From 9dc7058be9be89e4484a2aac8a05fe605976ec2b Mon Sep 17 00:00:00 2001
From: TimothyBlynJacobs <TimothyBlynJacobs@git.wordpress.org>
Date: Thu, 25 Jun 2020 22:13:10 +0000
Subject: [PATCH] Themes: Introduce register_theme_feature API.

Currently themes can declare support for a given feature by using add_theme_support(). This commit adds a register_theme_feature() API that allows plugins and WordPress Core to declare a list of available features that themes can support.

The REST API uses this to expose a theme's supported features if the feature has been registered with "show_in_rest" set to true.

Props kadamwhite, spacedmonkey, williampatton, desrosj, TimothyBlynJacobs.
Fixes #49406.

Built from https://develop.svn.wordpress.org/trunk@48171


git-svn-id: http://core.svn.wordpress.org/trunk@47940 1a063a9b-81f0-0310-95a4-ce76da25c4cd
---
 wp-includes/default-filters.php               |   1 +
 wp-includes/rest-api.php                      |  32 ++
 .../class-wp-rest-themes-controller.php       | 361 +++---------
 wp-includes/theme.php                         | 518 ++++++++++++++++++
 wp-includes/version.php                       |   2 +-
 5 files changed, 619 insertions(+), 295 deletions(-)

diff --git a/wp-includes/default-filters.php b/wp-includes/default-filters.php
index 18c91c0a4e..0a5a46695a 100644
--- a/wp-includes/default-filters.php
+++ b/wp-includes/default-filters.php
@@ -470,6 +470,7 @@ add_action( 'transition_post_status', '_wp_customize_publish_changeset', 10, 3 )
 add_action( 'admin_enqueue_scripts', '_wp_customize_loader_settings' );
 add_action( 'delete_attachment', '_delete_attachment_theme_mod' );
 add_action( 'transition_post_status', '_wp_keep_alive_customize_changeset_dependent_auto_drafts', 20, 3 );
+add_action( 'setup_theme', 'create_initial_theme_features', 0 );
 
 // Calendar widget cache.
 add_action( 'save_post', 'delete_get_calendar_cache' );
diff --git a/wp-includes/rest-api.php b/wp-includes/rest-api.php
index ac422b27aa..43569e3c1a 100644
--- a/wp-includes/rest-api.php
+++ b/wp-includes/rest-api.php
@@ -1779,3 +1779,35 @@ function rest_filter_response_by_context( $data, $schema, $context ) {
 
 	return $data;
 }
+
+/**
+ * Sets the "additionalProperties" to false by default for all object definitions in the schema.
+ *
+ * @since 5.5.0
+ *
+ * @param array $schema The schema to modify.
+ * @return array The modified schema.
+ */
+function rest_default_additional_properties_to_false( $schema ) {
+	$type = (array) $schema['type'];
+
+	if ( in_array( 'object', $type, true ) ) {
+		if ( isset( $schema['properties'] ) ) {
+			foreach ( $schema['properties'] as $key => $child_schema ) {
+				$schema['properties'][ $key ] = rest_default_additional_properties_to_false( $child_schema );
+			}
+		}
+
+		if ( ! isset( $schema['additionalProperties'] ) ) {
+			$schema['additionalProperties'] = false;
+		}
+	}
+
+	if ( in_array( 'array', $type, true ) ) {
+		if ( isset( $schema['items'] ) ) {
+			$schema['items'] = rest_default_additional_properties_to_false( $schema['items'] );
+		}
+	}
+
+	return $schema;
+}
diff --git a/wp-includes/rest-api/endpoints/class-wp-rest-themes-controller.php b/wp-includes/rest-api/endpoints/class-wp-rest-themes-controller.php
index f5aed07b64..62b83ba90b 100644
--- a/wp-includes/rest-api/endpoints/class-wp-rest-themes-controller.php
+++ b/wp-includes/rest-api/endpoints/class-wp-rest-themes-controller.php
@@ -167,50 +167,38 @@ class WP_REST_Themes_Controller extends WP_REST_Controller {
 		}
 
 		if ( rest_is_field_included( 'theme_supports', $fields ) ) {
-			$item_schemas   = $this->get_item_schema();
-			$theme_supports = $item_schemas['properties']['theme_supports']['properties'];
-			foreach ( $theme_supports as $name => $schema ) {
+			foreach ( get_registered_theme_features() as $feature => $config ) {
+				if ( ! is_array( $config['show_in_rest'] ) ) {
+					continue;
+				}
+
+				$name = $config['show_in_rest']['name'];
+
 				if ( ! rest_is_field_included( "theme_supports.{$name}", $fields ) ) {
 					continue;
 				}
 
