Deprecate and make Fonts API non-functional.

[hellofromtonya]

Closes 51819.

What?

Creates a BC Layer in the new Font Face.

Deprecates all of the Fonts API's public-facing files, functions, classes, and methods.

Makes the Fonts API non-functional, i.e. as Font Face replaces it.

Why?

Font Face replaces Fonts API.

For sites using the Fonts API, this PR:

1. Avoids those sites experiencing a fatal parsing error.
2. Makes the Fonts API non-functional to avoid conflicts with the new font management approach.

How?

1. Copies all of the Fonts API's files into a new fonts/bc-layer directory.
2. Removes all private methods.
3. Removes all functionality from remaining functions and methods.
4. Deprecates all of the files, classes, functions, and methods.
5. Loads the files into memory (to avoid fatal parsing errors on sites using it).

Testing Instructions

Set up

1. Enable the loading of the Font Face files:
   a. Open lib/load.php.
   b. Scroll down to where the Font Face files are loaded.
   c. Add true || in the if:

if ( true || class_exists( 'WP_Fonts_Library' ) || class_exists( 'WP_Fonts_Library_Controller' ) ) {

2. Plugin using the Fonts API:

• Install and activate this test plugin.
• Comment out these 3 lines of code in the webfonts.php file:

                 if ( ! function_exists( 'wp_register_font_provider' ) || ! function_exists( 'wp_register_fonts' ) ) {
                        return;
                }

Reproduce the fatal error

Before applying the changes from this PR (or comment out the BC Layer files loading in lib/load.php, refresh the admin page on your test site.

Expected: Fatal error such as:

Fatal error: Uncaught Error: Call to undefined function wp_register_font_provider() in ../wp-content/plugins/webfonts-jetpack-test/webfonts.php:79

the path to the webfonts.php will be different in your test site.

This fatal error happens because the tester plugin is using the Fonts API but it is not loaded into memory.

Test this PR

1. Apply the changes from this PR to your local testing site.
2. Refresh the admin page.
   Expected: No fatal error. There will be deprecation notices as the tester plugin is using the Fonts API (which is now deprecated).
3. Check that none of the Google Fonts from the tester plugin are in the font pickers:
   a. Go to Site Editor > Styles > Typography > Headings.
   b. Select "FONT".
   Expected: Google Fonts such as Arvo, Merriweather, Open Sans, etc. are not in the list. Rather, only the theme's fonts in the list.

Using TT3, the FONT picker should contain:

• Default
• DM Sans
• IBM Plex Mono
• Inter
• System Font
• Source Serif Pro
  

Note: To see all of the Google Fonts the tester plugin registers, remove the true so that the Font Face libs are not loaded.

[anton-vlasenko]

Test Report

PR tested: #52485

Environment

• WordPress: 6.3-beta3-56130-src
• PHP: 8.0.27
• Server: Apache/2.4.55 (Unix) PHP/8.0.27
• Database: mysqli (Server: 5.7.38 / Client: mysqlnd 8.0.27)
• Browser: Safari 16.5 (macOS)
• Theme: Twenty Twenty-Three 1.1
• MU-Plugins: None activated
• Plugins:
  • Fonts API Test Plugin 1.0.0-ironprogrammer
  • Gutenberg 16.2.0-rc.1

Steps to Test

Follow the steps listed in the PR's description above.

Expected Results

1. Fatal error

Uncaught Error: Class 'WP_Fonts_Resolver' not found

occurs before applying the changes from this PR.
2. The font picker should contain the expected fonts.

Actual Results

1. ❌ Fatal error Uncaught Error: Class 'WP_Fonts_Resolver' not found doesn't occur whether using the trunk branch or commenting out the BC layer files loading in load.php.
2. ✅ The font picker contains the expected fonts.

Supplemental Artifacts

[anton-vlasenko]

The code LGTM.
However, I'm not sure why the fatal error doesn't occur when the BC layer files are not loaded. Please see my test report here: #52485 (comment).

[aristath]

Code LGTM 👍

[hellofromtonya]

The code LGTM.
However, I'm not sure why the fatal error doesn't occur when the BC layer files are not loaded. Please see my test report here: #52485 (comment).

Oh silly me 🤦‍♀️ Thanks @anton-vlasenko for flagging this. I missed a step in the Set up process and the fatal error is a different one.

I've updated the testing instructions. The tester plugin already guards against the functions not existing. By commenting out those lines of code, a fatal error will happen when it attempts to invoke wp_register_font_provider() when it does not exist in memory.

[anton-vlasenko]

I've updated the testing instructions. The tester plugin already guards against the functions not existing. By commenting out those lines of code, a fatal error will happen when it attempts to invoke wp_register_font_provider() when it does not exist in memory.

Thank you, @hellofromtonya. I'm able to reproduce the fatal error now.

[anton-vlasenko]

LGTM ✅.

[hellofromtonya]

Thank you @aristath and @anton-vlasenko 🎉 Merging now.

[hellofromtonya]

Removed Needs PHP backport label as this PR will not be backported to Core. The Fonts API is deprecated within the plugin.