Code Modernization: Fix instances of using null as an array offset.

This avoids using multisite-specific tables and columns in `WP_Date_Query::validate_column()` when on a non-multisite install. Attempting to use `$wpdb->blogs` as an array index when `null` on a non-multisite install causes a deprecation notice in PHP 8.5. This also updates the multisite table alias in `wpdb` to make it clear they could be `null`.

Developed in #10498

Follow-up to [60904], [60809], [37477].

Props westonruter, desrosj.
See #63061.
Fixes #63957.


git-svn-id: https://develop.svn.wordpress.org/trunk@61191 602fd350-edb4-49c9-b593-d223f7449a82

Author: westonruter

src/wp-includes/class-wp-date-query.php

@@ -482,17 +482,25 @@ public function validate_column( $column ) {
 		global $wpdb;
 
 		$valid_columns = array(
-			'post_date',
-			'post_date_gmt',
-			'post_modified',
-			'post_modified_gmt',
-			'comment_date',
-			'comment_date_gmt',
-			'user_registered',
-			'registered',
-			'last_updated',
+			'post_date',         // Part of $wpdb->posts.
+			'post_date_gmt',     // Part of $wpdb->posts.
+			'post_modified',     // Part of $wpdb->posts.
+			'post_modified_gmt', // Part of $wpdb->posts.
+			'comment_date',      // Part of $wpdb->comments.
+			'comment_date_gmt',  // Part of $wpdb->comments.
+			'user_registered',   // Part of $wpdb->users.
 		);
 
+		if ( is_multisite() ) {
+			$valid_columns = array_merge(
+				$valid_columns,
+				array(
+					'registered',   // Part of $wpdb->blogs.
+					'last_updated', // Part of $wpdb->blogs.
+				)
+			);
+		}
+
 		// Attempt to detect a table prefix.
 		if ( ! str_contains( $column, '.' ) ) {
 			/**
@@ -525,11 +533,14 @@ public function validate_column( $column ) {
 				$wpdb->users    => array(
 					'user_registered',
 				),
-				$wpdb->blogs    => array(
+			);
+
+			if ( is_multisite() ) {
+				$known_columns[ $wpdb->blogs ] = array(
 					'registered',
 					'last_updated',
-				),
-			);
+				);
+			}
 
 			// If it's a known column name, add the appropriate table prefix.
 			foreach ( $known_columns as $table_name => $table_columns ) {

src/wp-includes/class-wpdb.php

@@ -467,7 +467,7 @@ class wpdb {
 	 *
 	 * @since 3.0.0
 	 *
-	 * @var string
+	 * @var string|null
 	 */
 	public $blogs;
 
@@ -476,7 +476,7 @@ class wpdb {
 	 *
 	 * @since 5.1.0
 	 *
-	 * @var string
+	 * @var string|null
 	 */
 	public $blogmeta;
 
@@ -485,7 +485,7 @@ class wpdb {
 	 *
 	 * @since 3.0.0
 	 *
-	 * @var string
+	 * @var string|null
 	 */
 	public $registration_log;
 
@@ -494,7 +494,7 @@ class wpdb {
 	 *
 	 * @since 3.0.0
 	 *
-	 * @var string
+	 * @var string|null
 	 */
 	public $signups;
 
@@ -503,7 +503,7 @@ class wpdb {
 	 *
 	 * @since 3.0.0
 	 *
-	 * @var string
+	 * @var string|null
 	 */
 	public $site;
 
@@ -512,7 +512,7 @@ class wpdb {
 	 *
 	 * @since 3.0.0
 	 *
-	 * @var string
+	 * @var string|null
 	 */
 	public $sitecategories;
 
@@ -521,7 +521,7 @@ class wpdb {
 	 *
 	 * @since 3.0.0
 	 *
-	 * @var string
+	 * @var string|null
 	 */
 	public $sitemeta;