/**
 * @template T
 * @typedef {[T, T]} TPair
 */
/** @type {TPair<number>} */
var tp = [1,2]

TPair doesn't correctly create a generic type alias.

Expected behavior:

TPair's typedef is equivalent to type TPair<T> = [T, T]

Actual behavior:

TPair's typedef is equivalent to type T; type TPair = [T, T] (where T is unique and inexpressible). So @type {TPair} is legal, but nothing can be assigned to it, and @type {TPair<number>} says that TPair is not generic.