Extend conditional loading of block global styles to third-party blocks

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

@@ -243,6 +243,38 @@ function wp_get_global_stylesheet( $types = array() ) {
 	return $stylesheet;
 }
 
+/**
+ * Generate the stylesheet handle for a block.
+ *
+ * @since 6.9.0
+ * @access private
+ *
+ * Examples:
+ * - 'core/paragraph' → 'wp-block-paragraph'
+ * - 'paragraph' → 'wp-block-paragraph' (implicit core)
+ * - 'my-plugin/custom-block' → 'wp-block-my-plugin-custom-block'
+ * - '' → null (invalid)
+ *
+ * @param string $block_name The block name.
+ * @return string|null The stylesheet handle or null if invalid.
+ */
+function wp_generate_block_stylesheet_handle( $block_name ) {
+	if ( ! is_string( $block_name ) || empty( $block_name ) ) {
+		return null;
+	}
+
+	// Handle implicit core namespace (e.g., "paragraph" → "core/paragraph").
+	if ( ! str_contains( $block_name, '/' ) ) {
+		$block_name = "core/{$block_name}";
+	}
+
+	// Strip core/ prefix and convert remaining slashes to dashes.
+	$block_name = str_replace( 'core/', '', $block_name );
+	$handle = str_replace( '/', '-', $block_name );
+
+	return "wp-block-{$handle}";
+}
+
 /**
  * Adds global style rules to the inline style for each block.
  *
@@ -312,33 +344,48 @@ function wp_add_global_styles_for_blocks() {
 		 * Block-specific global styles should be attached to the global-styles handle, but
 		 * only for blocks on the page, thus we check if the block's handle is in the queue
 		 * before adding the inline style.
-		 * This conditional loading only applies to core blocks.
-		 * TODO: Explore how this could be expanded to third-party blocks as well.
+		 * This conditional loading applies to both core and third-party blocks.
 		 */
 		if ( isset( $metadata['name'] ) ) {
-			if ( str_starts_with( $metadata['name'], 'core/' ) ) {
-				$block_name   = str_replace( 'core/', '', $metadata['name'] );
-				$block_handle = 'wp-block-' . $block_name;
-				if ( in_array( $block_handle, $wp_styles->queue, true ) ) {
+			$block_handle = wp_generate_block_stylesheet_handle( $metadata['name'] );
+
+			if ( $block_handle && in_array( $block_handle, $wp_styles->queue, true ) ) {
+				wp_add_inline_style( $stylesheet_handle, $block_css );
+			} elseif ( ! $block_handle ) {
+				// Fallback for blocks with unexpected naming patterns.
+				wp_add_inline_style( $stylesheet_handle, $block_css );
+			} else {
+				/*
+				 * For third-party blocks, load styles if the block handle was generated successfully
+				 * but not found in queue. This maintains backward compatibility where third-party
+				 * block styles were always loaded.
+				 */
+				if ( ! str_starts_with( $metadata['name'], 'core/' ) ) {
 					wp_add_inline_style( $stylesheet_handle, $block_css );
 				}
-			} else {
-				wp_add_inline_style( $stylesheet_handle, $block_css );
 			}
 		}
 
 		// The likes of block element styles from theme.json do not have  $metadata['name'] set.
 		if ( ! isset( $metadata['name'] ) && ! empty( $metadata['path'] ) ) {
 			$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 );
-					$block_handle = 'wp-block-' . $block_name;
-					if ( in_array( $block_handle, $wp_styles->queue, true ) ) {
+				$block_handle = wp_generate_block_stylesheet_handle( $block_name );
+
+				if ( $block_handle && in_array( $block_handle, $wp_styles->queue, true ) ) {
+					wp_add_inline_style( $stylesheet_handle, $block_css );
+				} elseif ( ! $block_handle ) {
+					// Fallback for blocks with unexpected naming patterns.
+					wp_add_inline_style( $stylesheet_handle, $block_css );
+				} else {
+					/*
+					 * For third-party blocks, load styles if the block handle was generated successfully
+					 * but not found in queue. This maintains backward compatibility where third-party
+					 * block styles were always loaded.
+					 */
+					if ( ! str_starts_with( $block_name, 'core/' ) ) {
 						wp_add_inline_style( $stylesheet_handle, $block_css );
 					}
-				} else {
-					wp_add_inline_style( $stylesheet_handle, $block_css );
 				}
 			}
 		}