Register block style early.

src/wp-admin/includes/upgrade.php

@@ -654,6 +654,8 @@ function wp_upgrade() {
 			update_site_meta( get_current_blog_id(), 'db_last_updated', microtime() );
 		}
 
+		delete_transient( 'wp_core_block_styles' );
+
 		/**
 		 * Fires after a site is fully upgraded.
 		 *

src/wp-includes/blocks.php

@@ -205,6 +205,11 @@ function register_block_style_handle( $metadata, $field_name, $index = 0 ) {
 		$style_handle = $style_handle[ $index ];
 	}
 
+	// If the style handle is already registered, skip re-registering.
+	if ( wp_style_is( $style_handle, 'registered' ) ) {
+		return $style_handle;
+	}
+
 	$style_path      = remove_block_asset_path_prefix( $style_handle );
 	$is_style_handle = $style_handle === $style_path;
 	// Allow only passing style handles for core blocks.
@@ -320,7 +325,7 @@ function register_block_type_from_metadata( $file_or_folder, $args = array() ) {
 	 */
 	static $core_blocks_meta;
 	if ( ! $core_blocks_meta ) {
-		$core_blocks_meta = require_once ABSPATH . WPINC . '/blocks/blocks-json.php';
+		$core_blocks_meta = require ABSPATH . WPINC . '/blocks/blocks-json.php';
 	}
 
 	$metadata_file = ( ! str_ends_with( $file_or_folder, 'block.json' ) ) ?
@@ -368,6 +373,7 @@ function register_block_type_from_metadata( $file_or_folder, $args = array() ) {
 		if ( ! isset( $metadata['style'] ) ) {
 			$metadata['style'] = "wp-block-$block_name";
 		}
+
 		if ( ! isset( $metadata['editorStyle'] ) ) {
 			$metadata['editorStyle'] = "wp-block-{$block_name}-editor";
 		}

src/wp-includes/blocks/index.php

@@ -12,6 +12,94 @@
 require BLOCKS_PATH . 'widget-group.php';
 require BLOCKS_PATH . 'require-dynamic-blocks.php';
 
+/**
+ * Registers core block style handles.
+ *
+ * While {@see register_block_style_handle()} is typically used for that, the way it is
+ * implemented is inefficient for core block styles. Registering those style handles here
+ * avoids unnecessary logic and filesystem lookups in the other function.
+ *
+ * @since 6.3.0
+ */
+function register_core_block_style_handles() {
+	if ( ! wp_should_load_separate_core_block_assets() ) {
+		return;
+	}
+
+	static $core_blocks_meta;
+	if ( ! $core_blocks_meta ) {
+		$core_blocks_meta = require ABSPATH . WPINC . '/blocks/blocks-json.php';
+	}
+
+	$includes_url  = includes_url();
+	$includes_path = ABSPATH . WPINC . '/';
+	$suffix        = wp_scripts_get_suffix();
+	$wp_styles     = wp_styles();
+	$style_fields  = array(
+		'style'       => 'style',
+		'editorStyle' => 'editor',
+	);
+
+	/*
+	 * Ignore transient cache when `WP_DEBUG` is enabled. Why? To avoid interfering with
+	 * the core developer's workflow.
+	 *
+	 * @todo Replace `WP_DEBUG` once an "in development mode" check is available in Core.
+	 */
+	if ( ! WP_DEBUG ) {
+		$transient_name = 'wp_core_block_styles';
+		$files          = get_transient( $transient_name );
+		if ( ! $files ) {
+			$files = glob( __DIR__ . '/**/**.css' );
+			set_transient( $transient_name, $files );
+		}
+	} else {
+		$files = glob( __DIR__ . '/**/**.css' );
+	}
+
+	foreach ( $core_blocks_meta as $name => $schema ) {
+		/** This filter is documented in wp-includes/blocks.php */
+		$schema = apply_filters( 'block_type_metadata', $schema );
+
+		// Backfill these properties similar to `register_block_type_from_metadata()`.
+		if ( ! isset( $schema['style'] ) ) {
+			$schema['style'] = "wp-block-$name";
+		}
+		if ( ! isset( $schema['editorStyle'] ) ) {
+			$schema['editorStyle'] = "wp-block-{$name}-editor";
+		}
+
+		foreach ( $style_fields as $style_field => $filename ) {
+			$style_handle = $schema[ $style_field ];
+			if ( is_array( $style_handle ) ) {
+				continue;
+			}
+
+			$style_path = "blocks/{$name}/{$filename}{$suffix}.css";
+			$path       = $includes_path . $style_path;
+
+			if ( ! in_array( $path, $files, true ) ) {
+				$wp_styles->add(
+					$style_handle,
+					false
+				);
+				continue;
+			}
+
+			$wp_styles->add( $style_handle, $includes_url . $style_path );
+			$wp_styles->add_data( $style_handle, 'path', $path );
+
+			$rtl_file = str_replace( "{$suffix}.css", "-rtl{$suffix}.css", $path );
+			if ( is_rtl() && in_array( $rtl_file, $files, true ) ) {
+				$wp_styles->add_data( $style_handle, 'rtl', 'replace' );
+				$wp_styles->add_data( $style_handle, 'suffix', $suffix );
+				$wp_styles->add_data( $style_handle, 'path', $rtl_file );
+			}
+		}
+	}
+}
+add_action( 'init', 'register_core_block_style_handles', 9 );
+
 /**
  * Registers core block types using metadata files.
  * Dynamic core blocks are registered separately.