Add upstream

wp-content/plugins/jetpack/require-lib.php

@@ -0,0 +1,36 @@
+<?php
+function jetpack_require_lib( $slug ) {
+	if ( !preg_match( '|^[a-z0-9/_.-]+$|i', $slug ) ) {
+		trigger_error( "Cannot load a library with invalid slug $slug.", E_USER_ERROR );
+		return;
+	}
+	$basename = basename( $slug );
+
+	if ( defined( 'ABSPATH' ) && ! defined( 'WP_CONTENT_DIR' ) ) {
+		define( 'WP_CONTENT_DIR', ABSPATH . 'wp-content' ); // no trailing slash, full paths only - WP_CONTENT_URL is defined further down
+	}
+
+	$lib_dir = WP_CONTENT_DIR . '/lib';
+
+	/**
+	 * Filter the location of the library directory.
+	 *
+	 * @since 2.5.0
+	 *
+	 * @param string $lib_dir Path to the library directory.
+	 */
+	$lib_dir = apply_filters( 'jetpack_require_lib_dir', $lib_dir );
+	$choices = array(
+		JETPACK__PLUGIN_DIR . "vendor/automattic/jetpack-compat/lib/$slug.php",
+		"$lib_dir/$slug.php",
+		"$lib_dir/$slug/0-load.php",
+		"$lib_dir/$slug/$basename.php",
+	);
+	foreach( $choices as $file_name ) {
+		if ( is_readable( $file_name ) ) {
+			require_once $file_name;
+			return;
+		}
+	}
+	trigger_error( "Cannot find a library with slug $slug.", E_USER_ERROR );
+}