Blocks: Introduce a variation of serialize blocks helper with traversing

src/wp-includes/block-template-utils.php

@@ -609,7 +609,7 @@ function _build_block_template_result_from_file( $template_file, $template_type
 	}
 
 	$blocks            = parse_blocks( $template_content );
-	$template->content = serialize_blocks( $blocks, '_inject_theme_attribute_in_template_part_block' );
+	$template->content = traverse_and_serialize_blocks( $blocks, '_inject_theme_attribute_in_template_part_block' );
 
 	return $template;
 }

src/wp-includes/blocks.php

@@ -849,22 +849,16 @@ function get_comment_delimited_block_content( $block_name, $block_attributes, $b
  * instead preserve the markup as parsed.
  *
  * @since 5.3.1
- * @since 6.4.0 The `$callback` parameter was added.
  *
- * @param array         $block    A representative array of a single parsed block object. See WP_Block_Parser_Block.
- * @param callable|null $callback Optional. Callback to run on each block in the tree before serialization. Default null.
+ * @param array $block A representative array of a single parsed block object. See WP_Block_Parser_Block.
  * @return string String of rendered HTML.
  */
-function serialize_block( $block, $callback = null ) {
-	if ( is_callable( $callback ) ) {
-		$block = call_user_func( $callback, $block );
-	}
-
+function serialize_block( $block ) {
 	$block_content = '';
 
 	$index = 0;
 	foreach ( $block['innerContent'] as $chunk ) {
-		$block_content .= is_string( $chunk ) ? $chunk : serialize_block( $block['innerBlocks'][ $index++ ], $callback );
+		$block_content .= is_string( $chunk ) ? $chunk : serialize_block( $block['innerBlocks'][ $index++ ] );
 	}
 
 	if ( ! is_array( $block['attrs'] ) ) {
@@ -883,16 +877,83 @@ function serialize_block( $block, $callback = null ) {
  * parsed blocks.
  *
  * @since 5.3.1
- * @since 6.4.0 The `$callback` parameter was added.
  *
- * @param array[]       $blocks   An array of representative arrays of parsed block objects. See serialize_block().
- * @param callable|null $callback Optional. Callback to run on each block in the tree before serialization. Default null.
+ * @param array[] $blocks An array of representative arrays of parsed block objects. See serialize_block().
+ * @return string String of rendered HTML.
+ */
+function serialize_blocks( $blocks ) {
+	return implode( '', array_map( 'serialize_block', $blocks ) );
+}
+
+/**
+ * Traverses the block applying transformations using the callback provided and returns the content of a block,
+ * including comment delimiters, serializing all attributes from the given parsed block.
+ *
+ * This should be used when there is a need to modify the saved block.
+ * Prefer `serialize_block` when preparing a block to be saved to post content.
+ *
+ * @since 6.4.0
+ *
+ * @see serialize_block()
+ *
+ * @param array    $block    A representative array of a single parsed block object. See WP_Block_Parser_Block.
+ * @param callable $callback Callback to run on each block in the tree before serialization.
+ *                           It is called with the following arguments: $block, $parent_block, $block_index, $chunk_index.
+ * @return string String of rendered HTML.
+ */
+function traverse_and_serialize_block( $block, $callback ) {
+	$block_content = '';
+	$block_index   = 0;
+
+	foreach ( $block['innerContent'] as $chunk_index => $chunk ) {
+		if ( is_string( $chunk ) ) {
+			$block_content .= $chunk;
+		} else {
+			$inner_block = call_user_func(
+				$callback,
+				$block['innerBlocks'][ $block_index ],
+				$block,
+				$block_index,
+				$chunk_index
+			);
+			$block_index++;
+			$block_content .= traverse_and_serialize_block( $inner_block, $callback );
+		}
+	}
+
+	if ( ! is_array( $block['attrs'] ) ) {
+		$block['attrs'] = array();
+	}
+
+	return get_comment_delimited_block_content(
+		$block['blockName'],
+		$block['attrs'],
+		$block_content
+	);
+}
+
+/**
+ * Traverses the blocks applying transformations using the callback provided,
+ * and returns a joined string of the aggregate serialization of the given parsed blocks.
+ *
+ * This should be used when there is a need to modify the saved blocks.
+ * Prefer `serialize_blocks` when preparing blocks to be saved to post content.
+ *
+ * @since 6.4.0
+ *
+ * @see serialize_blocks()
+ *
+ * @param array[]  $blocks   An array of representative arrays of parsed block objects. See serialize_block().
+ * @param callable $callback Callback to run on each block in the tree before serialization.
+ *                           It is called with the following arguments: $block, $parent_block, $block_index, $chunk_index.
  * @return string String of rendered HTML.
  */
-function serialize_blocks( $blocks, $callback = null ) {
+function traverse_and_serialize_blocks( $blocks, $callback ) {
 	$result = '';
 	foreach ( $blocks as $block ) {
-		$result .= serialize_block( $block, $callback );
+		// At the top level, there is no parent block, block index, or chunk index to pass to the callback.
+		$block = call_user_func( $callback, $block );
+		$result .= traverse_and_serialize_block( $block, $callback );
 	}
 	return $result;
 }

