Plugins: Avoid stomping of some variables in wp-settings.php.

This changeset decreases the chance of accidentally overwriting some variables located in `wp-settings.php`, as the chance of overriding a variable called `$_wp_plugin_file` would be lower than for `$plugin`, `$mu_plugin` or `$network_plugin`.

Props stevegrunwell, joyously, peterwilsoncc, ocean90, SergeyBiryukov, jrf, azouamauriac.
Fixes #55432.

Built from https://develop.svn.wordpress.org/trunk@53004


git-svn-id: http://core.svn.wordpress.org/trunk@52593 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.0-alpha-53003';
+$wp_version = '6.0-alpha-53004';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.

wp-settings.php

@@ -346,7 +346,9 @@
 
 // Load must-use plugins.
 foreach ( wp_get_mu_plugins() as $mu_plugin ) {
+	$_wp_plugin_file = $mu_plugin;
 	include_once $mu_plugin;
+	$mu_plugin = $_wp_plugin_file; // Avoid stomping of the $mu_plugin variable in a plugin.
 
 	/**
 	 * Fires once a single must-use plugin has loaded.
@@ -357,13 +359,16 @@
 	 */
 	do_action( 'mu_plugin_loaded', $mu_plugin );
 }
-unset( $mu_plugin );
+unset( $mu_plugin, $_wp_plugin_file );
 
 // Load network activated plugins.
 if ( is_multisite() ) {
 	foreach ( wp_get_active_network_plugins() as $network_plugin ) {
 		wp_register_plugin_realpath( $network_plugin );
+
+		$_wp_plugin_file = $network_plugin;
 		include_once $network_plugin;
+		$network_plugin = $_wp_plugin_file; // Avoid stomping of the $network_plugin variable in a plugin.
 
 		/**
 		 * Fires once a single network-activated plugin has loaded.
@@ -374,7 +379,7 @@
 		 */
 		do_action( 'network_plugin_loaded', $network_plugin );
 	}
-	unset( $network_plugin );
+	unset( $network_plugin, $_wp_plugin_file );
 }
 
 /**
@@ -415,7 +420,10 @@
 // Load active plugins.
 foreach ( wp_get_active_and_valid_plugins() as $plugin ) {
 	wp_register_plugin_realpath( $plugin );
+
+	$_wp_plugin_file = $plugin;
 	include_once $plugin;
+	$plugin = $_wp_plugin_file; // Avoid stomping of the $plugin variable in a plugin.
 
 	/**
 	 * Fires once a single activated plugin has loaded.
@@ -426,7 +434,7 @@
 	 */
 	do_action( 'plugin_loaded', $plugin );
 }
-unset( $plugin );
+unset( $plugin, $_wp_plugin_file );
 
 // Load pluggable functions.
 require ABSPATH . WPINC . '/pluggable.php';