Editor: Backport foundation for Layout block support refactor (part 1).

This change backports the following changes from Gutenberg repository:

- [WordPress/gutenberg#40875 gutenberg#40875] Layout: Use semantic classnames, centralize layout definitions, reduce duplication, and fix blockGap in theme.json
- [WordPress/gutenberg#42544 gutenberg#42544] Layout: Add a disable-layout-styles theme supports flag to opt out of all layout styles gutenberg#42544
- [WordPress/gutenberg#42087 gutenberg#42087] Theme.json: Add block support feature level selectors for blocks gutenberg#42087
- [WordPress/gutenberg#43792 gutenberg#43792] Global Styles: Split root layout rules into a different function gutenberg#43792
- [WordPress/gutenberg#42544 gutenberg#42544] Layout: Add a disable-layout-styles theme supports flag to opt out of all layout styles gutenberg#42544
- [WordPress/gutenberg#42665 gutenberg#42665] Layout: Reduce specificity of fallback blockGap styles gutenberg#42665
- [WordPress/gutenberg#42085 gutenberg#42085] Core CSS support for root padding and alignfull blocks gutenberg#42085

Note that it doesn't entirely port over PR40875 — the remaining PHP changes for that PR will be explored in a separate PR targeting `layout.php`.

Props andrewserong, aaronrobertshaw, isabel_brison.
See #56467.

Built from https://develop.svn.wordpress.org/trunk@54159

wp-includes/block-editor.php

@@ -209,6 +209,7 @@ function get_default_block_editor_settings() {
 		'disableCustomColors'              => get_theme_support( 'disable-custom-colors' ),
 		'disableCustomFontSizes'           => get_theme_support( 'disable-custom-font-sizes' ),
 		'disableCustomGradients'           => get_theme_support( 'disable-custom-gradients' ),
+		'disableLayoutStyles'              => get_theme_support( 'disable-layout-styles' ),
 		'enableCustomLineHeight'           => get_theme_support( 'custom-line-height' ),
 		'enableCustomSpacing'              => get_theme_support( 'custom-spacing' ),
 		'enableCustomUnits'                => get_theme_support( 'custom-units' ),
@@ -417,6 +418,18 @@ function get_block_editor_settings( array $custom_settings, $block_editor_contex
 			$block_classes['css'] = $actual_css;
 			$global_styles[]      = $block_classes;
 		}
+	} else {
+		// If there is no `theme.json` file, ensure base layout styles are still available.
+		$block_classes = array(
+			'css'            => 'base-layout-styles',
+			'__unstableType' => 'base-layout',
+			'isGlobalStyles' => true,
+		);
+		$actual_css    = wp_get_global_stylesheet( array( $block_classes['css'] ) );
+		if ( '' !== $actual_css ) {
+			$block_classes['css'] = $actual_css;
+			$global_styles[]  = $block_classes;
+		}
 	}
 
 	$editor_settings['styles'] = array_merge( $global_styles, get_block_editor_theme_styles() );
@@ -474,9 +487,23 @@ function get_block_editor_settings( array $custom_settings, $block_editor_contex
 		$editor_settings['enableCustomSpacing'] = $editor_settings['__experimentalFeatures']['spacing']['padding'];
 		unset( $editor_settings['__experimentalFeatures']['spacing']['padding'] );
 	}
+	if ( isset( $editor_settings['__experimentalFeatures']['spacing']['customSpacingSize'] ) ) {
+		$editor_settings['disableCustomSpacingSizes'] = ! $editor_ettings['__experimentalFeatures']['spacing']['customSpacingSize'];
+		unset( $editor_settings['__experimentalFeatures']['spacing']['customSpacingSize'] );
+	}
+	if ( isset( $editor_settings['__experimentalFeatures']['spacing']['spacingSizes'] ) ) {
+		$spacing_sizes_by_origin  = $editor_settings['__experimentalFeatures']['spacing']['spacingSizes'];
+		$editor_settings['spacingSizes'] = isset( $spacing_sizes_by_origin['custom'] ) ?
+			$spacing_sizes_by_origin['custom'] : (
+				isset( $spacing_sizes_by_origin['theme'] ) ?
+					$spacing_sizes_by_origin['theme'] :
+					$spacing_sizes_by_origin['default']
+			);
+	}
 
 	$editor_settings['__unstableResolvedAssets']         = _wp_get_iframed_editor_assets();
 	$editor_settings['localAutosaveInterval']            = 15;
+	$editor_settings['disableLayoutStyles']              = current_theme_supports( 'disable-layout-styles' );
 	$editor_settings['__experimentalDiscussionSettings'] = array(
 		'commentOrder'         => get_option( 'comment_order' ),
 		'commentsPerPage'      => get_option( 'comments_per_page' ),

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

@@ -232,6 +232,54 @@ public static function get_theme_data( $deprecated = array(), $options = array()
 		return $with_theme_supports;
 	}
 
+	/**
+	 * Gets the styles for blocks from the block.json file.
+	 *
+	 * @since 6.1.0
+	 *
+	 * @return WP_Theme_JSON
+	 */
+	public static function get_block_data() {
+		$registry = WP_Block_Type_Registry::get_instance();
+		$blocks   = $registry->get_all_registered();
+		$config   = array( 'version' => 1 );
+		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'] );
+			}
+
+			if (
+				isset( $block_type->supports['spacing']['blockGap']['__experimentalDefault'] ) &&
+				null === _wp_array_get( $config, array( 'styles', 'blocks', $block_name, 'spacing', 'blockGap' ), null )
+			) {
+				// Ensure an empty placeholder value exists for the block, if it provides a default blockGap value.
+				// The real blockGap value to be used will be determined when the styles are rendered for output.
+				$config['styles']['blocks'][ $block_name ]['spacing']['blockGap'] = null;
+			}
+		}
+
+		// Core here means it's the lower level part of the styles chain.
+		// It can be a core or a third-party block.
+		return new WP_Theme_JSON( $config, 'core' );
+	}
+
+	/**
+	 * When given an array, this will remove any keys with the name `//`.
+	 *
+	 * @param array $array The array to filter.
+	 * @return array The filtered array.
+	 */
+	private static function remove_json_comments( $array ) {
+		unset( $array['//'] );
+		foreach ( $array as $k => $v ) {
+			if ( is_array( $v ) ) {
+				$array[ $k ] = static::remove_json_comments( $v );
+			}
+		}
+
+		return $array;
+	}
+
 	/**
 	 * Returns the custom post type that contains the user's origin config
 	 * for the active theme or a void array if none are found.
@@ -370,6 +418,7 @@ public static function get_user_data() {
 	 * @since 5.8.0
 	 * @since 5.9.0 Added user data, removed the `$settings` parameter,
 	 *              added the `$origin` parameter.
+	 * @since 6.1.0 Added block data.
 	 *
 	 * @param string $origin Optional. To what level should we merge data.
 	 *                       Valid values are 'theme' or 'custom'. Default 'custom'.
@@ -382,6 +431,7 @@ public static function get_merged_data( $origin = 'custom' ) {
 
 		$result = new WP_Theme_JSON();
 		$result->merge( static::get_core_data() );
+		$result->merge( static::get_block_data() );
 		$result->merge( static::get_theme_data() );
 
 		if ( 'custom' === $origin ) {