wp-includes/class-wpdb.php:882Determines the best charset and collation to use given a charset and collation.
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public function determine_charset( $charset, $collate ) { if ( ( ! ( $this->dbh instanceof mysqli ) ) || empty( $this->dbh ) ) { return compact( 'charset', 'collate' ); } if ( 'utf8' === $charset ) { $charset = 'utf8mb4'; } if ( 'utf8mb4' === $charset ) { // _general_ is outdated, so we can upgrade it to _unicode_, instead. if ( ! $collate || 'utf8_general_ci' === $collate ) { $collate = 'utf8mb4_unicode_ci'; } else { $collate = str_replace( 'utf8_', 'utf8mb4_', $collate ); } } // _unicode_520_ is a better collation, we should use that when it's available. if ( $this->has_cap( 'utf8mb4_520' ) && 'utf8mb4_unicode_ci' === $collate ) { $collate = 'utf8mb4_unicode_520_ci'; } return compact( 'charset', 'collate' ); }Introduced in 4.6.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/class-wpdb.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.