Editor: Add theme.json v3 migrations.

See https://github.com/WordPress/wordpress-develop/pull/6616.
See also the original Gutenberg PRs:
* https://github.com/WordPress/gutenberg/pull/58409
* https://github.com/WordPress/gutenberg/pull/61328
* https://github.com/WordPress/gutenberg/pull/61842
* https://github.com/WordPress/gutenberg/pull/62199
* https://github.com/WordPress/gutenberg/pull/62252

Fixes #61282.

Props ajlende, talldanwp, ramonopoly, ellatrix.


Built from https://develop.svn.wordpress.org/trunk@58328


git-svn-id: http://core.svn.wordpress.org/trunk@57785 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/block-editor.php

@@ -814,6 +814,7 @@ function get_block_editor_theme_styles() {
  * Returns the classic theme supports settings for block editor.
  *
  * @since 6.2.0
+ * @since 6.6.0 Add support for 'editor-spacing-sizes' theme support.
  *
  * @return array The classic theme supports settings.
  */
@@ -844,5 +845,10 @@ function get_classic_theme_supports_block_editor_settings() {
 		$theme_settings['gradients'] = $gradient_presets;
 	}
 
+	$spacing_sizes = current( (array) get_theme_support( 'editor-spacing-sizes' ) );
+	if ( false !== $spacing_sizes ) {
+		$theme_settings['spacingSizes'] = $spacing_sizes;
+	}
+
 	return $theme_settings;
 }

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

@@ -39,7 +39,7 @@ class WP_Theme_JSON_Data {
 	 * @param array  $data   Array following the theme.json specification.
 	 * @param string $origin The origin of the data: default, theme, user.
 	 */
-	public function __construct( $data = array(), $origin = 'theme' ) {
+	public function __construct( $data = array( 'version' => WP_Theme_JSON::LATEST_SCHEMA ), $origin = 'theme' ) {
 		$this->origin     = $origin;
 		$this->theme_json = new WP_Theme_JSON( $data, $this->origin );
 	}

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

@@ -220,6 +220,7 @@ class WP_Theme_JSON_Resolver {
 	 * @since 5.8.0
 	 * @since 5.9.0 Theme supports have been inlined and the `$theme_support_data` argument removed.
 	 * @since 6.0.0 Added an `$options` parameter to allow the theme data to be returned without theme supports.
+	 * @since 6.6.0 Add support for 'default-font-sizes' and 'default-spacing-sizes' theme supports.
 	 *
 	 * @param array $deprecated Deprecated. Not used.
 	 * @param array $options {
@@ -243,7 +244,7 @@ class WP_Theme_JSON_Resolver {
 				$theme_json_data = static::read_json_file( $theme_json_file );
 				$theme_json_data = static::translate( $theme_json_data, $wp_theme->get( 'TextDomain' ) );
 			} else {
-				$theme_json_data = array();
+				$theme_json_data = array( 'version' => WP_Theme_JSON::LATEST_SCHEMA );
 			}
 
 			/**
@@ -310,6 +311,32 @@ class WP_Theme_JSON_Resolver {
 			}
 			$theme_support_data['settings']['color']['defaultGradients'] = $default_gradients;
 
+			if ( ! isset( $theme_support_data['settings']['typography'] ) ) {
+				$theme_support_data['settings']['typography'] = array();
+			}
+			$default_font_sizes = false;
+			if ( current_theme_supports( 'default-font-sizes' ) ) {
+				$default_font_sizes = true;
+			}
+			if ( ! isset( $theme_support_data['settings']['typography']['fontSizes'] ) ) {
+				// If the theme does not have any font sizes, we still want to show the core one.
+				$default_font_sizes = true;
+			}
+			$theme_support_data['settings']['typography']['defaultFontSizes'] = $default_font_sizes;
+
+			if ( ! isset( $theme_support_data['settings']['spacing'] ) ) {
+				$theme_support_data['settings']['spacing'] = array();
+			}
+			$default_spacing_sizes = false;
+			if ( current_theme_supports( 'default-spacing-sizes' ) ) {
+				$default_spacing_sizes = true;
+			}
+			if ( ! isset( $theme_support_data['settings']['spacing']['spacingSizes'] ) ) {
+				// If the theme does not have any spacing sizes, we still want to show the core one.
+				$default_spacing_sizes = true;
+			}
+			$theme_support_data['settings']['spacing']['defaultSpacingSizes'] = $default_spacing_sizes;
+
 			if ( ! isset( $theme_support_data['settings']['shadow'] ) ) {
 				$theme_support_data['settings']['shadow'] = array();
 			}
@@ -359,7 +386,7 @@ class WP_Theme_JSON_Resolver {
 			return static::$blocks;
 		}
 
