rust/src/test/ui/specialization/non-defaulted-item-fail.rs

#![feature(specialization, associated_type_defaults)]

// Test that attempting to override a non-default method or one not in the
// parent impl causes an error.

trait Foo {
    type Ty = ();
    const CONST: u8 = 123;
    fn foo(&self) -> bool { true }
}

// Specialization tree for Foo:
//
//       Box<T>              Vec<T>
//        / \                 / \
// Box<i32>  Box<i64>   Vec<()>  Vec<bool>

impl<T> Foo for Box<T> {
    type Ty = bool;
    const CONST: u8 = 0;
    fn foo(&self) -> bool { false }
}

// Allowed
impl Foo for Box<i32> {}

// Can't override a non-`default` fn
impl Foo for Box<i64> {
    type Ty = Vec<()>;
//~^ error: `Ty` specializes an item from a parent `impl`, but that item is not marked `default`
    const CONST: u8 = 42;
//~^ error: `CONST` specializes an item from a parent `impl`, but that item is not marked `default`
    fn foo(&self) -> bool { true }
//~^ error: `foo` specializes an item from a parent `impl`, but that item is not marked `default`
}


// Doesn't mention the item = provided body/value is used and the method is final.
impl<T> Foo for Vec<T> {}

// Allowed
impl Foo for Vec<()> {}

impl Foo for Vec<bool> {
    type Ty = Vec<()>;
//~^ error: `Ty` specializes an item from a parent `impl`, but that item is not marked `default`
    const CONST: u8 = 42;
//~^ error: `CONST` specializes an item from a parent `impl`, but that item is not marked `default`
    fn foo(&self) -> bool { true }
//~^ error: `foo` specializes an item from a parent `impl`, but that item is not marked `default`
}

fn main() {}