Source

File: wp-includes/class-wp-query.php

public function the_comment() {
		global $comment;

		$comment = $this->next_comment();

		if ( 0 == $this->current_comment ) {
			/**
			 * Fires once the comment loop is started.
			 *
			 * @since 2.2.0
			 */
			do_action( 'comment_loop_start' );
		}
	}