-				if ( 'formats' === $name ) {
+				if ( ! current_theme_supports( $feature ) ) {
+					$data['theme_supports'][ $name ] = $config['show_in_rest']['schema']['default'];
 					continue;
 				}
 
-				if ( ! current_theme_supports( $name ) ) {
-					$data['theme_supports'][ $name ] = false;
+				$support = get_theme_support( $feature );
+
+				if ( isset( $config['show_in_rest']['prepare_callback'] ) ) {
+					$prepare = $config['show_in_rest']['prepare_callback'];
+				} else {
+					$prepare = array( $this, 'prepare_theme_support' );
+				}
+
+				$prepared = $prepare( $support, $config, $feature, $request );
+
+				if ( is_wp_error( $prepared ) ) {
 					continue;
 				}
 
-				if ( 'boolean' === $schema['type'] ) {
-					$data['theme_supports'][ $name ] = true;
-					continue;
-				}
-
-				$support = get_theme_support( $name );
-
-				if ( is_array( $support ) ) {
-					// None of the Core theme supports have variadic args.
-					$support = $support[0];
-
-					// Core multi-type theme-support schema definitions always list boolean first.
-					if ( is_array( $schema['type'] ) && 'boolean' === $schema['type'][0] ) {
-						// Pass the non-boolean type through to the sanitizer, which cannot itself
-						// determine the intended type if the value is invalid (for example if an
-						// object includes non-safelisted properties).
-						$schema['type'] = $schema['type'][1];
-					}
-				}
-
-				$data['theme_supports'][ $name ] = rest_sanitize_value_from_schema( $support, $schema );
+				$data['theme_supports'][ $name ] = $prepared;
 			}
-
-			$formats = get_theme_support( 'post-formats' );
-			$formats = is_array( $formats ) ? array_values( $formats[0] ) : array();
-			$formats = array_merge( array( 'standard' ), $formats );
-
-			$data['theme_supports']['formats'] = $formats;
 		}
 
 		$data = $this->add_additional_fields_to_object( $data, $request );
@@ -230,6 +218,41 @@ class WP_REST_Themes_Controller extends WP_REST_Controller {
 		return apply_filters( 'rest_prepare_theme', $response, $theme, $request );
 	}
 
