https://meta.trac.wordpress.org/ticket/762 - https://meta.trac.wordpress.org/ticket/960

site-themes.php

<?php

class Dotorg_Theme_Review_Assigner {

	protected $trac;

	function __construct() {
		add_action( 'widgets_init', array( $this, 'widgets_init' ) );
		add_action( 'init', array( $this, 'shortcode_init' ) );
		add_action( 'admin_post_assign_theme_review', array( $this, 'admin_post' ) );
	}

	function require_trac() {
		require_once ABSPATH . WPINC . '/class-IXR.php';
		require_once ABSPATH . WPINC . '/class-wp-http-ixr-client.php';
		require_once WPORGPATH . 'bb-theme/themes/lib/class-trac.php';
		$this->trac = new Trac( 'themetracbot', THEME_TRACBOT_PASSWORD, 'https://themes.trac.wordpress.org/login/xmlrpc' );
	}

	function widgets_init() {
		register_widget( 'Dotorg_Theme_Review_Widget' );
	}

	function shortcode_init() {
		add_shortcode( 'assign-theme-review', array( $this, 'assign_button' ) );
	}

	function assign_button() {
		$action = isset( $_GET['theme-assign'] ) ? $_GET['theme-assign'] : false;

		if ( $action && $_GET['now'] < time() - 10 ) {
			// If the page was refreshed > 10 seconds later, ignore the action and show the button again.
			$action = false;
		}

		if ( 'existing' === $action ) {
			$button = sprintf( '<p><strong>You have reviews <a href="%s">assigned to you</a> that you need to complete first.</strong></p>',
				esc_url( 'https://themes.trac.wordpress.org/query?status=!closed&owner=$USER' ) );
		} elseif ( 'none' === $action ) {
			$button =  '<p><strong>There are no themes in the review queue to assign right now. Check back soon.</strong></p>';
		} elseif ( 'failed' === $action ) {
			$button =  '<p><strong>Something went wrong; the system can&#8127;t assign you a review right now.</strong></p>';
		} elseif ( is_user_logged_in() ) {
			$url = add_query_arg( '_wp_get_referer', $_SERVER['REQUEST_URI'], admin_url( 'admin-post.php?action=assign_theme_review' ) );
			$url = wp_nonce_url( $url, 'assign-theme-review' );
			$button = sprintf( '<p><form method="post" action="%s"><button>Request a theme to review</button></form></p>', esc_url( $url ) );
		} else {
			$button = sprintf( '<p>Please <a href="%s">log in</a> first to review.</em></p>', esc_url( wp_login_url( $_SERVER['REQUEST_URI'] ) ) );
		}
		return $button;
	}

	function admin_post() {
		check_admin_referer( 'assign-theme-review' );

		$this->require_trac();

		$assignments = $this->get_current_assignments();
		if ( is_wp_error( $assignments ) ) {
			$result = 'failed';
		} elseif ( $assignments ) {
			$result = 'existing';
		} else {
			$ticket = $this->assign_next_theme();
			if ( is_wp_error( $ticket ) ) {
				$result = 'failed';
			} elseif ( $ticket ) {
				$result = $ticket;
			} else {
				$result = 'none';
			}
		}

		if ( is_int( $result ) ) {
			wp_redirect( 'https://themes.trac.wordpress.org/ticket/' . $result );
			exit;
		}

		$redirect = add_query_arg( array( 'theme-assign' => $result, 'now' => time() ), wp_get_referer() );
		wp_safe_redirect( $redirect );
		exit;
	}

	function get_current_assignments() {
		$username = wp_get_current_user()->user_login;
		$assigned = $this->trac->ticket_query( sprintf( 'owner=%s&status=reviewing', $username ) );
		if ( $assigned ) {
			return $assigned;
		} elseif ( $assigned === array() ) {
			return false;
		} else {
			// RPC failure condition ($assigned is false here)
			return new WP_Error;
		}
	}

	function assign_next_theme() {
		$username = wp_get_current_user()->user_login;
		$assigned = false;
		$i = 0;
		do {
			if ( ++$i > 10 ) {
				// Safeguard.
				return new WP_Error;
			}

