fieldless FRU can be used on non-struct-like structs

[arielb1]

STR

struct Foo(u32);

fn main() {
    let x = Foo(42);
    let _ = Foo { ..x };
}

Result

This compiles and runs.

Expected

This shouldn't compile.

[alexcrichton]

Nominating

[arielb1]

This issue also occurs in patterns, but there's also the additional issue of Ty-aliases being too transparent (instantiate_path):

struct Foo<T> { x: T }
type Ty = Foo<u32>;
fn main() {
    match (Foo { x: () }) { Ty::<()> { x } => {} }
}