list' ),
+			),
+			'description'           => __( 'Template parts to include in your templates.' ),
+			'public'                => false,
+			'_builtin'              => true, /* internal use only. don't use this when registering your own post type. */
+			'has_archive'           => false,
+			'show_ui'               => false,
+			'show_in_menu'          => false,
+			'show_in_rest'          => true,
+			'rewrite'               => false,
+			'rest_base'             => 'template-parts',
+			'rest_controller_class' => 'WP_REST_Templates_Controller',
+			'map_meta_cap'          => true,
+			'capabilities'          => array(
+				'create_posts'           => 'edit_theme_options',
+				'delete_posts'           => 'edit_theme_options',
+				'delete_others_posts'    => 'edit_theme_options',
+				'delete_private_posts'   => 'edit_theme_options',
+				'delete_published_posts' => 'edit_theme_options',
+				'edit_posts'             => 'edit_theme_options',
+				'edit_others_posts'      => 'edit_theme_options',
+				'edit_private_posts'     => 'edit_theme_options',
+				'edit_published_posts'   => 'edit_theme_options',
+				'publish_posts'          => 'edit_theme_options',
+				'read'                   => 'edit_theme_options',
+				'read_private_posts'     => 'edit_theme_options',
+			),
+			'supports'              => array(
+				'title',
+				'slug',
+				'excerpt',
+				'editor',
+				'revisions',
+			),
+		)
+	);
+
 	register_post_type(
 		'wp_global_styles',
 		array(

wp-includes/rest-api/endpoints/class-wp-rest-templates-controller.php

@@ -156,6 +156,9 @@ class WP_REST_Templates_Controller extends WP_REST_Controller {
 		if ( isset( $request['area'] ) ) {
 			$query['area'] = $request['area'];
 		}
+		if ( isset( $request['post_type'] ) ) {
+			$query['post_type'] = $request['post_type'];
+		}
 
 		$templates = array();
 		foreach ( get_block_templates( $query, $this->post_type ) as $template ) {
@@ -187,7 +190,11 @@ class WP_REST_Templates_Controller extends WP_REST_Controller {
 	 * @return WP_REST_Response|WP_Error
 	 */
 	public function get_item( $request ) {
-		$template = get_block_template( $request['id'], $this->post_type );
+		if ( isset( $request['source'] ) && 'theme' === $request['source'] ) {
+			$template = get_block_file_template( $request['id'], $this->post_type );
+		} else {
+			$template = get_block_template( $request['id'], $this->post_type );
+		}
 
 		if ( ! $template ) {
 			return new WP_Error( 'rest_template_not_found', __( 'No templates exist with that id.' ), array( 'status' => 404 ) );
@@ -222,6 +229,11 @@ class WP_REST_Templates_Controller extends WP_REST_Controller {
 			return new WP_Error( 'rest_template_not_found', __( 'No templates exist with that id.' ), array( 'status' => 404 ) );
 		}
 
+		if ( isset( $request['source'] ) && 'theme' === $request['source'] ) {
+			wp_delete_post( $template->wp_id, true );
+			return $this->prepare_item_for_response( get_block_file_template( $request['id'], $this->post_type ), $request );
+		}
+
 		$changes = $this->prepare_item_for_database( $request );
 
 		if ( 'custom' === $template->source ) {
@@ -395,6 +407,16 @@ class WP_REST_Templates_Controller extends WP_REST_Controller {
 			$changes->post_excerpt = $template->description;
 		}
 
+		if ( 'wp_template_part' === $this->post_type ) {
+			if ( isset( $request['area'] ) ) {
+				$changes->tax_input['wp_template_part_area'] = _filter_block_template_part_area( $request['area'] );
+			} elseif ( null !== $template && 'custom' !== $template->source && $template->area ) {
+				$changes->tax_input['wp_template_part_area'] = _filter_block_template_part_area( $template->area );
+			} elseif ( ! $template->area ) {
+				$changes->tax_input['wp_template_part_area'] = WP_TEMPLATE_PART_AREA_UNCATEGORIZED;
+			}
+		}
+
 		return $changes;
 	}
 
