Avoid enqueueing scripts and styles for a block unless content is rendered

src/wp-includes/class-wp-block.php

@@ -492,6 +492,14 @@ public function replace_rich_text( $rich_text ) {
 	public function render( $options = array() ) {
  global $post;
 
+ // Capture the current assets queues and then clear out to capture the diff of what was introduced by rendering.
+ $before_styles_queue = wp_styles()->queue;
+ $before_scripts_queue = wp_scripts()->queue;
+ $before_script_modules_queue = wp_script_modules()->queue;
+ wp_styles()->queue = array();
+ wp_scripts()->queue = array();
+ wp_script_modules()->queue = array();
+
  /*
  * There can be only one root interactive block at a time because the rendered HTML of that block contains
  * the rendered HTML of all its inner blocks, including any interactive block.
@@ -661,6 +669,44 @@ public function render( $options = array() ) {
  $root_interactive_block = null;
  }
 
+ // Capture the new assets enqueued during rendering, and restore the queues the state prior to rendering.
+ $new_styles_queue = wp_styles()->queue;
+ $new_scripts_queue = wp_scripts()->queue;
+ $new_script_modules_queue = wp_script_modules()->queue;
+ wp_styles()->queue = $before_styles_queue;
+ wp_scripts()->queue = $before_scripts_queue;
+ wp_script_modules()->queue = $before_script_modules_queue;
+ $has_new_styles = count( $new_styles_queue ) > 0;
+ $has_new_scripts = count( $new_scripts_queue ) > 0;
+ $has_new_script_modules = count( $new_script_modules_queue ) > 0;
+
+ // Merge the newly enqueued assets with the existing assets if the rendered block is not empty.
+ if (
+ ( $has_new_styles || $has_new_scripts || $has_new_script_modules ) &&
+ (
+ trim( $block_content ) !== '' ||
+ /**
+ * Filters whether to enqueue assets for a block which has no rendered content.
+ *
+ * @since 6.9.0
+ *
+ * @param bool $enqueue Whether to enqueue assets.
+ * @param string $block_name Block name.
+ */
+ (bool) apply_filters( 'enqueue_empty_block_content_assets', false, $this->name )
+ )
+ ) {
+ if ( $has_new_styles ) {
+ wp_styles()->queue = array_unique( array_merge( wp_styles()->queue, $new_styles_queue ) );
+ }
+ if ( $has_new_scripts ) {
+ wp_scripts()->queue = array_unique( array_merge( wp_scripts()->queue, $new_scripts_queue ) );
+ }
+ if ( $has_new_script_modules ) {
+ wp_script_modules()->queue = array_unique( array_merge( wp_script_modules()->queue, $new_script_modules_queue ) );
+ }
+ }
+
  return $block_content;
 	}
 }

src/wp-includes/class-wp-script-modules.php

@@ -23,12 +23,12 @@ class WP_Script_Modules {
 	private $registered = array();
 
 	/**
- * Holds the script module identifiers that were enqueued before registered.
+ * An array of IDs for queued script modules.
  *
- * @since 6.5.0
- * @var array<string, true>
+ * @since 6.9.0
+ * @var string[]
  */
-private $enqueued_before_registered = array();
+public $queue = array();
 
 	/**
  * Tracks whether the @wordpress/a11y script module is available.
@@ -122,7 +122,6 @@ public function register( string $id, string $src, array $deps = array(), $versi
  $this->registered[ $id ] = array(
  'src' => $src,
  'version' => $version,
- 'enqueue' => isset( $this->enqueued_before_registered[ $id ] ),
  'dependencies' => $dependencies,
  'fetchpriority' => $fetchpriority,
  );
@@ -213,13 +212,11 @@ public function set_fetchpriority( string $id, string $priority ): bool {
  * }
  */
 	public function enqueue( string $id, string $src = '', array $deps = array(), $version = false, array $args = array() ) {
- if ( isset( $this->registered[ $id ] ) ) {
- $this->registered[ $id ]['enqueue'] = true;
- } elseif ( $src ) {
+ if ( ! in_array( $id, $this->queue, true ) ) {
+ $this->queue[] = $id;
+ }
+ if ( ! isset( $this->registered[ $id ] ) && $src ) {
  $this->register( $id, $src, $deps, $version, $args );
- $this->registered[ $id ]['enqueue'] = true;
- } else {
- $this->enqueued_before_registered[ $id ] = true;
  }
 	}
 
