Lib: Implement server-side block context.

lib/compat.php

@@ -125,3 +125,75 @@ function gutenberg_get_post_from_context() {
 	}
 	return get_post();
 }
+
+/**
+ * Shim that hooks into `pre_render_block` so as to override `render_block`
+ * with a function that passes `render_callback` the block object as an
+ * argument and adds support for block context attributes.
+ *
+ * @param string $pre_render The pre-rendered content. Defaults to null.
+ * @param array  $block      The block being rendered.
+ * @param array  $context    The block context.
+ *
+ * @return string String of rendered HTML.
+ */
+function gutenberg_provide_render_callback_with_block_object( $pre_render, $block, $context = array() ) {
+	global $post;
+
+	$source_block = $block;
+	/** This filter is documented in src/wp-includes/blocks.php */
+	$block         = apply_filters( 'render_block_data', $block, $source_block );
+	$block_type    = WP_Block_Type_Registry::get_instance()->get_registered( $block['blockName'] );
+	$is_dynamic    = $block['blockName'] && null !== $block_type && $block_type->is_dynamic();
+	$block_content = '';
+	$index         = 0;
+
+	if ( ! is_array( $block['attrs'] ) ) {
+		$block['attrs'] = array();
+	}
+
+	$block['context'] = array();
+	$next_context     = $context;
+	if ( $block_type ) {
+		if ( isset( $block_type->context ) ) {
+			foreach ( $block_type->context as $attribute_name => $block_names ) {
+				$block_names = is_array( $block_names ) ? $block_names : array( $block_names );
+				foreach ( $block_names as $block_name ) {
+					if ( isset( $context[ $block_name ][ $attribute_name ] ) ) {
+						$block['context'][ $attribute_name ] = $context[ $block_name ][ $attribute_name ];
+					}
+				}
+			}
+		}
+		if ( isset( $block_type->attributes ) ) {
+			foreach ( $block_type->attributes as $attribute_name => $attribute_config ) {
+				if ( $attribute_config['context'] && isset( $block['attrs'][ $attribute_name ] ) ) {
+					if ( ! isset( $next_context[ $block['blockName'] ] ) ) {
+						$next_context[ $block['blockName'] ] = array();
+					}
+					$next_context[ $block['blockName'] ][ $attribute_name ] = $block['attrs'][ $attribute_name ];
+				}
+			}
+		}
+	}
+
+	foreach ( $block['innerContent'] as $chunk ) {
+		if ( is_string( $chunk ) ) {
+			$block_content .= $chunk;
+		} else {
+			$inner_block    = $block['innerBlocks'][ $index++ ];
+			$block_content .= gutenberg_provide_render_callback_with_block_object( null, $inner_block, $next_context );
+		}
+	}
+
+	if ( $is_dynamic ) {
+		$global_post = $post;
+
+		$prepared_attributes = $block_type->prepare_attributes_for_render( $block['attrs'] );
+		$block_content       = (string) call_user_func( $block_type->render_callback, $prepared_attributes, $block_content, $block );
+		$post                = $global_post;
+	}
+	/** This filter is documented in src/wp-includes/blocks.php */
+	return apply_filters( 'render_block', $block_content, $block );
+}
+add_filter( 'pre_render_block', 'gutenberg_provide_render_callback_with_block_object', 10, 2 );