This trick fits more into the "prank" category.

    package main
    
    import "fmt"
    
    // <Add one short line of valid Go code here>
    
    func main() {
    	var n int = 1
    	fmt.Println(n)
    }
    
    Compiler: "prog.go:8: cannot use 1 (type int) as type int in assignment"

Here's a trick that I expected to work but doesn't. Would be interested to hear the rationale if anyone knows it.

    m := map[[]int]int{}