-		$config = array( 'version' => 2 );
+		$config = array( 'version' => WP_Theme_JSON::LATEST_SCHEMA );
 		foreach ( $blocks as $block_name => $block_type ) {
 			if ( isset( $block_type->supports['__experimentalStyle'] ) ) {
 				$config['styles']['blocks'][ $block_name ] = static::remove_json_comments( $block_type->supports['__experimentalStyle'] );
@@ -494,6 +521,7 @@ class WP_Theme_JSON_Resolver {
 	 * Returns the user's origin config.
 	 *
 	 * @since 5.9.0
+	 * @since 6.6.0 The 'isGlobalStylesUserThemeJSON' flag is left on the user data.
 	 *
 	 * @return WP_Theme_JSON Entity that holds styles for user data.
 	 */
@@ -531,14 +559,18 @@ class WP_Theme_JSON_Resolver {
 				isset( $decoded_data['isGlobalStylesUserThemeJSON'] ) &&
 				$decoded_data['isGlobalStylesUserThemeJSON']
 			) {
-				unset( $decoded_data['isGlobalStylesUserThemeJSON'] );
 				$config = $decoded_data;
 			}
 		}
 
 		/** This filter is documented in wp-includes/class-wp-theme-json-resolver.php */
-		$theme_json   = apply_filters( 'wp_theme_json_data_user', new WP_Theme_JSON_Data( $config, 'custom' ) );
+		$theme_json = apply_filters( 'wp_theme_json_data_user', new WP_Theme_JSON_Data( $config, 'custom' ) );
-		static::$user = $theme_json->get_theme_json();
+		$config     = $theme_json->get_data();
+
+		// Needs to be set for schema migrations of user data.
+		$config['isGlobalStylesUserThemeJSON'] = true;
+
+		static::$user = new WP_Theme_JSON( $config, 'custom' );
 
 		return static::$user;
 	}
@@ -586,7 +618,6 @@ class WP_Theme_JSON_Resolver {
 		$result = new WP_Theme_JSON();
 		$result->merge( static::get_core_data() );
 		if ( 'default' === $origin ) {
-			$result->set_spacing_sizes();
 			return $result;
 		}
 
@@ -597,12 +628,10 @@ class WP_Theme_JSON_Resolver {
 
 		$result->merge( static::get_theme_data() );
 		if ( 'theme' === $origin ) {
-			$result->set_spacing_sizes();
 			return $result;
 		}
 
 		$result->merge( static::get_user_data() );
-		$result->set_spacing_sizes();
 
 		return $result;
 	}

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

@@ -35,6 +35,7 @@ class WP_Theme_JSON_Schema {
 	 * Function that migrates a given theme.json structure to the last version.
 	 *
 	 * @since 5.9.0
+	 * @since 6.6.0 Migrate up to v3.
 	 *
 	 * @param array $theme_json The structure to migrate.
 	 *
@@ -47,8 +48,14 @@ class WP_Theme_JSON_Schema {
 			);
 		}
 
-		if ( 1 === $theme_json['version'] ) {
+		// Migrate each version in order starting with the current version.
-			$theme_json = self::migrate_v1_to_v2( $theme_json );
+		switch ( $theme_json['version'] ) {
+			case 1:
+				$theme_json = self::migrate_v1_to_v2( $theme_json );
+				// no break
+			case 2:
+				$theme_json = self::migrate_v2_to_v3( $theme_json );
+				// no break
 		}
 
 		return $theme_json;
@@ -84,6 +91,88 @@ class WP_Theme_JSON_Schema {
 		return $new;
 	}
 
