wp-includes/class-wpdb.php:3854Loads the column metadata from the last query.
protected function load_col_info() { if ( $this->col_info ) { return; } $num_fields = mysqli_num_fields( $this->result ); for ( $i = 0; $i < $num_fields; $i++ ) { $this->col_info[ $i ] = mysqli_fetch_field( $this->result ); } }Introduced in 3.5.0. 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.