[Fonts API] Automatically enqueue user-selected fonts (#50297)

* Adds user-select fonts enqueuer
* Auto queue before printing
* Always set $handles to false when empty

lib/experimental/fonts-api/class-wp-fonts-resolver.php

@@ -0,0 +1,102 @@
+<?php
+/**
+ * WP_Fonts_Resolver class.
+ *
+ * @package    WordPress
+ * @subpackage Fonts API
+ * @since      X.X.X
+ */
+
+if ( class_exists( 'WP_Fonts_Resolver' ) ) {
+	return;
+}
+
+/**
+ * The Fonts API Resolver abstracts the processing of different data sources
+ * (such as theme.json and global styles) for font interactions with the API.
+ *
+ * This class is for internal core usage and is not supposed to be used by
+ * extenders (plugins and/or themes).
+ *
+ * @access private
+ */
+class WP_Fonts_Resolver {
+	/**
+	 * Defines the key structure in global styles to the fontFamily
+	 * user-selected font.
+	 *
+	 * @since X.X.X
+	 *
+	 * @var string[][]
+	 */
+	protected static $global_styles_font_family_structure = array(
+		array( 'elements', 'link', 'typography', 'fontFamily' ),
+		array( 'elements', 'heading', 'typography', 'fontFamily' ),
+		array( 'elements', 'caption', 'typography', 'fontFamily' ),
+		array( 'elements', 'button', 'typography', 'fontFamily' ),
+		array( 'typography', 'fontFamily' ),
+	);
+
+	/**
+	 * Enqueues user-selected fonts via global styles.
+	 *
+	 * @since X.X.X
+	 *
+	 * @return array User selected font-families when exists, else empty array.
+	 */
+	public static function enqueue_user_selected_fonts() {
+		$global_styles       = wp_get_global_styles();
+		$user_selected_fonts = static::get_user_selected_fonts( $global_styles );
+		if ( empty( $user_selected_fonts ) ) {
+			return array();
+		}
+
+		wp_enqueue_fonts( $user_selected_fonts );
+		return $user_selected_fonts;
+	}
+
+	/**
+	 * Gets the user-selected font-family handles.
+	 *
+	 * @since X.X.X
+	 *
+	 * @param  array $global_styles Global styles potentially containing user-selected fonts.
+	 * @return array User-selected font-families.
+	 */
+	private static function get_user_selected_fonts( array $global_styles ) {
+		$font_families = array();
+
+		foreach ( static::$global_styles_font_family_structure as $path ) {
+			$style_value = _wp_array_get( $global_styles, $path, '' );
+
+			$font_family = static::get_value_from_style( $style_value );
+			if ( '' !== $font_family ) {
+				$font_families[] = $font_family;
+			}
+		}
+
+		return array_unique( $font_families );
+	}
+
+	/**
+	 * Get the value (i.e. preset slug) from the given style value.
+	 *
+	 * @since X.X.X
+	 *
+	 * @param string $style       The style to parse.
+	 * @param string $preset_type Optional. The type to parse. Default 'font-family'.
+	 * @return string Preset slug.
+	 */
+	private static function get_value_from_style( $style, $preset_type = 'font-family' ) {
+		if ( '' === $style ) {
+			return '';
+		}
+
+		$starting_pattern = "var:preset|{$preset_type}|";
+		if ( ! str_starts_with( $style, $starting_pattern ) ) {
+			return '';
+		}
+
+		return substr( $style, strlen( $starting_pattern ) );
+	}
+}

lib/experimental/fonts-api/fonts-api.php

@@ -198,19 +198,17 @@ function wp_print_fonts( $handles = false ) {
 			return array();
 		}
 
-		// Skip this reassignment decision-making when using the default of `false`.
-		if ( false !== $handles ) {
-			// When `true`, print all registered fonts for the iframed editor.
-			if ( $in_iframed_editor ) {
-				$queue           = $wp_fonts->queue;
-				$done            = $wp_fonts->done;
-				$wp_fonts->done  = array();
-				$wp_fonts->queue = $registered;
-				$handles         = false;
-			} elseif ( empty( $handles ) ) {
-				// When falsey, assign `false` to print enqueued fonts.
-				$handles = false;
-			}
+		if ( empty( $handles ) ) {
+			// Automatically enqueue all user-selected fonts.
+			WP_Fonts_Resolver::enqueue_user_selected_fonts();
+			$handles = false;
+		} elseif ( $in_iframed_editor ) {
+			// Print all registered fonts for the iframed editor.
+			$queue           = $wp_fonts->queue;
+			$done            = $wp_fonts->done;
+			$wp_fonts->done  = array();
+			$wp_fonts->queue = $registered;
+			$handles         = false;
 		}
 
 		_wp_scripts_maybe_doing_it_wrong( __FUNCTION__ );

lib/load.php

@@ -112,7 +112,9 @@ function gutenberg_is_experiment_enabled( $name ) {
 	require __DIR__ . '/experimental/fonts-api/register-fonts-from-theme-json.php';
 	require __DIR__ . '/experimental/fonts-api/class-wp-fonts.php';
 	require __DIR__ . '/experimental/fonts-api/class-wp-fonts-provider-local.php';
+	require __DIR__ . '/experimental/fonts-api/class-wp-fonts-resolver.php';
 	require __DIR__ . '/experimental/fonts-api/fonts-api.php';
+
 	// BC Layer files, which will not be backported to WP Core.
 	require __DIR__ . '/experimental/fonts-api/bc-layer/class-gutenberg-fonts-api-bc-layer.php';
 	require __DIR__ . '/experimental/fonts-api/bc-layer/webfonts-deprecations.php';