What is a goroutine leak and what is the idiomatic way to prevent one?

// LEAK — goroutine blocks forever; nobody ever sends to ch
func leaky() {
    ch := make(chan int)
    go func() {
        v := <-ch         // blocks indefinitely
        fmt.Println(v)
    }()
    // function returns — goroutine is stuck forever!
}

// FIX: pass a context and select on ctx.Done()
func safe(ctx context.Context, ch <-chan int) {
    go func() {
        select {
        case v := <-ch:
            fmt.Println(v)
        case <-ctx.Done():  // goroutine exits cleanly when cancelled
            return
        }
    }()
}

// FIX: close the channel to unblock receivers
func producer() <-chan int {
    ch := make(chan int)
    go func() {
        defer close(ch)   // close signals: no more values
        for _, v := range data {
            ch <- v
        }
    }()
    return ch
}

// Detect leaks in tests:
// defer goleak.VerifyNone(t)  — fails test if goroutines remain
// runtime.NumGoroutine()      — watch for steady growth