+	/**
+	 * Migrates from v2 to v3.
+	 *
+	 * - Sets settings.typography.defaultFontSizes to false.
+	 *
+	 * @since 6.6.0
+	 *
+	 * @param array $old Data to migrate.
+	 *
+	 * @return array Data with defaultFontSizes set to false.
+	 */
+	private static function migrate_v2_to_v3( $old ) {
+		// Copy everything.
+		$new = $old;
+
+		// Set the new version.
+		$new['version'] = 3;
+
+		/*
+		 * Remaining changes do not need to be applied to the custom origin,
+		 * as they should take on the value of the theme origin.
+		 */
+		if (
+			isset( $new['isGlobalStylesUserThemeJSON'] ) &&
+			true === $new['isGlobalStylesUserThemeJSON']
+		) {
+			return $new;
+		}
+
+		/*
+		 * Even though defaultFontSizes and defaultSpacingSizes are new
+		 * settings, we need to migrate them as they each control
+		 * PRESETS_METADATA prevent_override values which were previously
+		 * hardcoded to false. This only needs to happen when the theme provides
+		 * fontSizes or spacingSizes as they could match the default ones and
+		 * affect the generated CSS.
+		 */
+		if ( isset( $old['settings']['typography']['fontSizes'] ) ) {
+			if ( ! isset( $new['settings'] ) ) {
+				$new['settings'] = array();
+			}
+			if ( ! isset( $new['settings']['typography'] ) ) {
+				$new['settings']['typography'] = array();
+			}
+			$new['settings']['typography']['defaultFontSizes'] = false;
+		}
+
+		/*
+		 * Similarly to defaultFontSizes, we need to migrate defaultSpacingSizes
+		 * as it controls the PRESETS_METADATA prevent_override which was
+		 * previously hardcoded to false. This only needs to happen when the
+		 * theme provided spacing sizes via spacingSizes or spacingScale.
+		 */
+		if (
+			isset( $old['settings']['spacing']['spacingSizes'] ) ||
+			isset( $old['settings']['spacing']['spacingScale'] )
+		) {
+			if ( ! isset( $new['settings'] ) ) {
+				$new['settings'] = array();
+			}
+			if ( ! isset( $new['settings']['spacing'] ) ) {
+				$new['settings']['spacing'] = array();
+			}
+			$new['settings']['spacing']['defaultSpacingSizes'] = false;
+		}
+
+		/*
+		 * In v3 spacingSizes is merged with the generated spacingScale sizes
+		 * instead of completely replacing them. The v3 behavior is what was
+		 * documented for the v2 schema, but the code never actually did work
+		 * that way. Instead of surprising users with a behavior change two
+		 * years after the fact at the same time as a v3 update is introduced,
+		 * we'll continue using the "bugged" behavior for v2 themes. And treat
+		 * the "bug fix" as a breaking change for v3.
+		 */
+		if ( isset( $old['settings']['spacing']['spacingSizes'] ) ) {
+			unset( $new['settings']['spacing']['spacingScale'] );
+		}
+
+		return $new;
+	}
+
 	/**
 	 * Processes the settings subtree.
 	 *

