The static instance of `WP_Font_Face` is not needed. It was an unnecessary carryover from the experimental Fonts API (which was not introduced into Core).
Whereas the Fonts API needed to persist its data (i.e. to maintain the registered and enqueued fonts throughout the web request), Font Face does not have data to persist.
Font Face processes the fonts it receives when `WP_Font_Face::generate_and_print( $fonts )` is invoked. Thus, a singleton is not needed.
Removing the static reduces the amount of the code in the function and eliminates running its tests in separate processes to ensure a different instance is always used.
References:
* [https://github.com/WordPress/gutenberg/pull/54228 Gutenberg PR 54228].
Follow-up to [56500].
Props hellofromTonya, costdev.
Fixes#59165.
Built from https://develop.svn.wordpress.org/trunk@56540
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Introducing Font Face, a server-side `@font-face` styles generator and printer.
tl;dr:
* Introduces Font Face.
* Deprecates `_wp_theme_json_webfonts_handler()`.
**Introduce Font Face**
From an array of fonts (i.e. each font-family and its font variations to be processed), it:
1. Validates each `font-face` declaration, i.e. the CSS property and value pairing. If validation fails, processing stops with no font-face styles printed.
3. Generates the `@font-face` CSS for each font-family.
4. Prints the CSS within a `<style id="wp-fonts-local">` element.
The entry point into Font Face is through a new global function called `wp_print_font_faces()`, which is automatically called:
* when the `'wp_head'` hook runs (for the front-end).
* when the `'admin_print_styles'` hook runs (for the back-end).
* when `_wp_get_iframed_editor_assets()` runs to inject the `@font-face` styles into the iframed editor.
Once called, it gets the fonts from Theme_JSON merged data layer, which includes theme defined fonts and user activated fonts (once the Font Library #59166 is introduced into Core).
For classic sites, themes and plugins can directly call `wp_print_font_faces()` and pass their fonts array to it for processing.
**Deprecates `_wp_theme_json_webfonts_handler()`.**
As Font Face is a direct replacement, the stopgap code in `_wp_theme_json_webfonts_handler()` (introduced in 6.0.0 via [53282]) is deprecated and unused in Core.
**Props note:**
There's a long multiple year history baked into Font Face, which dates back to the early versions of a web font API (see #46370 and [https://github.com/WordPress/gutenberg/issues/41479 roadmap]. The props list includes those who contributed from those early versions up to this commit.
**References:**
* #46370 original (Web)Fonts API proposal for registering and enqueuing web fonts.
* [https://github.com/WordPress/gutenberg/issues/41479 Gutenberg tracking issue] which includes the evolution from Webfonts API to Fonts API to Font Face.
* [53282] / #55567 Added the stopgap code `_wp_theme_json_webfonts_handler()` in 6.0.
* [https://developer.mozilla.org/en-US/docs/Web/CSS/@font-face @font-face on mdn web docs]
* #59166 Font Library: Font manager for WordPress
Follow-up to [53282].
Props aristath, jonoaldersonwp, hellofromTonya, andraganescu, annezazu, antonvlasenko, arena, askdesign, azaozz, bph, bradley2083, colorful-tones, costdev, davidbaumwald, desrosj, dingo_d, djcowan, domainsupport, dryanpress, elmastudio, flixos90, francina, garrett-eclipse, gigitux, grantmkin, grapplerulrich, gziolo, ironprogrammer, jb510, jeffpaul, jeremyyip, jffng, joostdevalk, jorgefilipecosta, juanmaguitar, mamaduka, matveb, mburridge, mitogh, ndiego, ntsekouras, oandregal, ocean90, oglekler, paaljoachim, pagelab, peterwilsoncc, poena, priethor, scruffian, SergeyBiryukov, shiloey, simison, skorasaurus, soean, westonruter, wildworks, zaguiini.
Fixes#59165.
Built from https://develop.svn.wordpress.org/trunk@56500
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