Wordpress - In Gutenberg, now that withAPIData is being deprecated, how can I do an async call to a custom endpoint?

It's worth noting that the answer above is out of date. The data store should now look like this:

const actions = {
    setUserRoles( userRoles ) {
        return {
            type: 'SET_USER_ROLES',
            userRoles,
        };
    },
    receiveUserRoles( path ) {
        return {
            type: 'RECEIVE_USER_ROLES',
            path,
        };
    },
};

const store = registerStore( 'matt-watson/secure-block', {
    reducer( state = { userRoles: {} }, action ) {

        switch ( action.type ) {
            case 'SET_USER_ROLES':
                return {
                    ...state,
                    userRoles: action.userRoles,
                };
        }

        return state;
    },

    actions,

    selectors: {
        receiveUserRoles( state ) {
            const { userRoles } = state;
            return userRoles;
        },
    },

    controls: {
        RECEIVE_USER_ROLES( action ) {
            return apiFetch( { path: action.path } );
        },
    },

    resolvers: {
        * receiveUserRoles( state ) {
            const userRoles = yield actions.receiveUserRoles( '/matt-watson/secure-blocks/v1/user-roles/' );
            return actions.setUserRoles( userRoles );
        },
    },
} );

I've updated my tutorial: https://mwatson.co.uk/working-with-gutenberg-and-the-wordpress-rest-api/

I've cracked it!

const actions = {
    setUserRoles( userRoles ) {
        return {
            type: 'SET_USER_ROLES',
            userRoles,
        };
    },

    receiveUserRoles( path ) {
        return {
            type: 'RECEIVE_USER_ROLES',
            path,
        };
    },
};

const store = registerStore( 'matt-watson/secure-block', {
    reducer( state = { userRoles: {} }, action ) {

        switch ( action.type ) {
            case 'SET_USER_ROLES':
                return {
                    ...state,
                    userRoles: action.userRoles,
                };
            case 'RECEIVE_USER_ROLES':
                return action.userRoles;
        }

        return state;
    },

    actions,

    selectors: {
        receiveUserRoles( state ) {
            const { userRoles } = state;
            return userRoles;
        },
    },

    resolvers: {
        * receiveUserRoles( state ) {
            const userRoles = apiFetch( { path: '/matt-watson/secure-blocks/v1/user-roles/' } )
                .then( userRoles => {
                    return actions.setUserRoles( userRoles );
                } )
            yield userRoles;
        },
    },

} );

This sets the state of the userRoles and returns the userRoles once resolved.

You can then access this like so:

....

edit: withSelect( ( select ) => {
                return {
                    roles: select('matt-watson/secure-block').receiveUserRoles(),
                };
            } )( props => {

....