			$next_ticket = $this->trac->ticket_query( 'priority=new theme&priority=previously reviewed&status=new&keywords=!~buddypress&order=time&max=1&owner=' );
			if ( $next_ticket === array() ) {
				return false;
			} elseif ( $next_ticket === false ) {
				return new WP_Error;
			}

			$ticket = $this->trac->ticket_get( $next_ticket[0] );
			// Avoid race condition: Maybe someone was just assigned this one between query and get.
			if ( $ticket['owner'] || $ticket['status'] !== 'new' ) {
				continue;
			}

			// Assign the ticket using the proper workflow actions.
			$attributes = array( 'action' => 'review_other', 'action_review_other_reassign_owner' => $username );

			// Set _ts (changetime) so the update will fail if the ticket was updated since our fetch.
			$attributes['_ts'] = $ticket['_ts'];

			// No comment, yes notify. User is 'themetracbot'.
			$updated = $this->trac->ticket_update( $ticket['id'], '', $attributes, true );
			if ( ! $updated ) {
				// Update failed. Try another ticket.
				continue;
			}

			$assigned = (int) $ticket['id'];
		} while ( ! $assigned );
		return $assigned;
	}
}

// Hack so this can sit in a mu-plugin (included before widgets are)
add_action( 'widgets_init', function() {

class Dotorg_Theme_Review_Widget extends WP_Widget_Text {
	function __construct() {
		$widget_ops = array( 'classname' => 'dotorg_theme_review_widget', 'description' => 'Widget for theme reviewers to self-assign themselves themes.' );
		$control_ops = array( 'width' => 400, 'height' => 350 );
		WP_Widget::__construct('dotorg_theme_review', __('Theme Review Self-Assign'), $widget_ops, $control_ops );
	}

	function widget( $args, $instance ) {
		ob_start();
		echo '<style>
			.dotorg_theme_review_widget .textwidget { font-size: 14px; color: #333 }
			.dotorg_theme_review_widget .textwidget p { margin: 1em 0; }
			.dotorg_theme_review_widget button { font-size: 13px; }
			</style>';
		$action = isset( $_GET['theme-assign'] ) ? $_GET['theme-assign'] : false;

		if ( $action && $_GET['now'] < time() - 10 ) {
			// If the page was refreshed > 10 seconds later, ignore the action and show the button again.
			$action = false;
		}

		if ( 'existing' === $action ) {
			printf( '<p><strong>You have reviews <a href="%s">assigned to you</a> that you need to complete first.</strong></p>',
				esc_url( 'https://themes.trac.wordpress.org/query?status=!closed&owner=$USER' ) );
		} elseif ( 'none' === $action ) {
			echo '<p><strong>There are no themes in the review queue to assign right now. Check back soon.</strong></p>';
		} elseif ( 'failed' === $action ) {
			echo '<p><strong>Something went wrong; the system can&#8127;t assign you a review right now.</strong></p>';
		} elseif ( is_user_logged_in() ) {
			$url = add_query_arg( '_wp_get_referer', $_SERVER['REQUEST_URI'], admin_url( 'admin-post.php?action=assign_theme_review' ) );
			$url = wp_nonce_url( $url, 'assign-theme-review' );
			printf( '<p><form method="post" action="%s"><button>Request a theme to review</button></form></p>', esc_url( $url ) );
		} else {
			printf( '<p>Please <a href="%s">log in</a> first to review.</em></p>', esc_url( wp_login_url( $_SERVER['REQUEST_URI'] ) ) );
		}
		$instance['text'] .= ob_get_clean();
		parent::widget( $args, $instance );
	}
}

}, 9 );

new Dotorg_Theme_Review_Assigner( $themes_trac );