use std::borrow::Cow;
use std::collections::TryReserveError::*;
use std::mem::size_of;
use std::panic::{catch_unwind, AssertUnwindSafe};
use std::vec::{Drain, IntoIter};

struct DropCounter<'a> {
    count: &'a mut u32,
}

impl Drop for DropCounter<'_> {
    fn drop(&mut self) {
        *self.count += 1;
    }
}

#[test]
fn test_small_vec_struct() {
    assert!(size_of::<Vec<u8>>() == size_of::<usize>() * 3);
}

#[test]
fn test_double_drop() {
    struct TwoVec<T> {
        x: Vec<T>,
        y: Vec<T>,
    }

    let (mut count_x, mut count_y) = (0, 0);
    {
        let mut tv = TwoVec { x: Vec::new(), y: Vec::new() };
        tv.x.push(DropCounter { count: &mut count_x });
        tv.y.push(DropCounter { count: &mut count_y });

        // If Vec had a drop flag, here is where it would be zeroed.
        // Instead, it should rely on its internal state to prevent
        // doing anything significant when dropped multiple times.
        drop(tv.x);

        // Here tv goes out of scope, tv.y should be dropped, but not tv.x.
    }

    assert_eq!(count_x, 1);
    assert_eq!(count_y, 1);
}

#[test]
fn test_reserve() {
    let mut v = Vec::new();
    assert_eq!(v.capacity(), 0);

    v.reserve(2);
    assert!(v.capacity() >= 2);

    for i in 0..16 {
        v.push(i);
    }

    assert!(v.capacity() >= 16);
    v.reserve(16);
    assert!(v.capacity() >= 32);

    v.push(16);

    v.reserve(16);
    assert!(v.capacity() >= 33)
}

#[test]
fn test_zst_capacity() {
    assert_eq!(Vec::<()>::new().capacity(), usize::max_value());
}

#[test]
fn test_extend() {
    let mut v = Vec::new();
    let mut w = Vec::new();

    v.extend(w.clone());
    assert_eq!(v, &[]);

    v.extend(0..3);
    for i in 0..3 {
        w.push(i)
    }

    assert_eq!(v, w);

    v.extend(3..10);
    for i in 3..10 {
        w.push(i)
    }

    assert_eq!(v, w);

    v.extend(w.clone()); // specializes to `append`
    assert!(v.iter().eq(w.iter().chain(w.iter())));

    // Zero sized types
    #[derive(PartialEq, Debug)]
    struct Foo;

    let mut a = Vec::new();
    let b = vec![Foo, Foo];

    a.extend(b);
    assert_eq!(a, &[Foo, Foo]);

    // Double drop
    let mut count_x = 0;
    {
        let mut x = Vec::new();
        let y = vec![DropCounter { count: &mut count_x }];
        x.extend(y);
    }
    assert_eq!(count_x, 1);
}

#[test]
fn test_extend_ref() {
    let mut v = vec![1, 2];
    v.extend(&[3, 4, 5]);

    assert_eq!(v.len(), 5);
    assert_eq!(v, [1, 2, 3, 4, 5]);

    let w = vec![6, 7];
    v.extend(&w);

    assert_eq!(v.len(), 7);
    assert_eq!(v, [1, 2, 3, 4, 5, 6, 7]);
}

#[test]
fn test_remove_item() {
    let mut v = vec![1, 2, 3];
    v.remove_item(&1);

    assert_eq!(v.len(), 2);
    assert_eq!(v, [2, 3]);

    let mut w = vec![1, 2, 3];
    w.remove_item(&4);

    assert_eq!(w.len(), 3);
    w.remove_item(&4);
}

#[test]
fn test_slice_from_mut() {
    let mut values = vec![1, 2, 3, 4, 5];
    {
        let slice = &mut values[2..];
        assert!(slice == [3, 4, 5]);
        for p in slice {
            *p += 2;
        }
    }

    assert!(values == [1, 2, 5, 6, 7]);
}

#[test]
fn test_slice_to_mut() {
    let mut values = vec![1, 2, 3, 4, 5];
    {
        let slice = &mut values[..2];
        assert!(slice == [1, 2]);
        for p in slice {
            *p += 1;
        }
    }

    assert!(values == [2, 3, 3, 4, 5]);
}

#[test]
fn test_split_at_mut() {
    let mut values = vec![1, 2, 3, 4, 5];
    {
        let (left, right) = values.split_at_mut(2);
        {
            let left: &[_] = left;
            assert!(&left[..left.len()] == &[1, 2]);
        }
        for p in left {
            *p += 1;
        }

