rust/tests/ui/generics/generic-non-trailing-defaults.rs

struct Heap;

struct Vec<A = Heap, T>(A, T);
//~^ ERROR generic parameters with a default must be trailing

struct Foo<A, B = Vec<C>, C>(A, B, C);
//~^ ERROR generic parameters with a default must be trailing
//~| ERROR generic parameter defaults cannot reference parameters before they are declared

fn main() {}