Ensure that custom block element styles in theme.json are not ignored

src/wp-includes/global-styles-and-settings.php

@@ -320,20 +320,10 @@ function wp_add_global_styles_for_blocks() {
 
 		// The likes of block element styles from theme.json do not have  $metadata['name'] set.
 		if ( ! isset( $metadata['name'] ) && ! empty( $metadata['path'] ) ) {
-			$result = array_values(
-				array_filter(
-					$metadata['path'],
-					static function ( $item ) {
-						if ( str_contains( $item, 'core/' ) ) {
-							return true;
-						}
-						return false;
-					}
-				)
-			);
-			if ( isset( $result[0] ) ) {
-				if ( str_starts_with( $result[0], 'core/' ) ) {
-					$block_name        = str_replace( 'core/', '', $result[0] );
+			$block_name = wp_get_block_name_from_theme_json_path( $metadata['path'] );
+			if ( $block_name ) {
+				if ( str_starts_with( $block_name, 'core/' ) ) {
+					$block_name        = str_replace( 'core/', '', $block_name );
 					$stylesheet_handle = 'wp-block-' . $block_name;
 				}
 				wp_add_inline_style( $stylesheet_handle, $block_css );
@@ -342,6 +332,47 @@ static function ( $item ) {
 	}
 }
 
+/**
+ * Gets the block name from a given theme.json path.
+ *
+ * @since 6.3.0
+ * @access private
+ *
+ * @param array $path An array of keys describing the path to a property in theme.json.
+ * @return string Identified block name, or empty string if none found.
+ */
+function wp_get_block_name_from_theme_json_path( $path ) {
+	// Block name is expected to be the third item after 'styles' and 'blocks'.
+	if (
+		count( $path ) >= 3
+		&& 'styles' === $path[0]
+		&& 'blocks' === $path[1]
+		&& str_contains( $path[2], '/' )
+	) {
+		return $path[2];
+	}
+
+	/*
+	 * As fallback and for backward compatibility, allow any core block to be
+	 * at any position.
+	 */
+	$result = array_values(
+		array_filter(
+			$path,
+			static function ( $item ) {
+				if ( str_contains( $item, 'core/' ) ) {
+					return true;
+				}
+				return false;
+			}
+		)
+	);
+	if ( isset( $result[0] ) ) {
+		return $result[0];
+	}
+	return '';
+}
+
 /**
  * Checks whether a theme or its parent has a theme.json file.
  *

tests/phpunit/data/themedir1/block-theme/theme.json

@@ -73,6 +73,13 @@
 			"my/third-party-block": {
 				"color": {
 					"background": "hotpink"
+				},
+				"elements": {
+					"cite": {
+						"color": {
+							"text": "white"
+						}
+					}
 				}
 			}
 		},

tests/phpunit/tests/theme/wpAddGlobalStylesForBlocks.php

@@ -139,6 +139,88 @@ public function test_blocks_inline_styles_get_rendered() {
 		);
 	}
 
+	/**
+	 * @ticket 57868
+	 */
+	public function test_third_party_blocks_inline_styles_for_elements_get_rendered_when_per_block() {
+		$this->set_up_third_party_block();
+		add_filter( 'should_load_separate_core_block_assets', '__return_true' );
+
+		wp_register_style( 'global-styles', false, array(), true, true );
+		wp_enqueue_style( 'global-styles' );
+		wp_add_global_styles_for_blocks();
+
+		$actual = get_echo( 'wp_print_styles' );
+
+		$this->assertStringContainsString(
+			'.wp-block-my-third-party-block cite{color: white;}',
+			$actual
+		);
+	}
+
+	/**
+	 * @ticket 57868
+	 */
+	public function test_third_party_blocks_inline_styles_for_elements_get_rendered() {
+		wp_register_style( 'global-styles', false, array(), true, true );
+		wp_enqueue_style( 'global-styles' );
+		wp_add_global_styles_for_blocks();
+
+		$actual = get_echo( 'wp_print_styles' );
+
+		$this->assertStringContainsString(
+			'.wp-block-my-third-party-block cite{color: white;}',
+			$actual
+		);
+	}
+
+	/**
+	 * @ticket 57868
+	 *
+	 * @dataProvider data_wp_get_block_name_from_theme_json_path
+	 *
+	 * @param array  $path     An array of keys describing the path to a property in theme.json.
+	 * @param string $expected The expected block name.
+	 */
+	public function test_wp_get_block_name_from_theme_json_path( $path, $expected ) {
+		$block_name = wp_get_block_name_from_theme_json_path( $path );
+		$this->assertSame( $expected, $block_name );
+	}
+
+	/**
+	 * Data provider.
+	 *
+	 * @return array[]
+	 */
+	public function data_wp_get_block_name_from_theme_json_path() {
+		return array(
+			'core block styles'             => array(
+				array( 'styles', 'blocks', 'core/navigation' ),
+				'core/navigation',
+			),
+			'core block element styles'     => array(
+				array( 'styles', 'blocks', 'core/navigation', 'elements', 'link' ),
+				'core/navigation',
+			),
+			'custom block styles'           => array(
+				array( 'styles', 'blocks', 'my/third-party-block' ),
+				'my/third-party-block',
+			),
+			'custom block element styles'   => array(
+				array( 'styles', 'blocks', 'my/third-party-block', 'elements', 'cite' ),
+				'my/third-party-block',
+			),
+			'custom block wrong format'     => array(
+				array( 'styles', 'my/third-party-block' ),
+				'',
+			),
+			'invalid path but works for BC' => array(
+				array( 'something', 'core/image' ),
+				'core/image',
+			),
+		);
+	}
+
 	private function set_up_third_party_block() {
 		switch_theme( 'block-theme' );