diff -r 34716fd837a4 -r be944660c56a wp/wp-includes/block-supports/border.php
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/wp/wp-includes/block-supports/border.php	Wed Sep 21 18:19:35 2022 +0200
@@ -0,0 +1,176 @@
+<?php
+/**
+ * Border block support flag.
+ *
+ * @package WordPress
+ * @since 5.8.0
+ */
+
+/**
+ * Registers the style attribute used by the border feature if needed for block
+ * types that support borders.
+ *
+ * @since 5.8.0
+ * @access private
+ *
+ * @param WP_Block_Type $block_type Block Type.
+ */
+function wp_register_border_support( $block_type ) {
+	// Determine if any border related features are supported.
+	$has_border_support       = block_has_support( $block_type, array( '__experimentalBorder' ) );
+	$has_border_color_support = wp_has_border_feature_support( $block_type, 'color' );
+
+	// Setup attributes and styles within that if needed.
+	if ( ! $block_type->attributes ) {
+		$block_type->attributes = array();
+	}
+
+	if ( $has_border_support && ! array_key_exists( 'style', $block_type->attributes ) ) {
+		$block_type->attributes['style'] = array(
+			'type' => 'object',
+		);
+	}
+
+	if ( $has_border_color_support && ! array_key_exists( 'borderColor', $block_type->attributes ) ) {
+		$block_type->attributes['borderColor'] = array(
+			'type' => 'string',
+		);
+	}
+}
+
+/**
+ * Adds CSS classes and inline styles for border styles to the incoming
+ * attributes array. This will be applied to the block markup in the front-end.
+ *
+ * @since 5.8.0
+ * @access private
+ *
+ * @param WP_Block_Type $block_type       Block type.
+ * @param array         $block_attributes Block attributes.
+ *
+ * @return array Border CSS classes and inline styles.
+ */
+function wp_apply_border_support( $block_type, $block_attributes ) {
+	if ( wp_skip_border_serialization( $block_type ) ) {
+		return array();
+	}
+
+	$classes = array();
+	$styles  = array();
+
+	// Border radius.
+	if (
+		wp_has_border_feature_support( $block_type, 'radius' ) &&
+		isset( $block_attributes['style']['border']['radius'] )
+	) {
+		$border_radius = (int) $block_attributes['style']['border']['radius'];
+		$styles[]      = sprintf( 'border-radius: %dpx;', $border_radius );
+	}
+
+	// Border style.
+	if (
+		wp_has_border_feature_support( $block_type, 'style' ) &&
+		isset( $block_attributes['style']['border']['style'] )
+	) {
+		$border_style = $block_attributes['style']['border']['style'];
+		$styles[]     = sprintf( 'border-style: %s;', $border_style );
+	}
+
+	// Border width.
+	if (
+		wp_has_border_feature_support( $block_type, 'width' ) &&
+		isset( $block_attributes['style']['border']['width'] )
+	) {
+		$border_width = intval( $block_attributes['style']['border']['width'] );
+		$styles[]     = sprintf( 'border-width: %dpx;', $border_width );
+	}
+
+	// Border color.
+	if ( wp_has_border_feature_support( $block_type, 'color' ) ) {
+		$has_named_border_color  = array_key_exists( 'borderColor', $block_attributes );
+		$has_custom_border_color = isset( $block_attributes['style']['border']['color'] );
+
+		if ( $has_named_border_color || $has_custom_border_color ) {
+			$classes[] = 'has-border-color';
+		}
+
+		if ( $has_named_border_color ) {
+			$classes[] = sprintf( 'has-%s-border-color', $block_attributes['borderColor'] );
+		} elseif ( $has_custom_border_color ) {
+			$border_color = $block_attributes['style']['border']['color'];
+			$styles[]     = sprintf( 'border-color: %s;', $border_color );
+		}
+	}
+
+	// Collect classes and styles.
+	$attributes = array();
+
+	if ( ! empty( $classes ) ) {
+		$attributes['class'] = implode( ' ', $classes );
+	}
+
+	if ( ! empty( $styles ) ) {
+		$attributes['style'] = implode( ' ', $styles );
+	}
+
+	return $attributes;
+}
+
+/**
+ * Checks whether serialization of the current block's border properties should
+ * occur.
+ *
+ * @since 5.8.0
+ * @access private
+ *
+ * @param WP_Block_Type $block_type Block type.
+ *
+ * @return boolean
+ */
+function wp_skip_border_serialization( $block_type ) {
+	$border_support = _wp_array_get( $block_type->supports, array( '__experimentalBorder' ), false );
+
+	return is_array( $border_support ) &&
+		array_key_exists( '__experimentalSkipSerialization', $border_support ) &&
+		$border_support['__experimentalSkipSerialization'];
+}
+
+/**
+ * Checks whether the current block type supports the border feature requested.
+ *
+ * If the `__experimentalBorder` support flag is a boolean `true` all border
+ * support features are available. Otherwise, the specific feature's support
+ * flag nested under `experimentalBorder` must be enabled for the feature
+ * to be opted into.
+ *
+ * @since 5.8.0
+ * @access private
+ *
+ * @param WP_Block_Type $block_type Block type to check for support.
+ * @param string        $feature    Name of the feature to check support for.
+ * @param mixed         $default    Fallback value for feature support, defaults to false.
+ *
+ * @return boolean Whether or not the feature is supported.
+ */
+function wp_has_border_feature_support( $block_type, $feature, $default = false ) {
+	// Check if all border support features have been opted into via `"__experimentalBorder": true`.
+	if (
+		property_exists( $block_type, 'supports' ) &&
+		( true === _wp_array_get( $block_type->supports, array( '__experimentalBorder' ), $default ) )
+	) {
+		return true;
+	}
+
+	// Check if the specific feature has been opted into individually
+	// via nested flag under `__experimentalBorder`.
+	return block_has_support( $block_type, array( '__experimentalBorder', $feature ), $default );
+}
+
+// Register the block support.
+WP_Block_Supports::get_instance()->register(
+	'border',
+	array(
+		'register_attribute' => 'wp_register_border_support',
+		'apply'              => 'wp_apply_border_support',
+	)
+);