tests/phpunit/tests/blocks/serialize.php

@@ -13,14 +13,15 @@ class Tests_Blocks_Serialize extends WP_UnitTestCase {
 
 	/**
 	 * @dataProvider data_serialize_identity_from_parsed
+	 *
+	 * @param string $original Original block markup.
 	 */
 	public function test_serialize_identity_from_parsed( $original ) {
 		$blocks = parse_blocks( $original );
 
-		$actual   = serialize_blocks( $blocks );
-		$expected = $original;
+		$actual = serialize_blocks( $blocks );
 
-		$this->assertSame( $expected, $actual );
+		$this->assertSame( $original, $actual );
 	}
 
 	public function data_serialize_identity_from_parsed() {
@@ -58,13 +59,13 @@ public function test_serialized_block_name() {
 	/**
 	 * @ticket 59327
 	 *
-	 * @covers ::serialize_blocks
+	 * @covers ::traverse_and_serialize_blocks
 	 */
-	public function test_callback_argument() {
+	public function test_traverse_and_serialize_blocks() {
 		$markup = "<!-- wp:outer --><!-- wp:inner {\"key\":\"value\"} -->Example.<!-- /wp:inner -->\n\nExample.\n\n<!-- wp:void /--><!-- /wp:outer -->";
 		$blocks = parse_blocks( $markup );
 
-		$actual = serialize_blocks( $blocks, array( __CLASS__, 'add_attribute_to_inner_block' ) );
+		$actual = traverse_and_serialize_blocks( $blocks, array( __CLASS__, 'add_attribute_to_inner_block' ) );
 
 		$this->assertSame(
 			"<!-- wp:outer --><!-- wp:inner {\"key\":\"value\",\"myattr\":\"myvalue\"} -->Example.<!-- /wp:inner -->\n\nExample.\n\n<!-- wp:void /--><!-- /wp:outer -->",
@@ -78,4 +79,26 @@ public static function add_attribute_to_inner_block( $block ) {
 		}
 		return $block;
 	}
+
+	/**
+	 * @ticket 59327
+	 *
+	 * @covers ::traverse_and_serialize_blocks
+	 *
+	 * @dataProvider data_serialize_identity_from_parsed
+	 *
+	 * @param string $original Original block markup.
+	 */
+	public function test_traverse_and_serialize_identity_from_parsed( $original ) {
+		$blocks = parse_blocks( $original );
+
+		$actual = traverse_and_serialize_blocks(
+			$blocks,
+			function ( $block ) {
+				return $block;
+			}
+		);
+
+		$this->assertSame( $original, $actual );
+	}
 }