src/test/run-pass/dst-field-align.rs

// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

struct Foo<T: ?Sized> {
    a: u16,
    b: T
}

trait Bar {
    fn get(&self) -> usize;
}

impl Bar for usize {
    fn get(&self) -> usize { *self }
}

struct Baz<T: ?Sized> {
    a: T
}

#[repr(packed)]
struct Packed<T: ?Sized> {
    a: u8,
    b: T
}

struct HasDrop<T: ?Sized> {
    ptr: Box<usize>,
    data: T
}

fn main() {
    // Test that zero-offset works properly
    let b : Baz<usize> = Baz { a: 7 };
    assert_eq!(b.a.get(), 7);
    let b : &Baz<Bar> = &b;
    assert_eq!(b.a.get(), 7);

    // Test that the field is aligned properly
    let f : Foo<usize> = Foo { a: 0, b: 11 };
    assert_eq!(f.b.get(), 11);
    let ptr1 : *const u8 = &f.b as *const _ as *const u8;

    let f : &Foo<Bar> = &f;
    let ptr2 : *const u8 = &f.b as *const _ as *const u8;
    assert_eq!(f.b.get(), 11);

    // The pointers should be the same
    assert_eq!(ptr1, ptr2);

    // Test that packed structs are handled correctly
    let p : Packed<usize> = Packed { a: 0, b: 13 };
    assert_eq!(p.b.get(), 13);
    let p : &Packed<Bar> = &p;
    assert_eq!(p.b.get(), 13);

    // Test that nested DSTs work properly
    let f : Foo<Foo<usize>> = Foo { a: 0, b: Foo { a: 1, b: 17 }};
    assert_eq!(f.b.b.get(), 17);
    let f : &Foo<Foo<Bar>> = &f;
    assert_eq!(f.b.b.get(), 17);

    // Test that get the pointer via destructuring works

    let f : Foo<usize> = Foo { a: 0, b: 11 };
    let f : &Foo<Bar> = &f;
    let &Foo { a: _, b: ref bar } = f;
    assert_eq!(bar.get(), 11);

    // Make sure that drop flags don't screw things up

    let d : HasDrop<Baz<[i32; 4]>> = HasDrop {
        ptr: Box::new(0),
        data: Baz { a: [1,2,3,4] }
    };
    assert_eq!([1,2,3,4], d.data.a);

    let d : &HasDrop<Baz<[i32]>> = &d;
    assert_eq!(&[1,2,3,4], &d.data.a);
}