Source

File: wp-includes/comment.php

function wp_transition_comment_status( $new_status, $old_status, $comment ) {
	/*
	 * Translate raw statuses to human-readable formats for the hooks.
	 * This is not a complete list of comment status, it's only the ones
	 * that need to be renamed.
	 */
	$comment_statuses = array(
		0         => 'unapproved',
		'hold'    => 'unapproved', // wp_set_comment_status() uses "hold".
		1         => 'approved',
		'approve' => 'approved',   // wp_set_comment_status() uses "approve".
	);
	if ( isset( $comment_statuses[ $new_status ] ) ) {
		$new_status = $comment_statuses[ $new_status ];
	}
	if ( isset( $comment_statuses[ $old_status ] ) ) {
		$old_status = $comment_statuses[ $old_status ];
	}

	// Call the hooks.
	if ( $new_status != $old_status ) {
		/**
		 * Fires when the comment status is in transition.
		 *
		 * @since 2.7.0
		 *
		 * @param int|string $new_status The new comment status.
		 * @param int|string $old_status The old comment status.
		 * @param WP_Comment $comment    Comment object.
		 */
		do_action( 'transition_comment_status', $new_status, $old_status, $comment );
		/**
		 * Fires when the comment status is in transition from one specific status to another.
		 *
		 * The dynamic portions of the hook name, `$old_status`, and `$new_status`,
		 * refer to the old and new comment statuses, respectively.
		 *
		 * @since 2.7.0
		 *
		 * @param WP_Comment $comment Comment object.
		 */
		do_action( "comment_{$old_status}_to_{$new_status}", $comment );
	}
	/**
	 * Fires when the status of a specific comment type is in transition.
	 *
	 * The dynamic portions of the hook name, `$new_status`, and `$comment->comment_type`,
	 * refer to the new comment status, and the type of comment, respectively.
	 *
	 * Typical comment types include an empty string (standard comment), 'pingback',
	 * or 'trackback'.
	 *
	 * @since 2.7.0
	 *
	 * @param int        $comment_ID The comment ID.
	 * @param WP_Comment $comment    Comment object.
	 */
	do_action( "comment_{$new_status}_{$comment->comment_type}", $comment->comment_ID, $comment );
}