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

@@ -123,7 +123,9 @@ class WP_Theme_JSON {
 	 *              `prevent_override` value for `color.duotone` to use `color.defaultDuotone`.
 	 * @since 6.2.0 Added 'shadow' presets.
 	 * @since 6.3.0 Replaced value_func for duotone with `null`. Custom properties are handled by class-wp-duotone.php.
-	 * @since 6.6.0 Added the `dimensions.aspectRatios` & `dimensions.defaultAspectRatios` preset.
+	 * @since 6.6.0 Added the `dimensions.aspectRatios` and `dimensions.defaultAspectRatios` presets.
+	 *              Updated the 'prevent_override' value for font size presets to use 'typography.defaultFontSizes'
+	 *              and spacing size presets to use `spacing.defaultSpacingSizes`.
 	 * @var array
 	 */
 	const PRESETS_METADATA = array(
@@ -169,7 +171,7 @@ class WP_Theme_JSON {
 		),
 		array(
 			'path'              => array( 'typography', 'fontSizes' ),
-			'prevent_override'  => false,
+			'prevent_override'  => array( 'typography', 'defaultFontSizes' ),
 			'use_default_names' => true,
 			'value_func'        => 'wp_get_typography_font_size_value',
 			'css_vars'          => '--wp--preset--font-size--$slug',
@@ -187,7 +189,7 @@ class WP_Theme_JSON {
 		),
 		array(
 			'path'              => array( 'spacing', 'spacingSizes' ),
-			'prevent_override'  => false,
+			'prevent_override'  => array( 'spacing', 'defaultSpacingSizes' ),
 			'use_default_names' => true,
 			'value_key'         => 'size',
 			'css_vars'          => '--wp--preset--spacing--$slug',
@@ -378,7 +380,8 @@ class WP_Theme_JSON {
 	 *              `typography.writingMode`, `lightbox.enabled` and `lightbox.allowEditing`.
 	 * @since 6.5.0 Added support for `layout.allowCustomContentAndWideSize`,
 	 *              `background.backgroundSize` and `dimensions.aspectRatio`.
-	 * @since 6.6.0 Added support for `dimensions.aspectRatios` and `dimensions.defaultAspectRatios`.
+	 * @since 6.6.0 Added support for 'dimensions.aspectRatios', 'dimensions.defaultAspectRatios',
+	 *              'typography.defaultFontSizes', and 'spacing.defaultSpacingSizes'.
 	 * @var array
 	 */
 	const VALID_SETTINGS = array(
@@ -433,33 +436,35 @@ class WP_Theme_JSON {
 			'sticky' => null,
 		),
 		'spacing'                       => array(
-			'customSpacingSize' => null,
+			'customSpacingSize'   => null,
-			'spacingSizes'      => null,
+			'defaultSpacingSizes' => null,
-			'spacingScale'      => null,
+			'spacingSizes'        => null,
-			'blockGap'          => null,
+			'spacingScale'        => null,
-			'margin'            => null,
+			'blockGap'            => null,
-			'padding'           => null,
+			'margin'              => null,
-			'units'             => null,
+			'padding'             => null,
+			'units'               => null,
 		),
 		'shadow'                        => array(
 			'presets'        => null,
 			'defaultPresets' => null,
 		),
 		'typography'                    => array(
-			'fluid'          => null,
+			'fluid'            => null,
-			'customFontSize' => null,
+			'customFontSize'   => null,
-			'dropCap'        => null,
+			'defaultFontSizes' => null,
-			'fontFamilies'   => null,
+			'dropCap'          => null,
-			'fontSizes'      => null,
+			'fontFamilies'     => null,
-			'fontStyle'      => null,
+			'fontSizes'        => null,
-			'fontWeight'     => null,
+			'fontStyle'        => null,
-			'letterSpacing'  => null,
+			'fontWeight'       => null,
-			'lineHeight'     => null,
+			'letterSpacing'    => null,
-			'textAlign'      => null,
+			'lineHeight'       => null,
-			'textColumns'    => null,
+			'textAlign'        => null,
-			'textDecoration' => null,
+			'textColumns'      => null,
-			'textTransform'  => null,
+			'textDecoration'   => null,
-			'writingMode'    => null,
+			'textTransform'    => null,
+			'writingMode'      => null,
 		),
 	);
 
@@ -728,20 +733,23 @@ class WP_Theme_JSON {
 	 *
 	 * @since 5.8.0
 	 * @since 5.9.0 Changed value from 1 to 2.
+	 * @since 6.6.0 Changed value from 2 to 3.
 	 * @var int
 	 */
-	const LATEST_SCHEMA = 2;
+	const LATEST_SCHEMA = 3;
 
 	/**
 	 * Constructor.
 	 *
 	 * @since 5.8.0
+	 * @since 6.6.0 Key spacingScale by origin, and Pre-generate the
+	 *              spacingSizes from spacingScale.
 	 *
 	 * @param array  $theme_json A structure that follows the theme.json schema.
 	 * @param string $origin     Optional. What source of data this object represents.
 	 *                           One of 'default', 'theme', or 'custom'. Default 'theme'.
 	 */
-	public function __construct( $theme_json = array(), $origin = 'theme' ) {
+	public function __construct( $theme_json = array( 'version' => WP_Theme_JSON::LATEST_SCHEMA ), $origin = 'theme' ) {
 		if ( ! in_array( $origin, static::VALID_ORIGINS, true ) ) {
 			$origin = 'theme';
 		}
@@ -750,8 +758,8 @@ class WP_Theme_JSON {
 		$valid_block_names   = array_keys( static::get_blocks_metadata() );
 		$valid_element_names = array_keys( static::ELEMENTS );
 		$valid_variations    = static::get_valid_block_style_variations();
-		$theme_json          = static::sanitize( $this->theme_json, $valid_block_names, $valid_element_names, $valid_variations );
+		$this->theme_json    = static::sanitize( $this->theme_json, $valid_block_names, $valid_element_names, $valid_variations );
-		$this->theme_json    = static::maybe_opt_in_into_settings( $theme_json );
+		$this->theme_json    = static::maybe_opt_in_into_settings( $this->theme_json );
 