        {
            let right: &[_] = right;
            assert!(&right[..right.len()] == &[3, 4, 5]);
        }
        for p in right {
            *p += 2;
        }
    }

    assert_eq!(values, [2, 3, 5, 6, 7]);
}

#[test]
fn test_clone() {
    let v: Vec<i32> = vec![];
    let w = vec![1, 2, 3];

    assert_eq!(v, v.clone());

    let z = w.clone();
    assert_eq!(w, z);
    // they should be disjoint in memory.
    assert!(w.as_ptr() != z.as_ptr())
}

#[test]
fn test_clone_from() {
    let mut v = vec![];
    let three: Vec<Box<_>> = vec![box 1, box 2, box 3];
    let two: Vec<Box<_>> = vec![box 4, box 5];
    // zero, long
    v.clone_from(&three);
    assert_eq!(v, three);

    // equal
    v.clone_from(&three);
    assert_eq!(v, three);

    // long, short
    v.clone_from(&two);
    assert_eq!(v, two);

    // short, long
    v.clone_from(&three);
    assert_eq!(v, three)
}

#[test]
fn test_retain() {
    let mut vec = vec![1, 2, 3, 4];
    vec.retain(|&x| x % 2 == 0);
    assert_eq!(vec, [2, 4]);
}

#[test]
fn test_dedup() {
    fn case(a: Vec<i32>, b: Vec<i32>) {
        let mut v = a;
        v.dedup();
        assert_eq!(v, b);
    }
    case(vec![], vec![]);
    case(vec![1], vec![1]);
    case(vec![1, 1], vec![1]);
    case(vec![1, 2, 3], vec![1, 2, 3]);
    case(vec![1, 1, 2, 3], vec![1, 2, 3]);
    case(vec![1, 2, 2, 3], vec![1, 2, 3]);
    case(vec![1, 2, 3, 3], vec![1, 2, 3]);
    case(vec![1, 1, 2, 2, 2, 3, 3], vec![1, 2, 3]);
}

#[test]
fn test_dedup_by_key() {
    fn case(a: Vec<i32>, b: Vec<i32>) {
        let mut v = a;
        v.dedup_by_key(|i| *i / 10);
        assert_eq!(v, b);
    }
    case(vec![], vec![]);
    case(vec![10], vec![10]);
    case(vec![10, 11], vec![10]);
    case(vec![10, 20, 30], vec![10, 20, 30]);
    case(vec![10, 11, 20, 30], vec![10, 20, 30]);
    case(vec![10, 20, 21, 30], vec![10, 20, 30]);
    case(vec![10, 20, 30, 31], vec![10, 20, 30]);
    case(vec![10, 11, 20, 21, 22, 30, 31], vec![10, 20, 30]);
}

#[test]
fn test_dedup_by() {
    let mut vec = vec!["foo", "bar", "Bar", "baz", "bar"];
    vec.dedup_by(|a, b| a.eq_ignore_ascii_case(b));

    assert_eq!(vec, ["foo", "bar", "baz", "bar"]);

    let mut vec = vec![("foo", 1), ("foo", 2), ("bar", 3), ("bar", 4), ("bar", 5)];
    vec.dedup_by(|a, b| {
        a.0 == b.0 && {
            b.1 += a.1;
            true
        }
    });

    assert_eq!(vec, [("foo", 3), ("bar", 12)]);
}

#[test]
fn test_dedup_unique() {
    let mut v0: Vec<Box<_>> = vec![box 1, box 1, box 2, box 3];
    v0.dedup();
    let mut v1: Vec<Box<_>> = vec![box 1, box 2, box 2, box 3];
    v1.dedup();
    let mut v2: Vec<Box<_>> = vec![box 1, box 2, box 3, box 3];
    v2.dedup();
    // If the boxed pointers were leaked or otherwise misused, valgrind
    // and/or rt should raise errors.
}