@@ -231,10 +228,7 @@ public function enqueue( string $id, string $src = '', array $deps = array(), $v
  * @param string $id The identifier of the script module.
  */
 	public function dequeue( string $id ) {
- if ( isset( $this->registered[ $id ] ) ) {
- $this->registered[ $id ]['enqueue'] = false;
- }
- unset( $this->enqueued_before_registered[ $id ] );
+ $this->queue = array_diff( $this->queue, array( $id ) );
 	}
 
 	/**
@@ -245,8 +239,8 @@ public function dequeue( string $id ) {
  * @param string $id The identifier of the script module.
  */
 	public function deregister( string $id ) {
+ $this->dequeue( $id );
  unset( $this->registered[ $id ] );
- unset( $this->enqueued_before_registered[ $id ] );
 	}
 
 	/**
@@ -304,9 +298,9 @@ public function print_enqueued_script_modules() {
  * @since 6.5.0
  */
 	public function print_script_module_preloads() {
- foreach ( $this->get_dependencies( array_keys( $this->get_marked_for_enqueue() ), array( 'static' ) ) as $id => $script_module ) {
+ foreach ( $this->get_dependencies( array_unique( $this->queue ), array( 'static' ) ) as $id => $script_module ) {
  // Don't preload if it's marked for enqueue.
- if ( true !== $script_module['enqueue'] ) {
+ if ( ! in_array( $id, $this->queue, true ) ) {
  echo sprintf(
  '<link rel="modulepreload" href="%s" id="%s"%s>',
  esc_url( $this->get_src( $id ) ),
@@ -345,7 +339,7 @@ public function print_import_map() {
  */
 	private function get_import_map(): array {
  $imports = array();
- foreach ( $this->get_dependencies( array_keys( $this->get_marked_for_enqueue() ) ) as $id => $script_module ) {
+ foreach ( $this->get_dependencies( array_unique( $this->queue ) ) as $id => $script_module ) {
  $imports[ $id ] = $this->get_src( $id );
  }
  return array( 'imports' => $imports );
@@ -359,13 +353,10 @@ private function get_import_map(): array {
  * @return array<string, array> Script modules marked for enqueue, keyed by script module identifier.
  */
 	private function get_marked_for_enqueue(): array {
- $enqueued = array();
- foreach ( $this->registered as $id => $script_module ) {
- if ( true === $script_module['enqueue'] ) {
- $enqueued[ $id ] = $script_module;
- }
- }
- return $enqueued;
+ return wp_array_slice_assoc(
+ $this->registered,
+ $this->queue
+ );
 	}
 
 	/**
@@ -457,7 +448,7 @@ private function get_src( string $id ): string {
  */
 	public function print_script_module_data(): void {
  $modules = array();
- foreach ( array_keys( $this->get_marked_for_enqueue() ) as $id ) {
+ foreach ( array_unique( $this->queue ) as $id ) {
  if ( '@wordpress/a11y' === $id ) {
  $this->a11y_available = true;
  }

tests/phpunit/tests/blocks/editor.php

@@ -31,9 +31,21 @@ public function set_up() {
 
  global $post_ID;
  $post_ID = 1;
+
+ global $wp_scripts, $wp_styles;
+ $this->original_wp_scripts = $wp_scripts;
+ $this->original_wp_styles = $wp_styles;
+ $wp_scripts = null;
+ $wp_styles = null;
+ wp_scripts();
+ wp_styles();
 	}
 
 	public function tear_down() {
+ global $wp_scripts, $wp_styles;
+ $wp_scripts = $this->original_wp_scripts;
+ $wp_styles = $this->original_wp_styles;
+
  /** @var WP_REST_Server $wp_rest_server */
  global $wp_rest_server;
  $wp_rest_server = null;
@@ -42,6 +54,16 @@ public function tear_down() {
  parent::tear_down();
 	}
 
+	/**
+ * @var WP_Scripts|null
+ */
+	protected $original_wp_scripts;
+
+	/**
+ * @var WP_Styles|null
+ */
+	protected $original_wp_styles;
+
 	public function filter_set_block_categories_post( $block_categories, $post ) {
  if ( empty( $post ) ) {
  return $block_categories;