 		// Internally, presets are keyed by origin.
 		$nodes = static::get_setting_nodes( $this->theme_json );
@@ -770,6 +778,27 @@ class WP_Theme_JSON {
 				}
 			}
 		}
+
+		// In addition to presets, spacingScale (which generates presets) is also keyed by origin.
+		$scale_path    = array( 'settings', 'spacing', 'spacingScale' );
+		$spacing_scale = _wp_array_get( $this->theme_json, $scale_path, null );
+		if ( null !== $spacing_scale ) {
+			// If the spacingScale is not already keyed by origin.
+			if ( empty( array_intersect( array_keys( $spacing_scale ), static::VALID_ORIGINS ) ) ) {
+				_wp_array_set( $this->theme_json, $scale_path, array( $origin => $spacing_scale ) );
+			}
+		}
+
+		// Pre-generate the spacingSizes from spacingScale.
+		$scale_path    = array( 'settings', 'spacing', 'spacingScale', $origin );
+		$spacing_scale = _wp_array_get( $this->theme_json, $scale_path, null );
+		if ( isset( $spacing_scale ) ) {
+			$sizes_path           = array( 'settings', 'spacing', 'spacingSizes', $origin );
+			$spacing_sizes        = _wp_array_get( $this->theme_json, $sizes_path, array() );
+			$spacing_scale_sizes  = static::compute_spacing_sizes( $spacing_scale );
+			$merged_spacing_sizes = static::merge_spacing_sizes( $spacing_scale_sizes, $spacing_sizes );
+			_wp_array_set( $this->theme_json, $sizes_path, $merged_spacing_sizes );
+		}
 	}
 
 	/**
@@ -2915,6 +2944,40 @@ class WP_Theme_JSON {
 		$incoming_data    = $incoming->get_raw_data();
 		$this->theme_json = array_replace_recursive( $this->theme_json, $incoming_data );
 
+		/*
+		 * Recompute all the spacing sizes based on the new hierarchy of data. In the constructor
+		 * spacingScale and spacingSizes are both keyed by origin and VALID_ORIGINS is ordered, so
+		 * we can allow partial spacingScale data to inherit missing data from earlier layers when
+		 * computing the spacing sizes.
+		 *
+		 * This happens before the presets are merged to ensure that default spacing sizes can be
+		 * removed from the theme origin if $prevent_override is true.
+		 */
+		$flattened_spacing_scale = array();
+		foreach ( static::VALID_ORIGINS as $origin ) {
+			$scale_path = array( 'settings', 'spacing', 'spacingScale', $origin );
+
+			// Apply the base spacing scale to the current layer.
+			$base_spacing_scale      = _wp_array_get( $this->theme_json, $scale_path, array() );
+			$flattened_spacing_scale = array_replace( $flattened_spacing_scale, $base_spacing_scale );
+
+			$spacing_scale = _wp_array_get( $incoming_data, $scale_path, null );
+			if ( ! isset( $spacing_scale ) ) {
+				continue;
+			}
+
+			// Allow partial scale settings by merging with lower layers.
+			$flattened_spacing_scale = array_replace( $flattened_spacing_scale, $spacing_scale );
+
+			// Generate and merge the scales for this layer.
+			$sizes_path           = array( 'settings', 'spacing', 'spacingSizes', $origin );
+			$spacing_sizes        = _wp_array_get( $incoming_data, $sizes_path, array() );
+			$spacing_scale_sizes  = static::compute_spacing_sizes( $flattened_spacing_scale );
+			$merged_spacing_sizes = static::merge_spacing_sizes( $spacing_scale_sizes, $spacing_sizes );
+
+			_wp_array_set( $incoming_data, $sizes_path, $merged_spacing_sizes );
+		}
+
 		/*
 		 * The array_replace_recursive algorithm merges at the leaf level,
 		 * but we don't want leaf arrays to be merged, so we overwrite it.
@@ -2951,12 +3014,15 @@ class WP_Theme_JSON {
 			}
 
