<?php

/**
 * @template TSend
 * @template TReturn of Traversable
 *
 * @param TSend $send
 * @param TReturn $return
 * @return TReturn<TSend>
 */
function doSomething($send, $return) {

}

Currently, Hover will look like this
function doSomething(TSend $send, TReturn $return): TReturn
They might confuse us that TSend and TReturn are real data type. We should make them clearer, for example:
function function doSomething<TSend, TReturn of Traversable>(TSend $send, TReturn $return): TReturn

    a month later

    Implemented;

    Since the next update, tooltips will include the generic type arguments, i.e.:

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