Block Bindings API: Add block bindings PHP registration mechanisms and "Post meta" source under the experimental flag

lib/block-supports/pattern.php

@@ -13,7 +13,7 @@
 	 * @param WP_Block_Type $block_type Block Type.
 	 */
 	function gutenberg_register_pattern_support( $block_type ) {
-		$pattern_support = property_exists( $block_type, 'supports' ) ? _wp_array_get( $block_type->supports, array( '__experimentalConnections' ), false ) : false;
+		$pattern_support = 'core/paragraph' === $block_type->name ? true : false;
 
 		if ( $pattern_support ) {
 			if ( ! $block_type->uses_context ) {

lib/experimental/block-bindings/html-processing.php

@@ -0,0 +1,110 @@
+<?php
+/**
+ * Define the mechanism to replace the HTML depending on the block attributes.
+ *
+ * @package gutenberg
+ */
+
+if ( ! function_exists( 'block_bindings_replace_html' ) ) {
+	/**
+	 * Depending on the block attributes, replace the proper HTML based on the value returned by the source.
+	 *
+	 * @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.
+	 */
+	function block_bindings_replace_html( $block_content, $block_name, $block_attr, $source_value ) {
+		$block_type = WP_Block_Type_Registry::get_instance()->get_registered( $block_name );
+		if ( null === $block_type ) {
+			return;
+		}
+
+		// 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>" . esc_html( $source_value ) . "</$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;
+	}
+}

lib/experimental/block-bindings/index.php

@@ -0,0 +1,20 @@
+<?php
+/**
+ * Require the necessary files.
+ *
+ * @package gutenberg
+ */
+
+require_once __DIR__ . '/sources/index.php';
+require_once __DIR__ . '/html-processing.php';
+
+// Register the sources.
+$gutenberg_experiments = get_option( 'gutenberg-experiments' );
+if ( $gutenberg_experiments ) {
+	if ( array_key_exists( 'gutenberg-pattern-partial-syncing', $gutenberg_experiments ) ) {
+		require_once __DIR__ . '/sources/pattern.php';
+	}
+	if ( array_key_exists( 'gutenberg-block-bindings', $gutenberg_experiments ) ) {
+		require_once __DIR__ . '/sources/post-meta.php';
+	}
+}

lib/experimental/block-bindings/sources/index.php

@@ -0,0 +1,32 @@
+<?php
+/**
+ * Define the mechanism to add new sources available in the block bindings API.
+ *
+ * @package gutenberg
+ */
+
+global $block_bindings_sources;
+$block_bindings_sources = array();
+if ( ! function_exists( 'register_block_bindings_source' ) ) {
+	/**
+	 * Function to register a new source.
+	 *
+	 * @param string   $source_name The name of the source.
+	 * @param string   $label The label of the source.
+	 * @param callable(object, object, string): string $apply - The callback executed when the source is processed during block rendering.
+	 *                        - object $source_attrs: Object containing source ID used to look up the override value, i.e. {"value": "{ID}"}.
+	 *                        - object $block_instance: The block instance.
+	 *                        - string $attribute_name: The name of an attribute used to retrieve an override value from the block context.
+	 *                        The callable should return a string that will be used to override the block's original value.
+	 *
+	 *
+	 * @return void
+	 */
+	function register_block_bindings_source( $source_name, $label, $apply ) {
+		global $block_bindings_sources;
+		$block_bindings_sources[ $source_name ] = array(
+			'label' => $label,
+			'apply' => $apply,
+		);
+	}
+}

lib/experimental/block-bindings/sources/pattern.php

@@ -0,0 +1,21 @@
+<?php
+/**
+ * Add the metadata source to the block bindings API.
+ *
+ * @package gutenberg
+ */
+
+if ( function_exists( 'register_block_bindings_source' ) ) {
+	$pattern_source_callback = function ( $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(
+		'pattern_attributes',
+		__( 'Pattern Attributes', 'gutenberg' ),
+		$pattern_source_callback
+	);
+}

lib/experimental/block-bindings/sources/post-meta.php

@@ -0,0 +1,25 @@
+<?php
+/**
+ * Add the post_meta source to the block bindings API.
+ *
+ * @package gutenberg
+ */
+
+if ( function_exists( 'register_block_bindings_source' ) ) {
+	$post_meta_source_callback = function ( $source_attrs ) {
+		// Use the postId attribute if available
+		if ( isset( $source_attrs['postId'] ) ) {
+			$post_id = $source_attrs['postId'];
+		} else {
+			// I tried using $block_instance->context['postId'] but it wasn't available in the image block.
+			$post_id = get_the_ID();
+		}
+
+		return get_post_meta( $post_id, $source_attrs['value'], true );
+	};
+	register_block_bindings_source(
+		'post_meta',
+		__( 'Post Meta', 'gutenberg' ),
+		$post_meta_source_callback
+	);
+}