 			// Replace the presets.
-			foreach ( static::PRESETS_METADATA as $preset ) {
+			foreach ( static::PRESETS_METADATA as $preset_metadata ) {
-				$override_preset = ! static::get_metadata_boolean( $this->theme_json['settings'], $preset['prevent_override'], true );
+				$prevent_override = $preset_metadata['prevent_override'];
+				if ( is_array( $prevent_override ) ) {
+					$prevent_override = _wp_array_get( $this->theme_json['settings'], $preset_metadata['prevent_override'] );
+				}
 
 				foreach ( static::VALID_ORIGINS as $origin ) {
 					$base_path = $node['path'];
-					foreach ( $preset['path'] as $leaf ) {
+					foreach ( $preset_metadata['path'] as $leaf ) {
 						$base_path[] = $leaf;
 					}
 
@@ -2968,7 +3034,8 @@ class WP_Theme_JSON {
 						continue;
 					}
 
-					if ( 'theme' === $origin && $preset['use_default_names'] ) {
+					// Set names for theme presets based on the slug if they are not set and can use default names.
+					if ( 'theme' === $origin && $preset_metadata['use_default_names'] ) {
 						foreach ( $content as $key => $item ) {
 							if ( ! isset( $item['name'] ) ) {
 								$name = static::get_name_from_defaults( $item['slug'], $base_path );
@@ -2979,19 +3046,17 @@ class WP_Theme_JSON {
 						}
 					}
 
-					if (
+					// Filter out default slugs from theme presets when defaults should not be overridden.
-						( 'theme' !== $origin ) ||
+					if ( 'theme' === $origin && $prevent_override ) {
-						( 'theme' === $origin && $override_preset )
+						$slugs_node    = static::get_default_slugs( $this->theme_json, $node['path'] );
-					) {
+						$preset_global = _wp_array_get( $slugs_global, $preset_metadata['path'], array() );
-						_wp_array_set( $this->theme_json, $path, $content );
+						$preset_node   = _wp_array_get( $slugs_node, $preset_metadata['path'], array() );
-					} else {
+						$preset_slugs  = array_merge_recursive( $preset_global, $preset_node );
-						$slugs_node = static::get_default_slugs( $this->theme_json, $node['path'] );
-						$slugs      = array_merge_recursive( $slugs_global, $slugs_node );
 
-						$slugs_for_preset = _wp_array_get( $slugs, $preset['path'], array() );
+						$content = static::filter_slugs( $content, $preset_slugs );
-						$content          = static::filter_slugs( $content, $slugs_for_preset );
-						_wp_array_set( $this->theme_json, $path, $content );
 					}
+
+					_wp_array_set( $this->theme_json, $path, $content );
 				}
 			}
 		}
@@ -3530,6 +3595,13 @@ class WP_Theme_JSON {
 			$theme_settings['settings']['spacing']['padding'] = $settings['enableCustomSpacing'];
 		}
 
+		if ( isset( $settings['spacingSizes'] ) ) {
+			if ( ! isset( $theme_settings['settings']['spacing'] ) ) {
+				$theme_settings['settings']['spacing'] = array();
+			}
+			$theme_settings['settings']['spacing']['spacingSizes'] = $settings['spacingSizes'];
+		}
+
 		return $theme_settings;
 	}
 
@@ -3703,10 +3775,16 @@ class WP_Theme_JSON {
 	 * Sets the spacingSizes array based on the spacingScale values from theme.json.
 	 *
 	 * @since 6.1.0
+	 * @deprecated 6.6.0
+	 *
+	 * @param string $origin Optional. What source of data to set the spacing sizes for.
+	 *                       One of 'default', 'theme', or 'custom'. Default 'default'.
 	 *
 	 * @return null|void
 	 */
 	public function set_spacing_sizes() {
+		_deprecated_function( __METHOD__, '6.6.0' );
+
 		$spacing_scale = isset( $this->theme_json['settings']['spacing']['spacingScale'] )
 			? $this->theme_json['settings']['spacing']['spacingScale']
 			: array();
@@ -3740,6 +3818,99 @@ class WP_Theme_JSON {
 			return null;
 		}
 