+	/**
+	 * Prepares the theme support value for inclusion in the REST API response.
+	 *
+	 * @since 5.5.0
+	 *
+	 * @param mixed           $support The raw value from {@see get_theme_support()}
+	 * @param array           $args    The feature's registration args.
+	 * @param string          $feature The feature name.
+	 * @param WP_REST_Request $request The request object.
+	 * @return mixed The prepared support value.
+	 */
+	protected function prepare_theme_support( $support, $args, $feature, $request ) {
+		$schema = $args['show_in_rest']['schema'];
+
+		if ( 'boolean' === $schema['type'] ) {
+			return true;
+		}
+
+		if ( is_array( $support ) ) {
+			if ( ! $args['variadic'] ) {
+				$support = $support[0];
+			}
+
+			// Multi-type theme-support schema definitions always list boolean first.
+			if ( is_array( $schema['type'] ) && 'boolean' === $schema['type'][0] ) {
+				// Pass the non-boolean type through to the sanitizer, which cannot itself
+				// determine the intended type if the value is invalid (for example if an
+				// object includes non-safelisted properties). See #50300.
+				$schema['type'] = $schema['type'][1];
+			}
+		}
+
+		return rest_sanitize_value_from_schema( $support, $schema );
+	}
+
 	/**
 	 * Retrieves the theme's schema, conforming to JSON Schema.
 	 *
@@ -362,267 +385,7 @@ class WP_REST_Themes_Controller extends WP_REST_Controller {
 					'description' => __( 'Features supported by this theme.' ),
 					'type'        => 'object',
 					'readonly'    => true,
-					'properties'  => array(
-						'align-wide'                => array(
-							'description' => __( 'Whether theme opts in to wide alignment CSS class.' ),
-							'type'        => 'boolean',
-						),
-						'automatic-feed-links'      => array(
-							'description' => __( 'Whether posts and comments RSS feed links are added to head.' ),
-							'type'        => 'boolean',
-						),
-						'custom-header'             => array(
-							'description'          => __( 'Custom header if defined by the theme.' ),
-							'type'                 => array( 'boolean', 'object' ),
-							'properties'           => array(
-								'default-image'      => array(
-									'type'   => 'string',
-									'format' => 'uri',
-								),
-								'random-default'     => array(
-									'type' => 'boolean',
-								),
-								'width'              => array(
-									'type' => 'integer',
-								),
-								'height'             => array(
-									'type' => 'integer',
-								),
-								'flex-height'        => array(
-									'type' => 'boolean',
-								),
-								'flex-width'         => array(
-									'type' => 'boolean',
-								),
-								'default-text-color' => array(
-									'type' => 'string',
-								),
-								'header-text'        => array(
-									'type' => 'boolean',
-								),
-								'uploads'            => array(
-									'type' => 'boolean',
-								),
-								'video'              => array(
-									'type' => 'boolean',
-								),
-							),
-							'additionalProperties' => false,
-						),
-						'custom-background'         => array(
-							'description'          => __( 'Custom background if defined by the theme.' ),
-							'type'                 => array( 'boolean', 'object' ),
-							'properties'           => array(
-								'default-image'      => array(
-									'type'   => 'string',
-									'format' => 'uri',
-								),
-								'default-preset'     => array(
-									'type' => 'string',
-									'enum' => array(
-										'default',
-										'fill',
-										'fit',
-										'repeat',
-										'custom',
-									),
-								),
-								'default-position-x' => array(
-									'type' => 'string',
-									'enum' => array(
-										'left',
-										'center',
-										'right',
-									),
-								),
-								'default-position-y' => array(
-									'type' => 'string',
-									'enum' => array(
-										'left',
-										'center',
-										'right',
-									),
-								),
-								'default-size'       => array(
-									'type' => 'string',
-									'enum' => array(
-										'auto',
-										'contain',
-										'cover',
-									),
-								),
-								'default-repeat'     => array(
-									'type' => 'string',
-									'enum' => array(
-										'repeat-x',
-										'repeat-y',
-										'repeat',
-										'no-repeat',
-									),
-								),
-								'default-attachment' => array(
-									'type' => 'string',
-									'enum' => array(
-										'scroll',
-										'fixed',
-									),
-								),
-								'default-color'      => array(
-									'type' => 'string',
-								),
-							),
-							'additionalProperties' => false,
-						),
-						'custom-logo'               => array(
-							'description'          => __( 'Custom logo if defined by the theme.' ),
-							'type'                 => array( 'boolean', 'object' ),
-							'properties'           => array(
-								'width'       => array(
-									'type' => 'integer',
-								),
-								'height'      => array(
-									'type' => 'integer',