@@ -502,16 +524,25 @@ class WP_REST_Templates_Controller extends WP_REST_Controller {
 	 * Retrieves the query params for the posts collection.
 	 *
 	 * @since 5.8.0
+	 * @since 5.9.0 Added `'area'` and `'post_type'`.
 	 *
 	 * @return array Collection parameters.
 	 */
 	public function get_collection_params() {
 		return array(
-			'context' => $this->get_context_param(),
+			'context'   => $this->get_context_param(),
-			'wp_id'   => array(
+			'wp_id'     => array(
 				'description' => __( 'Limit to the specified post id.' ),
 				'type'        => 'integer',
 			),
+			'area'      => array(
+				'description' => __( 'Limit to the specified template part area.' ),
+				'type'        => 'string',
+			),
+			'post_type' => array(
+				'description' => __( 'Post type to get the templates for.' ),
+				'type'        => 'string',
+			),
 		);
 	}
 
@@ -519,6 +550,7 @@ class WP_REST_Templates_Controller extends WP_REST_Controller {
 	 * Retrieves the block type' schema, conforming to JSON Schema.
 	 *
 	 * @since 5.8.0
+	 * @since 5.9.0 Added `'area'`.
 	 *
 	 * @return array Item schema data.
 	 */
@@ -596,6 +628,14 @@ class WP_REST_Templates_Controller extends WP_REST_Controller {
 			),
 		);
 
+		if ( 'wp_template_part' === $this->post_type ) {
+			$schema['properties']['area'] = array(
+				'description' => __( 'Where the template part is intended for use (header, footer, etc.)' ),
+				'type'        => 'string',
+				'context'     => array( 'embed', 'view', 'edit' ),
+			);
+		}
+
 		$this->schema = $schema;
 
 		return $this->add_additional_fields_schema( $this->schema );

wp-includes/taxonomy.php

@@ -18,6 +18,7 @@
  * avoid registering rewrite rules before the {@see 'init'} action.
  *
  * @since 2.8.0
+ * @since 5.9.0 Added `'wp_template_part_area'` taxonomy.
  *
  * @global WP_Rewrite $wp_rewrite WordPress rewrite component.
  */
@@ -175,7 +176,7 @@ function create_initial_taxonomies() {
 
 	register_taxonomy(
 		'wp_theme',
-		array( 'wp_template', 'wp_global_styles' ),
+		array( 'wp_template', 'wp_template_part', 'wp_global_styles' ),
 		array(
 			'public'            => false,
 			'hierarchical'      => false,
@@ -191,6 +192,25 @@ function create_initial_taxonomies() {
 			'show_in_rest'      => false,
 		)
 	);
+
+	register_taxonomy(
+		'wp_template_part_area',
+		array( 'wp_template_part' ),
+		array(
+			'public'            => false,
+			'hierarchical'      => false,
+			'labels'            => array(
+				'name'          => __( 'Template Part Areas' ),
+				'singular_name' => __( 'Template Part Area' ),
+			),
+			'query_var'         => false,
+			'rewrite'           => false,
+			'show_ui'           => false,
+			'_builtin'          => true,
+			'show_in_nav_menus' => false,
+			'show_in_rest'      => false,
+		)
+	);
 }
 
 /**

wp-includes/theme-templates.php

@@ -1,5 +1,35 @@
 <?php
 
+/**
+ * Sets a custom slug when creating auto-draft template parts.
+ *
+ * This is only needed for auto-drafts created by the regular WP editor.
+ * If this page is to be removed, this won't be necessary.
+ *
+ * @since 5.9.0
+ *
+ */
+function wp_set_unique_slug_on_create_template_part( $post_id ) {
+	$post = get_post( $post_id );
+	if ( 'auto-draft' !== $post->post_status ) {
+		return;
+	}
+
+	if ( ! $post->post_name ) {
+		wp_update_post(
+			array(
+				'ID'        => $post_id,
+				'post_name' => 'custom_slug_' . uniqid(),
+			)
+		);
+	}
+
+	$terms = get_the_terms( $post_id, 'wp_theme' );
+	if ( ! is_array( $terms ) || ! count( $terms ) ) {
+		wp_set_post_terms( $post_id, wp_get_theme()->get_stylesheet(), 'wp_theme' );
+	}
+}
+
 /**
  * Generates a unique slug for templates.
  *
@@ -14,7 +44,7 @@
  * @return string The original, desired slug.
  */
 function wp_filter_wp_template_unique_post_slug( $override_slug, $slug, $post_ID, $post_status, $post_type ) {
-	if ( 'wp_template' !== $post_type ) {
+	if ( 'wp_template' !== $post_type && 'wp_template_part' !== $post_type ) {
 		return $override_slug;
 	}
 

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.9-alpha-52061';
+$wp_version = '5.9-alpha-52062';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.