Font Face: to generate and print font-face styles for theme.json fonts (

#51770)

Introduces Font Face for generating and printing @font-face styles for fonts in theme.json merged data.

It's minimalistic in what it publicly exposes to avoid BC concerns.

There's no register, deregister, or enqueue of fonts or providers.

The fonts to be processed come directly from theme.json merged data which contains the theme's defined fonts and user "activated" fonts (from the Font Library).

This PR only loads Font Face into memory (thus replacing Fonts API) when the Fonts Library class. This design is intentional to ensure sites using Fonts API  stay functioning until Fonts Library is introduced. 
---------

Co-authored-by: Anton Vlasenko <vlasenko.anton@gmail.com>
Co-authored-by: Ari Stathopoulos <aristath@gmail.com>

lib/class-wp-theme-json-resolver-gutenberg.php

@@ -275,7 +275,9 @@ public static function get_theme_data( $deprecated = array(), $options = array()
 			}
 
 			// BEGIN OF EXPERIMENTAL CODE. Not to backport to core.
-			static::$theme = WP_Fonts_Resolver::add_missing_fonts_to_theme_json( static::$theme );
+			if ( ! class_exists( 'WP_Font_Face' ) && class_exists( 'WP_Fonts_Resolver' ) ) {
+				static::$theme = WP_Fonts_Resolver::add_missing_fonts_to_theme_json( static::$theme );
+			}
 			// END OF EXPERIMENTAL CODE.
 
 		}

lib/compat/wordpress-6.3/script-loader.php

@@ -81,7 +81,6 @@ function _gutenberg_get_iframed_editor_assets() {
 
 	ob_start();
 	wp_print_styles();
-	wp_print_fonts( true );
 	$styles = ob_get_clean();
 
 	ob_start();

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

@@ -243,3 +243,17 @@ static function( $mime_types ) {
  * during the build. See: tools/webpack/blocks.js.
  */
 add_action( 'init', 'WP_Fonts_Resolver::register_fonts_from_theme_json', 21 );
+
+add_filter(
+	'block_editor_settings_all',
+	static function( $settings ) {
+		ob_start();
+		wp_print_fonts( true );
+		$styles = ob_get_clean();
+
+		// Add the font-face styles to iframed editor assets.
+		$settings['__unstableResolvedAssets']['styles'] .= $styles;
+		return $settings;
+	},
+	11
+);

lib/experimental/fonts/class-wp-font-face-resolver.php

@@ -0,0 +1,158 @@
+<?php
+/**
+ * WP_Font_Face_Resolver class.
+ *
+ * @package    WordPress
+ * @subpackage Fonts
+ * @since      X.X.X
+ */
+
+if ( class_exists( 'WP_Font_Face_Resolver' ) ) {
+	return;
+}
+
+/**
+ * The Font Face Resolver abstracts the processing of different data sources
+ * (such as theme.json) for processing within the Font Face.
+ *
+ * This class is for internal core usage and is not supposed to be used by
+ * extenders (plugins and/or themes).
+ *
+ * @access private
+ */
+class WP_Font_Face_Resolver {
+
+	/**
+	 * Gets fonts defined in theme.json.
+	 *
+	 * @since X.X.X
+	 *
+	 * @return array Returns the font-families, each with their font-face variations.
+	 */
+	public static function get_fonts_from_theme_json() {
+		$settings = WP_Theme_JSON_Resolver_Gutenberg::get_merged_data()->get_settings();
+
+		// Bail out early if there are no font settings.
+		if ( empty( $settings['typography'] ) || empty( $settings['typography']['fontFamilies'] ) ) {
+			return array();
+		}
+
+		return static::parse_settings( $settings );
+	}
+
+	/**
+	 * Parse theme.json settings to extract font definitions with variations grouped by font-family.
+	 *
+	 * @since X.X.X
+	 *
+	 * @param array $settings Font settings to parse.
+	 * @return array Returns an array of fonts, grouped by font-family.
+	 */
+	private static function parse_settings( array $settings ) {
+		$fonts = array();
+
+		foreach ( $settings['typography']['fontFamilies'] as $font_families ) {
+			foreach ( $font_families as $definition ) {
+
+				// Skip if font-family "name" is not defined.
+				if ( empty( $definition['name'] ) ) {
+					continue;
+				}
+
+				// Skip if "fontFace" is not defined, meaning there are no variations.
+				if ( empty( $definition['fontFace'] ) ) {
+					continue;
+				}
+
+				$font_family = $definition['name'];
+
+				// Prepare the fonts array structure for this font-family.
+				if ( ! array_key_exists( $font_family, $fonts ) ) {
+					$fonts[ $font_family ] = array();
+				}
+
+				$fonts[ $font_family ] = static::convert_font_face_properties( $definition['fontFace'], $font_family );
+			}
+		}
+
+		return $fonts;
+	}
+
+	/**
+	 * Converts font-face properties from theme.json format.
+	 *
+	 * @since X.X.X
+	 *
+	 * @param array  $font_face_definition The font-face definitions to convert.
+	 * @param string $font_family_property The value to store in the font-face font-family property.
+	 * @return array Converted font-face properties.
+	 */
+	private static function convert_font_face_properties( array $font_face_definition, $font_family_property ) {
+		$converted_font_faces = array();
+
+		foreach ( $font_face_definition as $font_face ) {
+			// Add the font-family property to the font-face.
+			$font_face['font-family'] = $font_family_property;
+
+			// Converts the "file:./" src placeholder into a theme font file URI.
+			if ( ! empty( $font_face['src'] ) ) {
+				$font_face['src'] = static::to_theme_file_uri( (array) $font_face['src'] );
+			}
+
+			// Convert camelCase properties into kebab-case.
+			$font_face = static::to_kebab_case( $font_face );
+
+			$converted_font_faces[] = $font_face;
+		}
+
+		return $converted_font_faces;
+	}
+
+	/**
+	 * Converts each 'file:./' placeholder into a URI to the font file in the theme.
+	 *
+	 * The 'file:./' is specified in the theme's `theme.json` as a placeholder to be
+	 * replaced with the URI to the font file's location in the theme. When a "src"
+	 * beings with this placeholder, it is replaced, converting the src into a URI.
+	 *
+	 * @since X.X.X
+	 *
+	 * @param array $src An array of font file sources to process.
+	 * @return array An array of font file src URI(s).
+	 */
+	private static function to_theme_file_uri( array $src ) {
+		$placeholder = 'file:./';
+
+		foreach ( $src as $src_key => $src_url ) {
+			// Skip if the src doesn't start with the placeholder, as there's nothing to replace.
+			if ( ! str_starts_with( $src_url, $placeholder ) ) {
+				continue;
+			}
+
+			$src_file        = str_replace( $placeholder, '', $src_url );
+			$src[ $src_key ] = get_theme_file_uri( $src_file );
+		}
+
+		return $src;
+	}
+
+	/**
+	 * Converts all first dimension keys into kebab-case.
+	 *
+	 * @since X.X.X
+	 *
+	 * @param array $data The array to process.
+	 * @return array Data with first dimension keys converted into kebab-case.
+	 */
+	private static function to_kebab_case( array $data ) {
+		foreach ( $data as $key => $value ) {
+			$kebab_case          = _wp_to_kebab_case( $key );
+			$data[ $kebab_case ] = $value;
+			if ( $kebab_case !== $key ) {
+				unset( $data[ $key ] );
+			}
+		}
+
+		return $data;
+	}
+}