Add the Block Bindings API

src/wp-includes/block-bindings/sources/pattern.php

@@ -0,0 +1,23 @@
+<?php
+/**
+ * The "pattern" source for the Block Bindings API. This source is used by the
+ * Partially Synced Patterns.
+ *
+ * @since 6.5.0
+ * @package WordPress
+ */
+function pattern_source_callback( $source_attrs, $block_instance, $attribute_name ) {
+	if ( ! _wp_array_get( $block_instance->attributes, array( 'metadata', 'id' ), false ) ) {
+		return null;
+	}
+	$block_id = $block_instance->attributes['metadata']['id'];
+	return _wp_array_get( $block_instance->context, array( 'pattern/overrides', $block_id, $attribute_name ), null );
+}
+
+register_block_bindings_source(
+	'core/pattern-attributes',
+	array(
+		'label'              => __( 'Pattern Attributes' ),
+		'get_value_callback' => 'pattern_source_callback',
+	)
+);

src/wp-includes/block-bindings/sources/post-meta.php

@@ -0,0 +1,33 @@
+<?php
+/**
+ * Add the post_meta source to the Block Bindings API.
+ *
+ * @since 6.5.0
+ * @package WordPress
+ */
+function post_meta_source_callback( $source_attrs ) {
+	// Use the postId attribute if available
+	if ( isset( $source_attrs['postId'] ) ) {
+		$post_id = $source_attrs['postId'];
+	} else {
+		// $block_instance->context['postId'] is not available in the Image block.
+		$post_id = get_the_ID();
+	}
+
+	// If a post isn't public, we need to prevent
+	// unauthorized users from accessing the post meta.
+	$post = get_post( $post_id );
+	if ( ( $post && 'publish' !== $post->post_status && ! current_user_can( 'read_post', $post_id ) ) || post_password_required( $post_id ) ) {
+		return null;
+	}
+
+	return get_post_meta( $post_id, $source_attrs['value'], true );
+}
+
+register_block_bindings_source(
+	'core/post-meta',
+	array(
+		'label'              => _x( 'Post Meta', 'Post metadata to be read and used to substitute block content' ),
+		'get_value_callback' => 'post_meta_source_callback',
+	)
+);