-								),
-								'flex-width'  => array(
-									'type' => 'boolean',
-								),
-								'flex-height' => array(
-									'type' => 'boolean',
-								),
-								'header-text' => array(
-									'type'  => 'array',
-									'items' => array(
-										'type' => 'string',
-									),
-								),
-							),
-							'additionalProperties' => false,
-						),
-						'customize-selective-refresh-widgets' => array(
-							'description' => __( 'Whether the theme enables Selective Refresh for Widgets being managed with the Customizer.' ),
-							'type'        => 'boolean',
-						),
-						'dark-editor-style'         => array(
-							'description' => __( 'Whether theme opts in to the dark editor style UI.' ),
-							'type'        => 'boolean',
-						),
-						'disable-custom-colors'     => array(
-							'description' => __( 'Whether the theme disables custom colors.' ),
-							'type'        => 'boolean',
-						),
-						'disable-custom-font-sizes' => array(
-							'description' => __( 'Whether the theme disables custom font sizes.' ),
-							'type'        => 'boolean',
-						),
-						'disable-custom-gradients'  => array(
-							'description' => __( 'Whether the theme disables custom gradients.' ),
-							'type'        => 'boolean',
-						),
-						'editor-color-palette'      => array(
-							'description' => __( 'Custom color palette if defined by the theme.' ),
-							'type'        => array( 'boolean', 'array' ),
-							'items'       => array(
-								'type'                 => 'object',
-								'properties'           => array(
-									'name'  => array(
-										'type' => 'string',
-									),
-									'slug'  => array(
-										'type' => 'string',
-									),
-									'color' => array(
-										'type' => 'string',
-									),
-								),
-								'additionalProperties' => false,
-							),
-						),
-						'editor-font-sizes'         => array(
-							'description' => __( 'Custom font sizes if defined by the theme.' ),
-							'type'        => array( 'boolean', 'array' ),
-							'items'       => array(
-								'type'                 => 'object',
-								'properties'           => array(
-									'name' => array(
-										'type' => 'string',
-									),
-									'size' => array(
-										'type' => 'number',
-									),
-									'slug' => array(
-										'type' => 'string',
-									),
-								),
-								'additionalProperties' => false,
-							),
-						),
-						'editor-gradient-presets'   => array(
-							'description' => __( 'Custom gradient presets if defined by the theme.' ),
-							'type'        => array( 'boolean', 'array' ),
-							'items'       => array(
-								'type'                 => 'object',
-								'properties'           => array(
-									'name'     => array(
-										'type' => 'string',
-									),
-									'gradient' => array(
-										'type' => 'string',
-									),
-									'slug'     => array(
-										'type' => 'string',
-									),
-								),
-								'additionalProperties' => false,
-							),
-						),
-						'editor-styles'             => array(
-							'description' => __( 'Whether theme opts in to the editor styles CSS wrapper.' ),
-							'type'        => 'boolean',
-						),
-						'formats'                   => array(
-							'description' => __( 'Post formats supported.' ),
-							'type'        => 'array',
-							'items'       => array(
-								'type' => 'string',
-								'enum' => get_post_format_slugs(),
-							),
-						),
-						'html5'                     => array(
-							'description' => __( 'Allows use of html5 markup for search forms, comment forms, comment lists, gallery, and caption.' ),
-							'type'        => array( 'boolean', 'array' ),
-							'items'       => array(
-								'type' => 'string',
-								'enum' => array(
-									'search-form',
-									'comment-form',
-									'comment-list',
-									'gallery',
-									'caption',
-									'script',
-									'style',
-								),
-							),
-						),
-						'post-thumbnails'           => array(
-							'description' => __( 'Whether the theme supports post thumbnails.' ),
-							'type'        => array( 'boolean', 'array' ),
-							'items'       => array(
-								'type' => 'string',
-							),
-						),
-						'responsive-embeds'         => array(
-							'description' => __( 'Whether the theme supports responsive embedded content.' ),
-							'type'        => 'boolean',
-						),
-						'title-tag'                 => array(
-							'description' => __( 'Whether the theme can manage the document title tag.' ),
-							'type'        => 'boolean',
-						),
-						'wp-block-styles'           => array(
-							'description' => __( 'Whether theme opts in to default WordPress block styles for viewing.' ),
-							'type'        => 'boolean',
-						),
-					),
+					'properties'  => array(),
 				),
 				'theme_uri'      => array(
 					'description' => __( 'The URI of the theme\'s webpage.' ),
@@ -649,6 +412,16 @@ class WP_REST_Themes_Controller extends WP_REST_Controller {
 			),
 		);
 