+		$spacing_sizes = static::compute_spacing_sizes( $spacing_scale );
+
+		// If there are 7 or fewer steps in the scale revert to numbers for labels instead of t-shirt sizes.
+		if ( $spacing_scale['steps'] <= 7 ) {
+			for ( $spacing_sizes_count = 0; $spacing_sizes_count < count( $spacing_sizes ); $spacing_sizes_count++ ) {
+				$spacing_sizes[ $spacing_sizes_count ]['name'] = (string) ( $spacing_sizes_count + 1 );
+			}
+		}
+
+		_wp_array_set( $this->theme_json, array( 'settings', 'spacing', 'spacingSizes', 'default' ), $spacing_sizes );
+	}
+
+	/**
+	 * Merges two sets of spacing size presets.
+	 *
+	 * @since 6.6.0
+	 *
+	 * @param array $base     The base set of spacing sizes.
+	 * @param array $incoming The set of spacing sizes to merge with the base. Duplicate slugs will override the base values.
+	 * @return array The merged set of spacing sizes.
+	 */
+	private static function merge_spacing_sizes( $base, $incoming ) {
+		// Preserve the order if there are no base (spacingScale) values.
+		if ( empty( $base ) ) {
+			return $incoming;
+		}
+		$merged = array();
+		foreach ( $base as $item ) {
+			$merged[ $item['slug'] ] = $item;
+		}
+		foreach ( $incoming as $item ) {
+			$merged[ $item['slug'] ] = $item;
+		}
+		ksort( $merged, SORT_NUMERIC );
+		return array_values( $merged );
+	}
+
+	/**
+	 * Generates a set of spacing sizes by starting with a medium size and
+	 * applying an operator with an increment value to generate the rest of the
+	 * sizes outward from the medium size. The medium slug is '50' with the rest
+	 * of the slugs being 10 apart. The generated names use t-shirt sizing.
+	 *
+	 * Example:
+	 *
+	 *     $spacing_scale = array(
+	 *         'steps'      => 4,
+	 *         'mediumStep' => 16,
+	 *         'unit'       => 'px',
+	 *         'operator'   => '+',
+	 *         'increment'  => 2,
+	 *     );
+	 *     $spacing_sizes = static::compute_spacing_sizes( $spacing_scale );
+	 *     // -> array(
+	 *     //        array( 'name' => 'Small',   'slug' => '40', 'size' => '14px' ),
+	 *     //        array( 'name' => 'Medium',  'slug' => '50', 'size' => '16px' ),
+	 *     //        array( 'name' => 'Large',   'slug' => '60', 'size' => '18px' ),
+	 *     //        array( 'name' => 'X-Large', 'slug' => '70', 'size' => '20px' ),
+	 *     //    )
+	 *
+	 * @since 6.6.0
+	 *
+	 * @param array $spacing_scale {
+	 *      The spacing scale values. All are required.
+	 *
+	 *      @type int    $steps      The number of steps in the scale. (up to 10 steps are supported.)
+	 *      @type float  $mediumStep The middle value that gets the slug '50'. (For even number of steps, this becomes the first middle value.)
+	 *      @type string $unit       The CSS unit to use for the sizes.
+	 *      @type string $operator   The mathematical operator to apply to generate the other sizes. Either '+' or '*'.
+	 *      @type float  $increment  The value used with the operator to generate the other sizes.
+	 * }
+	 * @return array The spacing sizes presets or an empty array if some spacing scale values are missing or invalid.
+	 */
+	private static function compute_spacing_sizes( $spacing_scale ) {
+		/*
+		 * This condition is intentionally missing some checks on ranges for the values in order to
+		 * keep backwards compatibility with the previous implementation.
+		 */
+		if (
+			! isset( $spacing_scale['steps'] ) ||
+			! is_numeric( $spacing_scale['steps'] ) ||
+			0 === $spacing_scale['steps'] ||
+			! isset( $spacing_scale['mediumStep'] ) ||
+			! is_numeric( $spacing_scale['mediumStep'] ) ||
+			! isset( $spacing_scale['unit'] ) ||
+			! isset( $spacing_scale['operator'] ) ||
+			( '+' !== $spacing_scale['operator'] && '*' !== $spacing_scale['operator'] ) ||
+			! isset( $spacing_scale['increment'] ) ||
+			! is_numeric( $spacing_scale['increment'] )
+		) {
+			return array();
+		}
+
 		$unit            = '%' === $spacing_scale['unit'] ? '%' : sanitize_title( $spacing_scale['unit'] );
 		$current_step    = $spacing_scale['mediumStep'];
 		$steps_mid_point = round( $spacing_scale['steps'] / 2, 0 );
@@ -3822,14 +3993,7 @@ class WP_Theme_JSON {
 			$spacing_sizes[] = $above_sizes_item;
 		}
 
