wp_hoist_late_printed_styles()

Source

function wp_hoist_late_printed_styles(): void {
	// Skip the embed template on-demand styles aren't relevant, and there is no wp_head action.
	if ( is_embed() ) {
		return;
	}

	/*
	 * Add a placeholder comment into the inline styles for wp-block-library, after which the late block styles
	 * can be hoisted from the footer to be printed in the header by means of a filter below on the template enhancement
	 * output buffer.
	 *
	 * Note that wp_maybe_inline_styles() prepends the inlined style to the extra 'after' array, which happens after
	 * this code runs. This ensures that the placeholder appears right after any inlined wp-block-library styles,
	 * which would be common.css.
	 */
	$placeholder = sprintf( '/*%s*/', uniqid( 'wp_block_styles_on_demand_placeholder:' ) );
	$dependency  = wp_styles()->query( 'wp-block-library', 'registered' );
	if ( $dependency ) {
		if ( ! isset( $dependency->extra['after'] ) ) {
			wp_add_inline_style( 'wp-block-library', $placeholder );
		} else {
			array_unshift( $dependency->extra['after'], $placeholder );
		}
	}

	/*
	 * Create a substitute for `print_late_styles()` which is aware of block styles. This substitute does not print
	 * the styles, but it captures what would be printed for block styles and non-block styles so that they can be
	 * later hoisted to the HEAD in the template enhancement output buffer. This will run at `wp_print_footer_scripts`
	 * before `print_footer_scripts()` is called.
	 */
	$printed_core_block_styles  = '';
	$printed_other_block_styles = '';
	$printed_global_styles      = '';
	$printed_late_styles        = '';

	$capture_late_styles = static function () use ( &$printed_core_block_styles, &$printed_other_block_styles, &$printed_global_styles, &$printed_late_styles ) {
		// Gather the styles related to on-demand block enqueues.
		$all_core_block_style_handles  = array();
		$all_other_block_style_handles = array();
		foreach ( WP_Block_Type_Registry::get_instance()->get_all_registered() as $block_type ) {
			if ( str_starts_with( $block_type->name, 'core/' ) ) {
				foreach ( $block_type->style_handles as $style_handle ) {
					$all_core_block_style_handles[] = $style_handle;
				}
			} else {
				foreach ( $block_type->style_handles as $style_handle ) {
					$all_other_block_style_handles[] = $style_handle;
				}
			}
		}

		/*
		 * First print all styles related to core blocks which should be inserted right after the wp-block-library stylesheet
		 * to preserve the CSS cascade. The logic in this `if` statement is derived from `wp_print_styles()`.
		 */
		$enqueued_core_block_styles = array_values( array_intersect( $all_core_block_style_handles, wp_styles()->queue ) );
		if ( count( $enqueued_core_block_styles ) > 0 ) {
			ob_start();
			wp_styles()->do_items( $enqueued_core_block_styles );
			$printed_core_block_styles = (string) ob_get_clean();
		}

		// Capture non-core block styles so they can get printed at the point where wp_enqueue_registered_block_scripts_and_styles() runs.
		$enqueued_other_block_styles = array_values( array_intersect( $all_other_block_style_handles, wp_styles()->queue ) );
		if ( count( $enqueued_other_block_styles ) > 0 ) {
			ob_start();
			wp_styles()->do_items( $enqueued_other_block_styles );
			$printed_other_block_styles = (string) ob_get_clean();
		}

		// Capture the global-styles so that it can be printed at the point where wp_enqueue_global_styles() runs.
		if ( wp_style_is( 'global-styles' ) ) {
			ob_start();
			wp_styles()->do_items( array( 'global-styles' ) );
			$printed_global_styles = (string) ob_get_clean();
		}

		/*
		 * Print all remaining styles not related to blocks. This contains a subset of the logic from
		 * `print_late_styles()`, without admin-specific logic and the `print_late_styles` filter to control whether
		 * late styles are printed (since they are being hoisted anyway).
		 */
		ob_start();
		wp_styles()->do_footer_items();
		$printed_late_styles = (string) ob_get_clean();
	};