src/wp-includes/class-wp-block.php

@@ -191,6 +191,204 @@ public function __get( $name ) {
 		return null;
 	}
 
+	/**
+	 * Processes the block bindings in block's attributes.
+	 *
+	 * A block might contain bindings in its attributes. Bindings are mappings
+	 * between an attribute of the block and a source. A "source" is a function
+	 * registered with `$this->register()` that defines how to
+	 * retrieve a value from outside the block, e.g. from post meta.
+	 *
+	 * This function will process those bindings and replace the HTML with the value of the binding.
+	 * The value is retrieved from the source of the binding.
+	 *
+	 * ### Example
+	 *
+	 * The "bindings" property for an Image block might look like this:
+	 *
+	 * ```json
+	 * {
+	 *   "metadata": {
+	 *     "bindings": {
+	 *       "title": {
+	 *         "source": {
+	 *           "name": "post_meta",
+	 *           "attributes": { "value": "text_custom_field" }
+	 *         }
+	 *       },
+	 *       "url": {
+	 *         "source": {
+	 *           "name": "post_meta",
+	 *           "attributes": { "value": "url_custom_field" }
+	 *         }
+	 *       }
+	 *     }
+	 *   }
+	 * }
+	 * ```
+	 *
+	 * The above example will replace the `title` and `url` attributes of the Image
+	 * block with the values of the `text_custom_field` and `url_custom_field` post meta.
+	 *
+	 * @access private
+	 * @since 6.5.0
+	 *
+	 * @param string   $block_content Block content.
+	 * @param array    $block The full block, including name and attributes.
+	 */
+	private function process_block_bindings( $block_content ) {
+		$block = $this->parsed_block;
+
+		// Allowed blocks that support block bindings.
+		// TODO: Look for a mechanism to opt-in for this. Maybe adding a property to block attributes?
+		$allowed_blocks = array(
+			'core/paragraph' => array( 'content' ),
+			'core/heading'   => array( 'content' ),
+			'core/image'     => array( 'url', 'title', 'alt' ),
+			'core/button'    => array( 'url', 'text' ),
+		);
+
+		// If the block doesn't have the bindings property or isn't one of the allowed block types, return.
+		if ( ! isset( $block['attrs']['metadata']['bindings'] ) || ! isset( $allowed_blocks[ $this->name ] ) ) {
+			return $block_content;
+		}
+
+		$block_bindings_sources = get_all_registered_block_bindings_sources();
+		$modified_block_content = $block_content;
+		foreach ( $block['attrs']['metadata']['bindings'] as $binding_attribute => $binding_source ) {
+			// If the attribute is not in the list, process next attribute.
+			if ( ! in_array( $binding_attribute, $allowed_blocks[ $this->name ], true ) ) {
+				continue;
+			}
+			// If no source is provided, or that source is not registered, process next attribute.
+			if ( ! isset( $binding_source['source'] ) || ! isset( $binding_source['source']['name'] ) || ! isset( $block_bindings_sources[ $binding_source['source']['name'] ] ) ) {
+				continue;
+			}
+
+			$source_callback = $block_bindings_sources[ $binding_source['source']['name'] ]['get_value_callback'];
+			// Get the value based on the source.
+			if ( ! isset( $binding_source['source']['attributes'] ) ) {
+				$source_args = array();
+			} else {
+				$source_args = $binding_source['source']['attributes'];
+			}
+			$source_value = $source_callback( $source_args, $this, $binding_attribute );
+			// If the value is null, process next attribute.
+			if ( is_null( $source_value ) ) {
+				continue;
+			}
+
+			// Process the HTML based on the block and the attribute.
+			$modified_block_content = $this->replace_html( $modified_block_content, $this->name, $binding_attribute, $source_value );
+		}
+		return $modified_block_content;
+	}
+
+	/**
+	 * Depending on the block attributes, replace the HTML based on the value returned by the source.
+	 *
+	 * @since 6.5.0
+	 *
+	 * @param string $block_content Block content.
+	 * @param string $block_name The name of the block to process.
+	 * @param string $block_attr The attribute of the block we want to process.
+	 * @param string $source_value The value used to replace the HTML.
+	 */
+	private function replace_html( string $block_content, string $block_name, string $block_attr, string $source_value ) {
+		$block_type = WP_Block_Type_Registry::get_instance()->get_registered( $block_name );
+		if ( null === $block_type || ! isset( $block_type->attributes[ $block_attr ] ) ) {
+			return $block_content;
+		}
+
+		// Depending on the attribute source, the processing will be different.
+		switch ( $block_type->attributes[ $block_attr ]['source'] ) {
+			case 'html':
+			case 'rich-text':
+				$block_reader = new WP_HTML_Tag_Processor( $block_content );
+
+				// TODO: Support for CSS selectors whenever they are ready in the HTML API.
+				// In the meantime, support comma-separated selectors by exploding them into an array.
+				$selectors = explode( ',', $block_type->attributes[ $block_attr ]['selector'] );
+				// Add a bookmark to the first tag to be able to iterate over the selectors.
+				$block_reader->next_tag();
+				$block_reader->set_bookmark( 'iterate-selectors' );
+
+				// TODO: This shouldn't be needed when the `set_inner_html` function is ready.
+				// Store the parent tag and its attributes to be able to restore them later in the button.
+				// The button block has a wrapper while the paragraph and heading blocks don't.
+				if ( 'core/button' === $block_name ) {
+					$button_wrapper                 = $block_reader->get_tag();
+					$button_wrapper_attribute_names = $block_reader->get_attribute_names_with_prefix( '' );
+					$button_wrapper_attrs           = array();
+					foreach ( $button_wrapper_attribute_names as $name ) {
+						$button_wrapper_attrs[ $name ] = $block_reader->get_attribute( $name );
+					}
+				}
+
+				foreach ( $selectors as $selector ) {
+					// If the parent tag, or any of its children, matches the selector, replace the HTML.
+					if ( strcasecmp( $block_reader->get_tag( $selector ), $selector ) === 0 || $block_reader->next_tag(
+						array(
+							'tag_name' => $selector,
+						)
+					) ) {
+						$block_reader->release_bookmark( 'iterate-selectors' );
+
+						// TODO: Use `set_inner_html` method whenever it's ready in the HTML API.
+						// Until then, it is hardcoded for the paragraph, heading, and button blocks.
+						// Store the tag and its attributes to be able to restore them later.
+						$selector_attribute_names = $block_reader->get_attribute_names_with_prefix( '' );
+						$selector_attrs           = array();
+						foreach ( $selector_attribute_names as $name ) {
+							$selector_attrs[ $name ] = $block_reader->get_attribute( $name );
+						}
+						$selector_markup = "<$selector>" . wp_kses_post( $source_value ) . "</$selector>";
+						$amended_content = new WP_HTML_Tag_Processor( $selector_markup );
+						$amended_content->next_tag();
+						foreach ( $selector_attrs as $attribute_key => $attribute_value ) {
+							$amended_content->set_attribute( $attribute_key, $attribute_value );
+						}
+						if ( 'core/paragraph' === $block_name || 'core/heading' === $block_name ) {
+							return $amended_content->get_updated_html();
+						}
+						if ( 'core/button' === $block_name ) {
+							$button_markup  = "<$button_wrapper>{$amended_content->get_updated_html()}</$button_wrapper>";
+							$amended_button = new WP_HTML_Tag_Processor( $button_markup );
+							$amended_button->next_tag();
+							foreach ( $button_wrapper_attrs as $attribute_key => $attribute_value ) {
+								$amended_button->set_attribute( $attribute_key, $attribute_value );
+							}
+							return $amended_button->get_updated_html();
+						}
+					} else {
+						$block_reader->seek( 'iterate-selectors' );
+					}
+				}
+				$block_reader->release_bookmark( 'iterate-selectors' );
+				return $block_content;
+
+			case 'attribute':
+				$amended_content = new WP_HTML_Tag_Processor( $block_content );
+				if ( ! $amended_content->next_tag(
+					array(
+						// TODO: build the query from CSS selector.
+						'tag_name' => $block_type->attributes[ $block_attr ]['selector'],
+					)
+				) ) {
+					return $block_content;
+				}
+				$amended_content->set_attribute( $block_type->attributes[ $block_attr ]['attribute'], esc_attr( $source_value ) );
+				return $amended_content->get_updated_html();
+				break;
+
+			default:
+				return $block_content;
+				break;
+		}
+		return;
+	}
+
+
 	/**
 	 * Generates the render output for the block.
 	 *
@@ -280,6 +478,10 @@ public function render( $options = array() ) {
 			}
 		}
 