+		foreach ( get_registered_theme_features() as $feature => $config ) {
+			if ( ! is_array( $config['show_in_rest'] ) ) {
+				continue;
+			}
+
+			$name = $config['show_in_rest']['name'];
+
+			$schema['properties']['theme_supports']['properties'][ $name ] = $config['show_in_rest']['schema'];
+		}
+
 		$this->schema = $schema;
 
 		return $this->add_additional_fields_schema( $this->schema );
diff --git a/wp-includes/theme.php b/wp-includes/theme.php
index 80b0f1c072..baf1ea2157 100644
--- a/wp-includes/theme.php
+++ b/wp-includes/theme.php
@@ -2993,6 +2993,156 @@ function require_if_theme_supports( $feature, $include ) {
 	return false;
 }
 
+/**
+ * Registers a theme feature for use in {@see add_theme_support}.
+ *
+ * This does not indicate that the current theme supports the feature, it only describes the feature's supported options.
+ *
+ * @since 5.5.0
+ *
+ * @global $_wp_registered_theme_features
+ *
+ * @param string $feature The name uniquely identifying the feature.
+ * @param array $args {
+ *      Data used to describe the theme
+ *
+ *      @type string     $type         The type of data associated with this feature. Defaults to 'boolean'.
+ *                                     Valid values are 'string', 'boolean', 'integer', 'number', 'array', and 'object'.
+ *      @type boolean    $variadic     Does this feature utilize the variadic support of {@see add_theme_support()},
+ *                                     or are all arguments specified as the second parameter. Must be used with the "array" type.
+ *      @type string     $description  A short description of the feature. Included in the Themes REST API schema. Intended for developers.
+ *      @type bool|array $show_in_rest {
+ *          Whether this feature should be included in the Themes REST API endpoint. Defaults to not being included.
+ *          When registering an 'array' or 'object' type, this argument must be an array with the 'schema' key.
+ *
+ *          @type array    $schema           Specifies the JSON Schema definition describing the feature. If any objects in the schema
+ *                                           do not include the 'additionalProperties' keyword, it is set to false.
+ *          @type string   $name             An alternate name to be use as the property name in the REST API.
+ *          @type callable $prepare_callback A function used to format the theme support in the REST API. Receives the raw theme support value.
+ *      }
+ * }
+ * @return true|WP_Error True if the theme feature was successfully registered, a WP_Error object if not.
+ */
+function register_theme_feature( $feature, $args = array() ) {
+	global $_wp_registered_theme_features;
+
+	if ( ! is_array( $_wp_registered_theme_features ) ) {
+		$_wp_registered_theme_features = array();
+	}
+
+	$defaults = array(
+		'type'         => 'boolean',
+		'variadic'     => false,
+		'description'  => '',
+		'show_in_rest' => false,
+	);
+
+	$args = wp_parse_args( $args, $defaults );
+
+	if ( true === $args['show_in_rest'] ) {
+		$args['show_in_rest'] = array();
+	}
+
+	if ( is_array( $args['show_in_rest'] ) ) {
+		$args['show_in_rest'] = wp_parse_args(
+			$args['show_in_rest'],
+			array(
+				'schema'           => array(),
+				'name'             => $feature,
+				'prepare_callback' => null,
+			)
+		);
+	}
+
+	if ( ! in_array( $args['type'], array( 'string', 'boolean', 'integer', 'number', 'array', 'object' ), true ) ) {
+		return new WP_Error( 'invalid_type', __( 'The feature "type" is not valid JSON Schema type.' ) );
+	}
+
+	if ( true === $args['variadic'] && 'array' !== $args['type'] ) {
+		return new WP_Error( 'variadic_must_be_array', __( 'When registering a "variadic" theme feature, the "type" must be an "array".' ) );
+	}
+
+	if ( false !== $args['show_in_rest'] && in_array( $args['type'], array( 'array', 'object' ), true ) ) {
+		if ( ! is_array( $args['show_in_rest'] ) || empty( $args['show_in_rest']['schema'] ) ) {