-		// If there are 7 or fewer steps in the scale revert to numbers for labels instead of t-shirt sizes.
+		return $spacing_sizes;
-		if ( $spacing_scale['steps'] <= 7 ) {
-			for ( $spacing_sizes_count = 0; $spacing_sizes_count < count( $spacing_sizes ); $spacing_sizes_count++ ) {
-				$spacing_sizes[ $spacing_sizes_count ]['name'] = (string) ( $spacing_sizes_count + 1 );
-			}
-		}
-
-		_wp_array_set( $this->theme_json, array( 'settings', 'spacing', 'spacingSizes', 'default' ), $spacing_sizes );
 	}
 
 	/**

wp-includes/rest-api/endpoints/class-wp-rest-font-faces-controller.php

@@ -18,7 +18,7 @@ class WP_REST_Font_Faces_Controller extends WP_REST_Posts_Controller {
 	 * @since 6.5.0
 	 * @var int
 	 */
-	const LATEST_THEME_JSON_VERSION_SUPPORTED = 2;
+	const LATEST_THEME_JSON_VERSION_SUPPORTED = 3;
 
 	/**
 	 * Whether the controller supports batching.

wp-includes/rest-api/endpoints/class-wp-rest-font-families-controller.php

@@ -20,7 +20,7 @@ class WP_REST_Font_Families_Controller extends WP_REST_Posts_Controller {
 	 * @since 6.5.0
 	 * @var int
 	 */
-	const LATEST_THEME_JSON_VERSION_SUPPORTED = 2;
+	const LATEST_THEME_JSON_VERSION_SUPPORTED = 3;
 
 	/**
 	 * Whether the controller supports batching.

wp-includes/theme.json

@@ -1,6 +1,6 @@
 {
 	"$schema": "https://schemas.wp.org/trunk/theme.json",
-	"version": 2,
+	"version": 3,
 	"settings": {
 		"appearanceTools": false,
 		"useRootPaddingAwareAlignments": false,
@@ -265,6 +265,7 @@
 			"margin": false,
 			"padding": false,
 			"customSpacingSize": true,
+			"defaultSpacingSizes": true,
 			"units": [ "px", "em", "rem", "vh", "vw", "%" ],
 			"spacingScale": {
 				"operator": "*",
@@ -276,6 +277,7 @@
 		},
 		"typography": {
 			"customFontSize": true,
+			"defaultFontSizes": true,
 			"dropCap": true,
 			"fontSizes": [
 				{

wp-includes/theme.php

@@ -2642,6 +2642,7 @@ function get_theme_starter_content() {
  * @since 6.3.0 The `border` feature allows themes without theme.json to add border styles to blocks.
  * @since 6.5.0 The `appearance-tools` feature enables a few design tools for blocks,
  *              see `WP_Theme_JSON::APPEARANCE_TOOLS_OPT_INS` for a complete list.
+ * @since 6.6.0 The `editor-spacing-sizes` feature was added.
  *
  * @global array $_wp_theme_features
  *
@@ -2669,6 +2670,7 @@ function get_theme_starter_content() {
  *                          - 'editor-color-palette'
  *                          - 'editor-gradient-presets'
  *                          - 'editor-font-sizes'
+ *                          - 'editor-spacing-sizes'
  *                          - 'editor-styles'
  *                          - 'featured-content'
  *                          - 'html5'
@@ -4226,6 +4228,31 @@ function create_initial_theme_features() {
 			),
 		)
 	);
+	register_theme_feature(
+		'editor-spacing-sizes',
+		array(
+			'type'         => 'array',
+			'description'  => __( 'Custom spacing 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' => 'string',
+							),
+							'slug' => array(
+								'type' => 'string',
+							),
+						),
+					),
+				),
+			),
+		)
+	);
 	register_theme_feature(
 		'editor-styles',
 		array(

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.6-alpha-58327';
+$wp_version = '6.6-alpha-58328';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.