+		// Process the block bindings for this block, if any are registered. This
+		// will replace the block content with the value from a registered binding source.
+		$block_content = $this->process_block_bindings( $block_content );
+
 		/**
 		 * Filters the content of a single block.
 		 *

src/wp-settings.php

@@ -376,6 +376,8 @@
 require ABSPATH . WPINC . '/fonts.php';
 require ABSPATH . WPINC . '/class-wp-script-modules.php';
 require ABSPATH . WPINC . '/script-modules.php';
+require ABSPATH . WPINC . '/block-bindings/sources/post-meta.php';
+require ABSPATH . WPINC . '/block-bindings/sources/pattern.php';
 
 $GLOBALS['wp_embed'] = new WP_Embed();
 

tests/phpunit/tests/block-bindings.php

@@ -0,0 +1,63 @@
+<?php
+/**
+ * Unit tests covering WP_Block_Bindings_Registry functionality.
+ *
+ * @group block-bindings
+ *
+ * @covers WP_Block_Bindings_Registry
+ *
+ * @since 6.5.0
+ * @package WordPress
+ */
+class WP_Block_Bindings_Registry_Test extends WP_UnitTestCase {
+
+	/**
+	 * Set up before each test.
+	 *
+	 * @since 6.5.0
+	 */
+	public function set_up() {
+		foreach ( get_all_registered_block_bindings_sources() as $source_name => $source_properties ) {
+			unregister_block_bindings_source( $source_name );
+		}
+
+		parent::set_up();
+	}
+
+	/**
+	* Test if the block content is updated with the value returned by the source.
+	*
+	* @since 6.5.0
+	*
+	* @covers WP_Block_Bindings_Registry::
+	*/
+	public function test_replace_html_for_paragraph_content() {
+		$source_name        = 'test/source';
+		$label              = 'Test Source';
+		$get_value_callback = function () {
+			return 'test source value';
+		};
+
+		register_block_bindings_source(
+			$source_name,
+			array(
+				'label'              => $label,
+				'get_value_callback' => $get_value_callback,
+			)
+		);
+
+		$block_content = <<<HTML
+<!-- wp:paragraph {"metadata":{"bindings":{"content":{"source":{"name":"test/source","attributes":{"value":"text_custom_field"}}}}}} --><p>This should not appear</p><!-- /wp:paragraph -->
+HTML;
+
+		$parsed_blocks = parse_blocks( $block_content );
+
+		$block = new WP_Block( $parsed_blocks[0] );
+
+		$expected = '<p>test source value</p>';
+		$result   = $block->render();
+
+		// Check if the block content was updated correctly.
+		$this->assertEquals( $expected, $result, 'The block content should be updated with the value returned by the source.' );
+	}
+}

tests/phpunit/tests/block-bindings/register.php

@@ -16,16 +16,26 @@ class Tests_Block_Bindings_Register extends WP_UnitTestCase {
 		'label' => 'Test source',
 	);
 
+	/**
+	 * Set up before each test.
+	 *
+	 * @since 6.5.0
+	 */
+	public function set_up() {
+		foreach ( get_all_registered_block_bindings_sources() as $source_name => $source_properties ) {
+			unregister_block_bindings_source( $source_name );
+		}
+
+		parent::set_up();
+	}
+
 	/**
 	 * Tear down after each test.
 	 *
 	 * @since 6.5.0
 	 */
 	public function tear_down() {
 		foreach ( get_all_registered_block_bindings_sources() as $source_name => $source_properties ) {
-			if ( str_starts_with( $source_name, 'test/' ) ) {
-				unregister_block_bindings_source( $source_name );
-			}
 			unregister_block_bindings_source( $source_name );
 		}