WPDB: When we check the character set of a column, and find that it's `utf8mb4`, we should also check that the current connection supports `utf8mb4`. It's possible that the environment may have changed since upgrading the DB, so we can fall back to `utf8` when that happens.

Fixes #31771.


Built from https://develop.svn.wordpress.org/trunk@31947


git-svn-id: http://core.svn.wordpress.org/trunk@31926 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.2-beta3-31946';
+$wp_version = '4.2-beta3-31947';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.

wp-includes/wp-db.php

@@ -2219,6 +2219,12 @@ class wpdb {
 		foreach ( $columns as $column ) {
 			if ( ! empty( $column->Collation ) ) {
 				list( $charset ) = explode( '_', $column->Collation );
+
+				// If the current connection can't support utf8mb4 characters, let's only send 3-byte utf8 characters.
+				if ( 'utf8mb4' === $charset && ! $this->has_cap( 'utf8mb4' ) ) {
+					$charset = 'utf8';
+				}
+
 				$charsets[ strtolower( $charset ) ] = true;
 			}