Make devicepx library an optional theme feature

3rd-party/class.jetpack-amp-support.php

@@ -12,6 +12,12 @@ static function init() {
 			return;
 		}
 
+		/**
+		 * Remove this during the init hook in case users have enabled it during
+		 * the after_setup_theme hook, which triggers before init.
+		 */
+		remove_theme_support( 'jetpack-devicepx' );
+
 		// enable stats
 		if ( Jetpack::is_module_active( 'stats' ) ) {
 			add_action( 'amp_post_template_footer', array( 'Jetpack_AMP_Support', 'add_stats_pixel' ) );

class.jetpack.php

@@ -628,9 +628,6 @@ private function __construct() {
 		add_action( 'wp_ajax_jetpack_connection_banner', array( $this, 'jetpack_connection_banner_callback' ) );
 
 		add_action( 'wp_loaded', array( $this, 'register_assets' ) );
-		add_action( 'wp_enqueue_scripts', array( $this, 'devicepx' ) );
-		add_action( 'customize_controls_enqueue_scripts', array( $this, 'devicepx' ) );
-		add_action( 'admin_enqueue_scripts', array( $this, 'devicepx' ) );
 
 		// gutenberg locale
 		add_action( 'enqueue_block_editor_assets', array( $this, 'enqueue_gutenberg_locale' ) );
@@ -1096,16 +1093,6 @@ function get_locale() {
 		return $locale;
 	}
 
-	/**
-	 * Device Pixels support
-	 * This improves the resolution of gravatars and wordpress.com uploads on hi-res and zoomed browsers.
-	 */
-	function devicepx() {
-		if ( Jetpack::is_active() && ! Jetpack_AMP_Support::is_amp_request() ) {
-			wp_enqueue_script( 'devicepx', 'https://s0.wp.com/wp-content/js/devicepx-jetpack.js', array(), gmdate( 'oW' ), true );
-		}
-	}
-
 	/**
 	 * Return the network_site_url so that .com knows what network this site is a part of.
 	 * @param  bool $option

modules/module-extras.php

@@ -15,6 +15,7 @@
 	'theme-tools/site-breadcrumbs.php',
 	'theme-tools/social-menu.php',
 	'theme-tools/content-options.php',
+	'theme-tools/devicepx.php',
 	'custom-post-types/comics.php',
 	'custom-post-types/testimonial.php',
 	'custom-post-types/nova.php',

modules/theme-tools/devicepx.php

@@ -0,0 +1,35 @@
+<?php
+/**
+ * Loads the devicepx library which improves the resolution of gravatars and
+ * wordpress.com uploads on hi-res and zoomed browsers.
+ *
+ * This feature will only be activated for themes that declare their support.
+ * This can be done by adding code similar to the following during the
+ * 'after_setup_theme' action:
+ *
+ * add_theme_support( 'jetpack-devicepx' );
+ */
+
+/**
+ * Add hooks to enqueue the devicepx JS library, if enabled. The feature must
+ * be enabled earlier during `after_setup_theme`.
+ *
+ * @uses current_theme_supports, add_action, Jetpack::is_active
+ */
+function jetpack_devicepx_init() {
+	if ( Jetpack::is_active() && current_theme_supports( 'jetpack-devicepx' ) ) {
+		add_action( 'wp_enqueue_scripts', 'jetpack_devicepx_enqueue' );
+		add_action( 'customize_controls_enqueue_scripts', 'jetpack_devicepx_enqueue' );
+		add_action( 'admin_enqueue_scripts', 'jetpack_devicepx_enqueue' );
+	}
+}
+add_action( 'init', 'jetpack_devicepx_init', 99 );
+
+/**
+ * Enqueue the devicepx JS library.
+ *
+ * @uses wp_enqueue_script
+ */
+function jetpack_devicepx_enqueue() {
+	wp_enqueue_script( 'devicepx', 'https://s0.wp.com/wp-content/js/devicepx-jetpack.js', array(), gmdate( 'oW' ), true );
+}

phpunit.xml.dist

@@ -76,6 +76,9 @@
 		<testsuite name="sync">
 			<directory prefix="test_" suffix=".php">tests/php/sync</directory>
 		</testsuite>
+		<testsuite name="theme-tools">
+			<directory prefix="test_" suffix=".php">php/modules/theme-tools</directory>
+		</testsuite>
 		<testsuite name="uninstall">
 			<directory prefix="test_" suffix=".php">tests/php/uninstall</directory>
 		</testsuite>

tests/php.multisite.xml

@@ -60,6 +60,9 @@
         <testsuite name="sync">
             <directory prefix="test_" suffix=".php">php/sync</directory>
         </testsuite>
+        <testsuite name="theme-tools">
+            <directory prefix="test_" suffix=".php">php/modules/theme-tools</directory>
+        </testsuite>
         <testsuite name="uninstall">
             <directory prefix="test_" suffix=".php">php/uninstall</directory>
         </testsuite>

tests/php/modules/theme-tools/test_functions.devicepx.php

@@ -0,0 +1,33 @@
+<?php
+
+require_once JETPACK__PLUGIN_DIR . '/modules/theme-tools/devicepx.php';
+
+/**
+ * @covers jetpack_devicepx_init
+ */
+function test_devicepx_not_enqueued_by_default() {
+	$this->assertFalse( current_theme_supports( 'jetpack-devicepx' ) );
+}
+
+/**
+ * @covers jetpack_devicepx_init
+ */
+function test_devicepx_can_be_enabled() {
+	// Enable the feature.
+	add_theme_supports( 'jetpack-devicepx' );
+
+	$this->assertTrue(
+		current_theme_supports( 'jetpack-devicepx' ),
+		'Themes do not support devicepx by default'
+	);
+
+	jetpack_devicepx_init();
+
+	$this->assertTrue(
+		wp_script_is( 'jetpack-devicepx', 'enqueued' ),
+		'devicepx script has been enquued'
+	);
+
+	// Remove to not mess with other tests.
+	remove_theme_supports( 'jetpack-devicepx' );
+}