Add Post Content attributes as a block editor setting

src/wp-includes/block-editor.php

@@ -361,6 +361,92 @@ function _wp_get_iframed_editor_assets() {
 	);
 }
 
+/**
+ * Finds the first occurrence of a specific block in an array of blocks.
+ *
+ * @since 6.3.0
+ *
+ * @param array  $blocks     Array of blocks.
+ * @param string $block_name Name of the block to find.
+ * @return array Found block, or empty array if none found.
+ */
+function wp_get_first_block( $blocks, $block_name ) {
+	foreach ( $blocks as $block ) {
+		if ( $block_name === $block['blockName'] ) {
+			return $block;
+		}
+		if ( ! empty( $block['innerBlocks'] ) ) {
+			$found_block = wp_get_first_block( $block['innerBlocks'], $block_name );
+
+			if ( ! empty( $found_block ) ) {
+				return $found_block;
+			}
+		}
+	}
+
+	return array();
+}
+
+/**
+ * Retrieves Post Content block attributes from the current post template.
+ *
+ * @since 6.3.0
+ * @access private
+ *
+ * @global int $post_ID
+ *
+ * @return array Post Content block attributes or empty array if they don't exist.
+ */
+function wp_get_post_content_block_attributes() {
+	global $post_ID;
+
+	$is_block_theme = wp_is_block_theme();
+
+	if ( ! $is_block_theme || ! $post_ID ) {
+		return array();
+	}
+
+	$template_slug = get_page_template_slug( $post_ID );
+
+	if ( ! $template_slug ) {
+		$post_slug      = 'singular';
+		$page_slug      = 'singular';
+		$template_types = get_block_templates();
+
+		foreach ( $template_types as $template_type ) {
+			if ( 'page' === $template_type->slug ) {
+				$page_slug = 'page';
+			}
+			if ( 'single' === $template_type->slug ) {
+				$post_slug = 'single';
+			}
+		}
+
+		$what_post_type = get_post_type( $post_ID );
+		switch ( $what_post_type ) {
+			case 'page':
+				$template_slug = $page_slug;
+				break;
+			default:
+				$template_slug = $post_slug;
+				break;
+		}
+	}
+
+	$current_template = get_block_templates( array( 'slug__in' => array( $template_slug ) ) );
+
+	if ( ! empty( $current_template ) ) {
+		$template_blocks    = parse_blocks( $current_template[0]->content );
+		$post_content_block = wp_get_first_block( $template_blocks, 'core/post-content' );
+
+		if ( ! empty( $post_content_block['attrs'] ) ) {
+			return $post_content_block['attrs'];
+		}
+	}
+
+	return array();
+}
+
 /**
  * Returns the contextualized block editor settings for a selected editor context.
  *
@@ -529,6 +615,12 @@ function get_block_editor_settings( array $custom_settings, $block_editor_contex
 		),
 	);
 
+	$post_content_block_attributes = wp_get_post_content_block_attributes();
+
+	if ( ! empty( $post_content_block_attributes ) ) {
+		$editor_settings['postContentAttributes'] = $post_content_block_attributes;
+	}
+
 	/**
 	 * Filters the settings to pass to the block editor for all editor type.
 	 *

tests/phpunit/data/themedir1/block-theme/templates/single.html

@@ -0,0 +1,2 @@
+<!-- wp:post-title {"level":1,"style":{"spacing":{"margin":{"bottom":"var:preset|spacing|40"}}}} /-->
+<!-- wp:post-content {"layout":{"type":"constrained"}} /-->

tests/phpunit/tests/blocks/editor.php

@@ -27,12 +27,17 @@ public function set_up() {
 		global $wp_rest_server;
 		$wp_rest_server = new Spy_REST_Server();
 		do_action( 'rest_api_init', $wp_rest_server );
+
+		global $post_ID;
+		$post_ID = 1;
 	}
 
 	public function tear_down() {
 		/** @var WP_REST_Server $wp_rest_server */
 		global $wp_rest_server;
 		$wp_rest_server = null;
+		global $post_ID;
+		$post_ID = null;
 		parent::tear_down();
 	}
 
@@ -396,6 +401,59 @@ function filter_block_editor_settings_my_editor( $editor_settings ) {
 		$this->assertSame( 12345, $settings['maxUploadFileSize'] );
 	}
 
+	/**
+	 * @ticket 58534
+	 */
+	public function test_wp_get_first_block() {
+		$block_name               = 'core/paragraph';
+		$blocks                   = array(
+			array(
+				'blockName' => 'core/image',
+			),
+			array(
+				'blockName' => $block_name,
+				'attrs'     => array(
+					'content' => 'Hello World!',
+				),
+			),
+			array(
+				'blockName' => 'core/heading',
+			),
+			array(
+				'blockName' => $block_name,
+			),
+		);
+		$blocks_with_no_paragraph = array(
+			array(
+				'blockName' => 'core/image',
+			),
+			array(
+				'blockName' => 'core/heading',
+			),
+		);
+
+		$this->assertSame( $blocks[1], wp_get_first_block( $blocks, $block_name ) );
+
+		$this->assertSame( array(), wp_get_first_block( $blocks_with_no_paragraph, $block_name ) );
+	}
+
+	/**
+	 * @ticket 58534
+	 */
+	public function test_wp_get_post_content_block_attributes() {
+		$attributes_with_layout = array(
+			'layout' => array(
+				'type' => 'constrained',
+			),
+		);
+		// With no block theme, expect an empty array.
+		$this->assertSame( array(), wp_get_post_content_block_attributes() );
+
+		switch_theme( 'block-theme' );
+
+		$this->assertSame( $attributes_with_layout, wp_get_post_content_block_attributes() );
+	}
+
 	/**
 	 * @ticket 53458
 	 */
@@ -456,6 +514,15 @@ public function test_get_block_editor_settings_theme_json_settings() {
 		$this->assertSameSets( array( 'rem' ), $settings['enableCustomUnits'] );
 		// settings.spacing.customPadding
 		$this->assertTrue( $settings['enableCustomSpacing'] );
+		// settings.postContentAttributes
+		$this->assertSameSets(
+			array(
+				'layout' => array(
+					'type' => 'constrained',
+				),
+			),
+			$settings['postContentAttributes']
+		);
 
 		switch_theme( WP_DEFAULT_THEME );
 	}