#[test]
fn zero_sized_values() {
    let mut v = Vec::new();
    assert_eq!(v.len(), 0);
    v.push(());
    assert_eq!(v.len(), 1);
    v.push(());
    assert_eq!(v.len(), 2);
    assert_eq!(v.pop(), Some(()));
    assert_eq!(v.pop(), Some(()));
    assert_eq!(v.pop(), None);

    assert_eq!(v.iter().count(), 0);
    v.push(());
    assert_eq!(v.iter().count(), 1);
    v.push(());
    assert_eq!(v.iter().count(), 2);

    for &() in &v {}

    assert_eq!(v.iter_mut().count(), 2);
    v.push(());
    assert_eq!(v.iter_mut().count(), 3);
    v.push(());
    assert_eq!(v.iter_mut().count(), 4);

    for &mut () in &mut v {}
    unsafe {
        v.set_len(0);
    }
    assert_eq!(v.iter_mut().count(), 0);
}

#[test]
fn test_partition() {
    assert_eq!(vec![].into_iter().partition(|x: &i32| *x < 3), (vec![], vec![]));
    assert_eq!(vec![1, 2, 3].into_iter().partition(|x| *x < 4), (vec![1, 2, 3], vec![]));
    assert_eq!(vec![1, 2, 3].into_iter().partition(|x| *x < 2), (vec![1], vec![2, 3]));
    assert_eq!(vec![1, 2, 3].into_iter().partition(|x| *x < 0), (vec![], vec![1, 2, 3]));
}

#[test]
fn test_zip_unzip() {
    let z1 = vec![(1, 4), (2, 5), (3, 6)];

    let (left, right): (Vec<_>, Vec<_>) = z1.iter().cloned().unzip();

    assert_eq!((1, 4), (left[0], right[0]));
    assert_eq!((2, 5), (left[1], right[1]));
    assert_eq!((3, 6), (left[2], right[2]));
}

#[test]
fn test_vec_truncate_drop() {
    static mut DROPS: u32 = 0;
    struct Elem(i32);
    impl Drop for Elem {
        fn drop(&mut self) {
            unsafe {
                DROPS += 1;
            }
        }
    }

    let mut v = vec![Elem(1), Elem(2), Elem(3), Elem(4), Elem(5)];
    assert_eq!(unsafe { DROPS }, 0);
    v.truncate(3);
    assert_eq!(unsafe { DROPS }, 2);
    v.truncate(0);
    assert_eq!(unsafe { DROPS }, 5);
}

#[test]
#[should_panic]
fn test_vec_truncate_fail() {
    struct BadElem(i32);
    impl Drop for BadElem {
        fn drop(&mut self) {
            let BadElem(ref mut x) = *self;
            if *x == 0xbadbeef {
                panic!("BadElem panic: 0xbadbeef")
            }
        }
    }

    let mut v = vec![BadElem(1), BadElem(2), BadElem(0xbadbeef), BadElem(4)];
    v.truncate(0);
}

#[test]
fn test_index() {
    let vec = vec![1, 2, 3];
    assert!(vec[1] == 2);
}

#[test]
#[should_panic]
fn test_index_out_of_bounds() {
    let vec = vec![1, 2, 3];
    let _ = vec[3];
}

#[test]
#[should_panic]
fn test_slice_out_of_bounds_1() {
    let x = vec![1, 2, 3, 4, 5];
    &x[!0..];
}

#[test]
#[should_panic]
fn test_slice_out_of_bounds_2() {
    let x = vec![1, 2, 3, 4, 5];
    &x[..6];
}

#[test]
#[should_panic]
fn test_slice_out_of_bounds_3() {
    let x = vec![1, 2, 3, 4, 5];
    &x[!0..4];
}

#[test]
#[should_panic]
fn test_slice_out_of_bounds_4() {
    let x = vec![1, 2, 3, 4, 5];
    &x[1..6];
}

#[test]
#[should_panic]
fn test_slice_out_of_bounds_5() {
    let x = vec![1, 2, 3, 4, 5];
    &x[3..2];
}

#[test]
#[should_panic]
fn test_swap_remove_empty() {
    let mut vec = Vec::<i32>::new();
    vec.swap_remove(0);
}

