Go: all goroutines are asleep — deadlock! with an unbuffered channel

func main() {
    ch := make(chan int)
    ch <- 1
    fmt.Println(<-ch)
}

Why does this deadlock?

A send on an unbuffered channel blocks until another goroutine receives. main is the only goroutine, so it blocks on the send forever. Either receive in another goroutine, or give the channel a buffer:

ch := make(chan int, 1)
ch <- 1
fmt.Println(<-ch)