Block support: Add server-side processing for anchor

src/wp-includes/block-supports/anchor.php

@@ -0,0 +1,71 @@
+<?php
+/**
+ * Anchor block support flag.
+ *
+ * @package WordPress
+ * @since 7.0.0
+ */
+
+/**
+ * Registers the anchor block attribute for block types that support it.
+ *
+ * @since 7.0.0
+ * @access private
+ *
+ * @param WP_Block_Type $block_type Block Type.
+ */
+function wp_register_anchor_support( $block_type ) {
+	$has_anchor_support = block_has_support( $block_type, array( 'anchor' ), false );
+
+	if ( ! $has_anchor_support ) {
+		return;
+	}
+
+	if ( ! $block_type->attributes ) {
+		$block_type->attributes = array();
+	}
+
+	if ( ! array_key_exists( 'anchor', $block_type->attributes ) ) {
+		$block_type->attributes['anchor'] = array(
+			'type' => 'string',
+		);
+	}
+}
+
+/**
+ * Add the anchor id to the output.
+ *
+ * @since 7.0.0
+ * @access private
+ *
+ * @param WP_Block_Type $block_type       Block Type.
+ * @param array         $block_attributes Block attributes.
+ *
+ * @return array Block anchor id.
+ */
+function wp_apply_anchor_support( $block_type, $block_attributes ) {
+	if ( ! $block_attributes ) {
+		return array();
+	}
+
+	$has_anchor_support = block_has_support( $block_type, array( 'anchor' ), false );
+	if ( ! $has_anchor_support ) {
+		return array();
+	}
+
+	$has_anchor = array_key_exists( 'anchor', $block_attributes );
+	if ( ! $has_anchor || empty( $block_attributes['anchor'] ) ) {
+		return array();
+	}
+
+	return array( 'id' => $block_attributes['anchor'] );
+}
+
+// Register the block support.
+WP_Block_Supports::get_instance()->register(
+	'anchor',
+	array(
+		'register_attribute' => 'wp_register_anchor_support',
+		'apply'              => 'wp_apply_anchor_support',
+	)
+);

src/wp-settings.php

@@ -404,6 +404,7 @@
 require ABSPATH . WPINC . '/block-supports/background.php';
 require ABSPATH . WPINC . '/block-supports/block-style-variations.php';
 require ABSPATH . WPINC . '/block-supports/aria-label.php';
+require ABSPATH . WPINC . '/block-supports/anchor.php';
 require ABSPATH . WPINC . '/block-supports/block-visibility.php';
 require ABSPATH . WPINC . '/style-engine.php';
 require ABSPATH . WPINC . '/style-engine/class-wp-style-engine.php';

tests/phpunit/tests/block-supports/anchor..php

@@ -0,0 +1,85 @@
+<?php
+/**
+ * @group block-supports
+ *
+ * @covers ::wp_apply_anchor_support
+ */
+class Tests_Block_Supports_Anchor extends WP_UnitTestCase {
+	/**
+	 * @var string|null
+	 */
+	private $test_block_name;
+
+	public function set_up() {
+		parent::set_up();
+		$this->test_block_name = null;
+	}
+
+	public function tear_down() {
+		unregister_block_type( $this->test_block_name );
+		$this->test_block_name = null;
+		parent::tear_down();
+	}
+
+	/**
+	 * Registers a new block for testing anchor support.
+	 *
+	 * @param string $block_name Name for the test block.
+	 * @param array  $supports   Array defining block support configuration.
+	 *
+	 * @return WP_Block_Type The block type for the newly registered test block.
+	 */
+	private function register_anchor_block_with_support( $block_name, $supports = array() ) {
+		$this->test_block_name = $block_name;
+		register_block_type(
+			$this->test_block_name,
+			array(
+				'api_version' => 3,
+				'supports'    => $supports,
+			)
+		);
+		$registry = WP_Block_Type_Registry::get_instance();
+
+		return $registry->get_registered( $this->test_block_name );
+	}
+
+	/**
+	 * Tests that anchor block support works as expected.
+	 *
+	 * @dataProvider data_anchor_block_support
+	 *
+	 * @param boolean|array $support  Anchor block support configuration.
+	 * @param string        $value    Anchor value for attribute object.
+	 * @param array         $expected Expected anchor block support output.
+	 */
+	public function test_wp_apply_anchor_support( $support, $value, $expected ) {
+		$block_type  = self::register_anchor_block_with_support(
+			'test/anchor-block',
+			array( 'anchor' => $support )
+		);
+		$block_attrs = array( 'anchor' => $value );
+		$actual      = wp_apply_anchor_support( $block_type, $block_attrs );
+
+		$this->assertSame( $expected, $actual );
+	}
+
+	/**
+	 * Data provider.
+	 *
+	 * @return array
+	 */
+	public function data_anchor_block_support() {
+		return array(
+			'anchor id attribute is applied' => array(
+				'support'  => true,
+				'value'    => 'my-anchor',
+				'expected' => array( 'id' => 'my-anchor' ),
+			),
+			'anchor id attribute is not applied if block does not support it' => array(
+				'support'  => false,
+				'value'    => 'my-anchor',
+				'expected' => array(),
+			),
+		);
+	}
+}