+			return new WP_Error( 'missing_schema', __( 'When registering an "array" or "object" feature to show in the REST API, the feature\'s schema must also be defined.' ) );
+		}
+
+		if ( 'array' === $args['type'] && ! isset( $args['show_in_rest']['schema']['items'] ) ) {
+			return new WP_Error( 'missing_schema_items', __( 'When registering an "array" feature, the feature\'s schema must include the "items" keyword.' ) );
+		}
+
+		if ( 'object' === $args['type'] && ! isset( $args['show_in_rest']['schema']['properties'] ) ) {
+			return new WP_Error( 'missing_schema_properties', __( 'When registering an "object" feature, the feature\'s schema must include the "properties" keyword.' ) );
+		}
+	}
+
+	if ( is_array( $args['show_in_rest'] ) ) {
+		if ( isset( $args['show_in_rest']['prepare_callback'] ) && ! is_callable( $args['show_in_rest']['prepare_callback'] ) ) {
+			return new WP_Error( 'invalid_rest_prepare_callback', __( 'The prepare_callback must be a callable function.' ) );
+		}
+
+		$args['show_in_rest']['schema'] = wp_parse_args(
+			$args['show_in_rest']['schema'],
+			array(
+				'description' => $args['description'],
+				'type'        => $args['type'],
+				'default'     => false,
+			)
+		);
+
+		if ( is_bool( $args['show_in_rest']['schema']['default'] ) && ! in_array( 'boolean', (array) $args['show_in_rest']['schema']['type'], true ) ) {
+			// Automatically include the "boolean" type when the default value is a boolean.
+			$args['show_in_rest']['schema']['type'] = (array) $args['show_in_rest']['schema']['type'];
+			array_unshift( $args['show_in_rest']['schema']['type'], 'boolean' );
+		}
+
+		$args['show_in_rest']['schema'] = rest_default_additional_properties_to_false( $args['show_in_rest']['schema'] );
+	}
+
+	$_wp_registered_theme_features[ $feature ] = $args;
+
+	return true;
+}
+
+/**
+ * Gets the list of registered theme features.
+ *
+ * @since 5.5.0
+ *
+ * @global $_wp_registered_theme_features
+ *
+ * @return array[] List of theme features, keyed by their name.
+ */
+function get_registered_theme_features() {
+	global $_wp_registered_theme_features;
+
+	if ( ! is_array( $_wp_registered_theme_features ) ) {
+		return array();
+	}
+
+	return $_wp_registered_theme_features;
+}
+
+/**
+ * Gets the registration config for a theme feature.
+ *
+ * @since 5.5.0
+ *
+ * @global $_wp_registered_theme_features
+ *
+ * @param string $feature The feature name.
+ * @return array|null The registration args, or null if the feature was not registered.
+ */
+function get_registered_theme_feature( $feature ) {
+	global $_wp_registered_theme_features;
+
+	if ( ! is_array( $_wp_registered_theme_features ) ) {
+		return null;
+	}
+
+	return isset( $_wp_registered_theme_features[ $feature ] ) ? $_wp_registered_theme_features[ $feature ] : null;
+}
+
 /**
  * Checks an attachment being deleted to see if it's a header or background image.
  *
@@ -3462,3 +3612,371 @@ function _wp_keep_alive_customize_changeset_dependent_auto_drafts( $new_status,
 		clean_post_cache( $post_id );
 	}
 }
+
+/**
+ * Creates the initial theme features when the 'setup_theme' action is fired.
+ *
+ * See {@see 'setup_theme'}.
+ *
+ * @since 5.5.0
+ */
+function create_initial_theme_features() {
+	register_theme_feature(
+		'align-wide',
+		array(
+			'description'  => __( 'Whether theme opts in to wide alignment CSS class.' ),
+			'show_in_rest' => true,
+		)
+	);
+	register_theme_feature(
+		'automatic-feed-links',
+		array(
+			'description'  => __( 'Whether posts and comments RSS feed links are added to head.' ),
+			'show_in_rest' => true,
+		)
+	);
+	register_theme_feature(
+		'custom-background',
+		array(
+			'description'  => __( 'Custom background if defined by the theme.' ),
+			'type'         => 'object',
+			'show_in_rest' => array(
+				'schema' => array(
+					'properties' => array(
+						'default-image'      => array(
+							'type'   => 'string',
+							'format' => 'uri',
+						),
+						'default-preset'     => array(
+							'type' => 'string',
