Add user-friendly version check to bootstrap file

Most of the plugin uses syntax from PHP 7.1, so this is the minimum version. Provide a version check, admin notice and self-deactivation if the site is running an earlier version of PHP.

The syntax in the main plugin file should be compatible with PHP 5.2.4, so that on attempted activation / update, it doesn't give a White Screen if the site is running on less than the required PHP version. The rest of the plugin initialisation is moved to `init.php`.

Author: GaryJones

genesis-js-no-js.php

@@ -1,14 +1,16 @@
 <?php
 /**
- * Genesis js / no-js WordPress plugin
+ * Genesis JS / No JS WordPress plugin
  *
  * For child themes of the Genesis Framework.
  *
- * Adds a no-js body class to the front-end, and a script on genesis_before
+ * Adds a no-js body class to the front end, and a script on genesis_before
  * which immediately changes the class to js if JavaScript is enabled. This is
- * how WP does things on the back-end, to allow different styles for the same
+ * how WP does things on the back end, to allow different styles for the same
  * elements depending if JavaScript is active or not.
  *
+ * This file should only use syntax available in PHP 5.2.4 or later.
+ *
  * @package   Gamajo\GenesisJsNoJs
  * @author    Gary Jones
  * @copyright 2011 Gary Jones, Gamajo
@@ -26,16 +28,50 @@
  * License URI:       http://www.gnu.org/licenses/gpl-2.0.txt
  * GitHub Plugin URI: https://github.com/GaryJones/genesis-js-no-js
  * GitHub Branch:     master
+ * Requires PHP:      7.1
+ * Requires WP:       4.6
  */
 
+// If this file is called directly, abort.
+if ( ! defined( 'WPINC' ) ) {
+	die;
+}
+
 if ( version_compare( PHP_VERSION, '7.1', '<' ) ) {
+	if ( current_user_can( 'activate_plugins' ) ) {
+		add_action( 'admin_init', 'plugin_slug_deactivate' );
+		add_action( 'admin_notices', 'plugin_slug_deactivation_notice' );
+
+		/**
+		 * Deactivate the plugin.
+		 */
+		function plugin_slug_deactivate() {
+			deactivate_plugins( plugin_basename( __FILE__ ) );
+		}
+
+		/**
+		 * Show deactivation admin notice.
+		 */
+		function plugin_slug_deactivation_notice() {
+			$notice = sprintf(
+				// Translators: 1: Required PHP version, 2: Current PHP version.
+				'<strong>Plugin name</strong> requires PHP %1$s to run. This site uses %2$s, so the plugin has been <strong>deactivated</strong>.',
+				'7.1',
+				PHP_VERSION
+			);
+			?>
+			<div class="updated"><p><?php echo wp_kses_post( $notice ); ?></p></div>
+			<?php
+			if ( isset( $_GET['activate'] ) ) { // WPCS: input var okay, CSRF okay.
+				unset( $_GET['activate'] ); // WPCS: input var okay.
+			}
+		}
+	}
+
 	return false;
 }
 
 /**
- * Load include files.
+ * Load plugin initialisation file.
  */
-require __DIR__ . '/src/GenesisJsNoJs.php';
-
-$genesis_js_no_js = new Gamajo\GenesisJsNoJs\GenesisJsNoJs();
-$genesis_js_no_js->run();
+require plugin_dir_path( __FILE__ ) . '/init.php';

init.php

@@ -0,0 +1,28 @@
+<?php
+/**
+ * Initialise the plugin
+ *
+ * This file can use syntax from the required level of PHP or later.
+ *
+ * @package   Gamajo\GenesisJsNoJs
+ * @author    Gary Jones
+ * @copyright 2011 Gary Jones, Gamajo
+ * @license   GPL-2.0+
+ */
+
+declare( strict_types = 1 );
+
+namespace Gamajo\GenesisJsNoJs;
+
+// If this file is called directly, abort.
+if ( ! defined( 'WPINC' ) ) {
+	die;
+}
+
+/**
+ * Load src files.
+ */
+require __DIR__ . '/src/GenesisJsNoJs.php';
+
+$genesis_js_no_js = new GenesisJsNoJs();
+$genesis_js_no_js->run();