Add register_theme_feature call to ensure the feature is registered s…

…o it appears in API responses

lib/block-supports/layout.php

@@ -226,23 +226,25 @@ function gutenberg_render_layout_support_flag( $block_content, $block ) {
 		$class_names[] = sanitize_title( $layout_classname );
 	}
 
-	$gap_value = _wp_array_get( $block, array( 'attrs', 'style', 'spacing', 'blockGap' ) );
-	// Skip if gap value contains unsupported characters.
-	// Regex for CSS value borrowed from `safecss_filter_attr`, and used here
-	// because we only want to match against the value, not the CSS attribute.
-	if ( is_array( $gap_value ) ) {
-		foreach ( $gap_value as $key => $value ) {
-			$gap_value[ $key ] = $value && preg_match( '%[\\\(&=}]|/\*%', $value ) ? null : $value;
+	// Only generate Layout styles if the theme has not opted-out.
+	// Attribute-based Layout classnames are output in all cases.
+	if ( ! current_theme_supports( 'disable-layout-styles' ) ) {
+
+		$gap_value = _wp_array_get( $block, array( 'attrs', 'style', 'spacing', 'blockGap' ) );
+		// Skip if gap value contains unsupported characters.
+		// Regex for CSS value borrowed from `safecss_filter_attr`, and used here
+		// because we only want to match against the value, not the CSS attribute.
+		if ( is_array( $gap_value ) ) {
+			foreach ( $gap_value as $key => $value ) {
+				$gap_value[ $key ] = $value && preg_match( '%[\\\(&=}]|/\*%', $value ) ? null : $value;
+			}
+		} else {
+			$gap_value = $gap_value && preg_match( '%[\\\(&=}]|/\*%', $gap_value ) ? null : $gap_value;
 		}
-	} else {
-		$gap_value = $gap_value && preg_match( '%[\\\(&=}]|/\*%', $gap_value ) ? null : $gap_value;
-	}
 
-	$fallback_gap_value = _wp_array_get( $block_type->supports, array( 'spacing', 'blockGap', '__experimentalDefault' ), '0.5em' );
-	$block_spacing      = _wp_array_get( $block, array( 'attrs', 'style', 'spacing' ), null );
+		$fallback_gap_value = _wp_array_get( $block_type->supports, array( 'spacing', 'blockGap', '__experimentalDefault' ), '0.5em' );
+		$block_spacing      = _wp_array_get( $block, array( 'attrs', 'style', 'spacing' ), null );
 
-	// Only generate Layout styles if the theme has not opted-out.
-	if ( ! current_theme_supports( 'disable-layout-styles' ) ) {
 		// If a block's block.json skips serialization for spacing or spacing.blockGap,
 		// don't apply the user-defined value to the styles.
 		$should_skip_gap_serialization = gutenberg_should_skip_block_supports_serialization( $block_type, 'spacing', 'blockGap' );

lib/compat/wordpress-6.1/theme.php

@@ -0,0 +1,31 @@
+<?php
+/**
+ * Temporary compatibility shims for features present in Gutenberg.
+ * This file should be removed when WordPress 6.1.0 becomes the lowest
+ * supported version by this plugin.
+ *
+ * @package gutenberg
+ */
+
+/**
+ * This function runs in addition to the core `create_initial_theme_features`.
+ * The 6.1 release needs to update the core function to include the body of this function.
+ *
+ * Creates the initial theme features when the 'setup_theme' action is fired.
+ *
+ * See {@see 'setup_theme'}.
+ *
+ * @since 5.5.0
+ * @since 6.0.1 The `block-templates` feature was added.
+ * @since 6.1.0 The `disable-layout-styles` feature was added.
+ */
+function gutenberg_create_initial_theme_features() {
+	register_theme_feature(
+		'disable-layout-styles',
+		array(
+			'description'  => __( 'Whether the theme disables generated layout styles.', 'gutenberg' ),
+			'show_in_rest' => true,
+		)
+	);
+}
+add_action( 'setup_theme', 'gutenberg_create_initial_theme_features', 0 );

lib/load.php

@@ -88,6 +88,7 @@ function gutenberg_is_experiment_enabled( $name ) {
 require __DIR__ . '/compat/wordpress-6.1/date-settings.php';
 require __DIR__ . '/compat/wordpress-6.1/block-patterns.php';
 require __DIR__ . '/compat/wordpress-6.1/edit-form-blocks.php';
+require __DIR__ . '/compat/wordpress-6.1/theme.php';
 
 // Experimental features.
 remove_action( 'plugins_loaded', '_wp_theme_json_webfonts_handler' ); // Turns off WP 6.0's stopgap handler for Webfonts API.