+							'enum' => array(
+								'default',
+								'fill',
+								'fit',
+								'repeat',
+								'custom',
+							),
+						),
+						'default-position-x' => array(
+							'type' => 'string',
+							'enum' => array(
+								'left',
+								'center',
+								'right',
+							),
+						),
+						'default-position-y' => array(
+							'type' => 'string',
+							'enum' => array(
+								'left',
+								'center',
+								'right',
+							),
+						),
+						'default-size'       => array(
+							'type' => 'string',
+							'enum' => array(
+								'auto',
+								'contain',
+								'cover',
+							),
+						),
+						'default-repeat'     => array(
+							'type' => 'string',
+							'enum' => array(
+								'repeat-x',
+								'repeat-y',
+								'repeat',
+								'no-repeat',
+							),
+						),
+						'default-attachment' => array(
+							'type' => 'string',
+							'enum' => array(
+								'scroll',
+								'fixed',
+							),
+						),
+						'default-color'      => array(
+							'type' => 'string',
+						),
+					),
+				),
+			),
+		)
+	);
+	register_theme_feature(
+		'custom-header',
+		array(
+			'description'  => __( 'Custom header if defined by the theme.' ),
+			'type'         => 'object',
+			'show_in_rest' => array(
+				'schema' => array(
+					'properties' => array(
+						'default-image'      => array(
+							'type'   => 'string',
+							'format' => 'uri',
+						),
+						'random-default'     => array(
+							'type' => 'boolean',
+						),
+						'width'              => array(
+							'type' => 'integer',
+						),
+						'height'             => array(
+							'type' => 'integer',
+						),
+						'flex-height'        => array(
+							'type' => 'boolean',
+						),
+						'flex-width'         => array(
+							'type' => 'boolean',
+						),
+						'default-text-color' => array(
+							'type' => 'string',
+						),
+						'header-text'        => array(
+							'type' => 'boolean',
+						),
+						'uploads'            => array(
+							'type' => 'boolean',
+						),
+						'video'              => array(
+							'type' => 'boolean',
+						),
+					),
+				),
+			),
+		)
+	);
+	register_theme_feature(
+		'custom-logo',
+		array(
+			'type'         => 'object',
+			'description'  => __( 'Custom logo if defined by the theme.' ),
+			'show_in_rest' => array(
+				'schema' => array(
+					'properties' => array(
+						'width'       => array(
+							'type' => 'integer',
+						),
+						'height'      => array(
+							'type' => 'integer',
+						),
+						'flex-width'  => array(
+							'type' => 'boolean',
+						),
+						'flex-height' => array(
+							'type' => 'boolean',
+						),
+						'header-text' => array(
+							'type'  => 'array',
+							'items' => array(
+								'type' => 'string',
+							),
+						),
+					),
+				),
+			),
+		)
+	);
+	register_theme_feature(
+		'customize-selective-refresh-widgets',
+		array(
+			'description'  => __( 'Whether the theme enables Selective Refresh for Widgets being managed with the Customizer.' ),
+			'show_in_rest' => true,
+		)
+	);
+	register_theme_feature(
+		'dark-editor-style',
+		array(
+			'description'  => __( 'Whether theme opts in to the dark editor style UI.' ),
+			'show_in_rest' => true,
+		)
+	);
+	register_theme_feature(
+		'disable-custom-colors',
+		array(
+			'description'  => __( 'Whether the theme disables custom colors.' ),
+			'show_in_rest' => true,
+		)
+	);
+	register_theme_feature(
+		'disable-custom-font-sizes',
+		array(
+			'description'  => __( 'Whether the theme disables custom font sizes.' ),
+			'show_in_rest' => true,
+		)
+	);
+	register_theme_feature(
+		'disable-custom-gradients',
+		array(
+			'description'  => __( 'Whether the theme disables custom gradients.' ),
+			'show_in_rest' => true,
+		)
+	);
+	register_theme_feature(
+		'editor-color-palette',
+		array(
+			'type'         => 'array',
+			'description'  => __( 'Custom color palette if defined by the theme.' ),
+			'show_in_rest' => array(