	/*
	 * If `_wp_footer_scripts()` was unhooked from the `wp_print_footer_scripts` action, or if `wp_print_footer_scripts()`
	 * was unhooked from running at the `wp_footer` action, then only add a callback to `wp_footer` which will capture the
	 * late-printed styles.
	 *
	 * Otherwise, in the normal case where `_wp_footer_scripts()` will run at the `wp_print_footer_scripts` action, then
	 * swap out `_wp_footer_scripts()` with an alternative which captures the printed styles (for hoisting to HEAD) before
	 * proceeding with printing the footer scripts.
	 */
	$wp_print_footer_scripts_priority = has_action( 'wp_print_footer_scripts', '_wp_footer_scripts' );
	if ( false === $wp_print_footer_scripts_priority || false === has_action( 'wp_footer', 'wp_print_footer_scripts' ) ) {
		// The normal priority for wp_print_footer_scripts() is to run at 20.
		add_action( 'wp_footer', $capture_late_styles, 20 );
	} else {
		remove_action( 'wp_print_footer_scripts', '_wp_footer_scripts', $wp_print_footer_scripts_priority );
		add_action(
			'wp_print_footer_scripts',
			static function () use ( $capture_late_styles ) {
				$capture_late_styles();
				print_footer_scripts();
			},
			$wp_print_footer_scripts_priority
		);
	}

	// Replace placeholder with the captured late styles.
	add_filter(
		'wp_template_enhancement_output_buffer',
		static function ( $buffer ) use ( $placeholder, &$printed_core_block_styles, &$printed_other_block_styles, &$printed_global_styles, &$printed_late_styles ) {

			// Anonymous subclass of WP_HTML_Tag_Processor which exposes underlying bookmark spans.
			$processor = new class( $buffer ) extends WP_HTML_Tag_Processor {
				/**
				 * Gets the span for the current token.
				 *
				 * @return WP_HTML_Span Current token span.
				 */
				private function get_span(): WP_HTML_Span {
					// Note: This call will never fail according to the usage of this class, given it is always called after ::next_tag() is true.
					$this->set_bookmark( 'here' );
					return $this->bookmarks['here'];
				}

				/**
				 * Inserts text before the current token.
				 *
				 * @param string $text Text to insert.
				 */
				public function insert_before( string $text ): void {
					$this->lexical_updates[] = new WP_HTML_Text_Replacement( $this->get_span()->start, 0, $text );
				}

				/**
				 * Inserts text after the current token.
				 *
				 * @param string $text Text to insert.
				 */
				public function insert_after( string $text ): void {
					$span = $this->get_span();

					$this->lexical_updates[] = new WP_HTML_Text_Replacement( $span->start + $span->length, 0, $text );
				}

				/**
				 * Removes the current token.
				 */
				public function remove(): void {
					$span = $this->get_span();

					$this->lexical_updates[] = new WP_HTML_Text_Replacement( $span->start, $span->length, '' );
				}

				/**
				 * Replaces the current token.
				 *
				 * @param string $text Text to replace with.
				 */
				public function replace( string $text ): void {
					$span = $this->get_span();

					$this->lexical_updates[] = new WP_HTML_Text_Replacement( $span->start, $span->length, $text );
				}
			};

			// Locate the insertion points in the HEAD.
			while ( $processor->next_tag( array( 'tag_closers' => 'visit' ) ) ) {
				if (
					'STYLE' === $processor->get_tag() &&
					'wp-global-styles-placeholder-inline-css' === $processor->get_attribute( 'id' )
				) {
					/** This is added in wp_enqueue_global_styles() */
					$processor->set_bookmark( 'wp_global_styles_placeholder' );
				} elseif (
					'STYLE' === $processor->get_tag() &&
					'wp-block-styles-placeholder-inline-css' === $processor->get_attribute( 'id' )
				) {
					/** This is added in wp_enqueue_registered_block_scripts_and_styles() */
					$processor->set_bookmark( 'wp_block_styles_placeholder' );
				} elseif (
					'STYLE' === $processor->get_tag() &&
					'wp-block-library-inline-css' === $processor->get_attribute( 'id' )
				) {
					/** This is added here in wp_hoist_late_printed_styles() */
					$processor->set_bookmark( 'wp_block_library' );
				} elseif ( 'HEAD' === $processor->get_tag() && $processor->is_tag_closer() ) {
					$processor->set_bookmark( 'head_end' );
					break;
				}
			}

			/**
			 * Replace the placeholder for global styles enqueued during wp_enqueue_global_styles(). This is done
			 * even if $printed_global_styles is empty.
			 */
			if ( $processor->has_bookmark( 'wp_global_styles_placeholder' ) ) {
				$processor->seek( 'wp_global_styles_placeholder' );
				$processor->replace( $printed_global_styles );
				$printed_global_styles = '';
			}

			/*
			 * Insert block styles right after wp-block-library (if it is present). The placeholder CSS comment will
			 * always be added to the wp-block-library inline style since it gets printed at `wp_head` before the blocks
			 * are rendered. This means that there may not actually be any block styles to hoist from the footer to
			 * insert after this inline style. The placeholder CSS comment needs to be added so that the inline style
			 * gets printed, but if the resulting inline style is empty after the placeholder is removed, then the
			 * inline style is removed.
			 */
			if ( $processor->has_bookmark( 'wp_block_library' ) ) {
				$processor->seek( 'wp_block_library' );

				$css_text = $processor->get_modifiable_text();

				/*
				 * Split the block library inline style by the placeholder to identify the original inlined CSS, which
				 * likely would be common.css, followed by any inline styles which had been added by the theme or
				 * plugins via `wp_add_inline_style( 'wp-block-library', '...' )`. The separate block styles loaded on
				 * demand will get inserted after the inlined common.css and before the extra inline styles added by the
				 * user.
				 */
				$css_text_around_placeholder = explode( $placeholder, $css_text, 2 );
				$extra_inline_styles         = '';
				if ( count( $css_text_around_placeholder ) === 2 ) {
					$css_text = $css_text_around_placeholder[0];
					if ( '' !== trim( $css_text ) ) {
						$inlined_src = wp_styles()->get_data( 'wp-block-library', 'inlined_src' );
						if ( $inlined_src ) {
							$css_text .= sprintf(
								"\n/*# sourceURL=%s */\n",
								esc_url_raw( $inlined_src )
							);
						}
					}
					$extra_inline_styles = $css_text_around_placeholder[1];
				}

				/*
				 * The placeholder CSS comment was added to the inline style in order to force an inline STYLE tag to
				 * be printed. Now that the inline style has been located and the placeholder comment has been removed, if
				 * there is no CSS left in the STYLE tag after removal, then remove the STYLE tag entirely.
				 */
				if ( '' === trim( $css_text ) ) {
					$processor->remove();
				} else {
					$processor->set_modifiable_text( $css_text );
				}

				$inserted_after            = $printed_core_block_styles;
				$printed_core_block_styles = '';

				/*
				 * Add a new inline style for any user styles added via wp_add_inline_style( 'wp-block-library', '...' ).
				 * This must be added here after $printed_core_block_styles to preserve the original CSS cascade when
				 * the combined block library stylesheet was used. The pattern here is checking to see if it is not just
				 * a sourceURL comment after the placeholder above is removed.
				 */
				if ( ! preg_match( ':^\s*(/\*# sourceURL=\S+? \*/\s*)?$:s', $extra_inline_styles ) ) {
					$style_processor = new WP_HTML_Tag_Processor( '<style></style>' );
					$style_processor->next_tag();
					$style_processor->set_attribute( 'id', 'wp-block-library-inline-css-extra' );
					$style_processor->set_modifiable_text( $extra_inline_styles );
					$inserted_after .= "{$style_processor->get_updated_html()}\n";
				}

				if ( '' !== $inserted_after ) {
					$processor->insert_after( "\n" . $inserted_after );
				}
			}

			// Insert block styles at the point where wp_enqueue_registered_block_scripts_and_styles() normally enqueues styles.
			if ( $processor->has_bookmark( 'wp_block_styles_placeholder' ) ) {
				$processor->seek( 'wp_block_styles_placeholder' );
				if ( '' !== $printed_other_block_styles ) {
					$processor->replace( "\n" . $printed_other_block_styles );
				} else {
					$processor->remove();
				}
				$printed_other_block_styles = '';
			}

			// Print all remaining styles.
			$remaining_styles = $printed_core_block_styles . $printed_other_block_styles . $printed_global_styles . $printed_late_styles;
			if ( $remaining_styles && $processor->has_bookmark( 'head_end' ) ) {
				$processor->seek( 'head_end' );
				$processor->insert_before( $remaining_styles . "\n" );
			}
			return $processor->get_updated_html();
		}
	);
}

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