+				'schema' => array(
+					'items' => array(
+						'type'       => 'object',
+						'properties' => array(
+							'name'  => array(
+								'type' => 'string',
+							),
+							'slug'  => array(
+								'type' => 'string',
+							),
+							'color' => array(
+								'type' => 'string',
+							),
+						),
+					),
+				),
+			),
+		)
+	);
+	register_theme_feature(
+		'editor-font-sizes',
+		array(
+			'type'         => 'array',
+			'description'  => __( 'Custom font sizes if defined by the theme.' ),
+			'show_in_rest' => array(
+				'schema' => array(
+					'items' => array(
+						'type'       => 'object',
+						'properties' => array(
+							'name' => array(
+								'type' => 'string',
+							),
+							'size' => array(
+								'type' => 'number',
+							),
+							'slug' => array(
+								'type' => 'string',
+							),
+						),
+					),
+				),
+			),
+		)
+	);
+	register_theme_feature(
+		'editor-gradient-presets',
+		array(
+			'type'         => 'array',
+			'description'  => __( 'Custom gradient presets if defined by the theme.' ),
+			'show_in_rest' => array(
+				'schema' => array(
+					'items' => array(
+						'type'       => 'object',
+						'properties' => array(
+							'name'     => array(
+								'type' => 'string',
+							),
+							'gradient' => array(
+								'type' => 'string',
+							),
+							'slug'     => array(
+								'type' => 'string',
+							),
+						),
+					),
+				),
+			),
+		)
+	);
+	register_theme_feature(
+		'editor-styles',
+		array(
+			'description'  => __( 'Whether theme opts in to the editor styles CSS wrapper.' ),
+			'show_in_rest' => true,
+		)
+	);
+	register_theme_feature(
+		'html5',
+		array(
+			'type'         => 'array',
+			'description'  => __( 'Allows use of HTML5 markup for search forms, comment forms, comment lists, gallery, and caption.' ),
+			'show_in_rest' => array(
+				'schema' => array(
+					'items' => array(
+						'type' => 'string',
+						'enum' => array(
+							'search-form',
+							'comment-form',
+							'comment-list',
+							'gallery',
+							'caption',
+							'script',
+							'style',
+						),
+					),
+				),
+			),
+		)
+	);
+	register_theme_feature(
+		'post-formats',
+		array(
+			'type'         => 'array',
+			'description'  => __( 'Post formats supported.' ),
+			'show_in_rest' => array(
+				'name'             => 'formats',
+				'schema'           => array(
+					'items'   => array(
+						'type' => 'string',
+						'enum' => get_post_format_slugs(),
+					),
+					'default' => array( 'standard' ),
+				),
+				'prepare_callback' => static function ( $formats ) {
+					$formats = is_array( $formats ) ? array_values( $formats[0] ) : array();
+					$formats = array_merge( array( 'standard' ), $formats );
+
+					return $formats;
+				},
+			),
+		)
+	);
+	register_theme_feature(
+		'post-thumbnails',
+		array(
+			'type'         => 'array',
+			'description'  => __( 'The post types that support thumbnails or true if all post types are supported.' ),
+			'show_in_rest' => array(
+				'type'   => array( 'boolean', 'array' ),
+				'schema' => array(
+					'items' => array(
+						'type' => 'string',
+					),
+				),
+			),
+		)
+	);
+	register_theme_feature(
+		'responsive-embeds',
+		array(
+			'description'  => __( 'Whether the theme supports responsive embedded content.' ),
+			'show_in_rest' => true,
+		)
+	);
+	register_theme_feature(
+		'title-tag',
+		array(
+			'description'  => __( 'Whether the theme can manage the document title tag.' ),
+			'show_in_rest' => true,
+		)
+	);
+	register_theme_feature(
+		'wp-block-styles',
+		array(
+			'description'  => __( 'Whether theme opts in to default WordPress block styles for viewing.' ),
+			'show_in_rest' => true,
+		)
+	);
+}
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 3d38b306cc..477577b996 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.5-alpha-48170';
+$wp_version = '5.5-alpha-48171';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.