#[test]
fn test_move_items() {
    let vec = vec![1, 2, 3];
    let mut vec2 = vec![];
    for i in vec {
        vec2.push(i);
    }
    assert_eq!(vec2, [1, 2, 3]);
}

#[test]
fn test_move_items_reverse() {
    let vec = vec![1, 2, 3];
    let mut vec2 = vec![];
    for i in vec.into_iter().rev() {
        vec2.push(i);
    }
    assert_eq!(vec2, [3, 2, 1]);
}

#[test]
fn test_move_items_zero_sized() {
    let vec = vec![(), (), ()];
    let mut vec2 = vec![];
    for i in vec {
        vec2.push(i);
    }
    assert_eq!(vec2, [(), (), ()]);
}

#[test]
fn test_drain_items() {
    let mut vec = vec![1, 2, 3];
    let mut vec2 = vec![];
    for i in vec.drain(..) {
        vec2.push(i);
    }
    assert_eq!(vec, []);
    assert_eq!(vec2, [1, 2, 3]);
}

#[test]
fn test_drain_items_reverse() {
    let mut vec = vec![1, 2, 3];
    let mut vec2 = vec![];
    for i in vec.drain(..).rev() {
        vec2.push(i);
    }
    assert_eq!(vec, []);
    assert_eq!(vec2, [3, 2, 1]);
}

#[test]
fn test_drain_items_zero_sized() {
    let mut vec = vec![(), (), ()];
    let mut vec2 = vec![];
    for i in vec.drain(..) {
        vec2.push(i);
    }
    assert_eq!(vec, []);
    assert_eq!(vec2, [(), (), ()]);
}

#[test]
#[should_panic]
fn test_drain_out_of_bounds() {
    let mut v = vec![1, 2, 3, 4, 5];
    v.drain(5..6);
}

#[test]
fn test_drain_range() {
    let mut v = vec![1, 2, 3, 4, 5];
    for _ in v.drain(4..) {}
    assert_eq!(v, &[1, 2, 3, 4]);

    let mut v: Vec<_> = (1..6).map(|x| x.to_string()).collect();
    for _ in v.drain(1..4) {}
    assert_eq!(v, &[1.to_string(), 5.to_string()]);

    let mut v: Vec<_> = (1..6).map(|x| x.to_string()).collect();
    for _ in v.drain(1..4).rev() {}
    assert_eq!(v, &[1.to_string(), 5.to_string()]);

    let mut v: Vec<_> = vec![(); 5];
    for _ in v.drain(1..4).rev() {}
    assert_eq!(v, &[(), ()]);
}

#[test]
fn test_drain_inclusive_range() {
    let mut v = vec!['a', 'b', 'c', 'd', 'e'];
    for _ in v.drain(1..=3) {}
    assert_eq!(v, &['a', 'e']);

    let mut v: Vec<_> = (0..=5).map(|x| x.to_string()).collect();
    for _ in v.drain(1..=5) {}
    assert_eq!(v, &["0".to_string()]);

    let mut v: Vec<String> = (0..=5).map(|x| x.to_string()).collect();
    for _ in v.drain(0..=5) {}
    assert_eq!(v, Vec::<String>::new());

    let mut v: Vec<_> = (0..=5).map(|x| x.to_string()).collect();
    for _ in v.drain(0..=3) {}
    assert_eq!(v, &["4".to_string(), "5".to_string()]);

    let mut v: Vec<_> = (0..=1).map(|x| x.to_string()).collect();
    for _ in v.drain(..=0) {}
    assert_eq!(v, &["1".to_string()]);
}

#[test]
fn test_drain_max_vec_size() {
    let mut v = Vec::<()>::with_capacity(usize::max_value());
    unsafe {
        v.set_len(usize::max_value());
    }
    for _ in v.drain(usize::max_value() - 1..) {}
    assert_eq!(v.len(), usize::max_value() - 1);

    let mut v = Vec::<()>::with_capacity(usize::max_value());
    unsafe {
        v.set_len(usize::max_value());
    }
    for _ in v.drain(usize::max_value() - 1..=usize::max_value() - 1) {}
    assert_eq!(v.len(), usize::max_value() - 1);
}

#[test]
#[should_panic]
fn test_drain_inclusive_out_of_bounds() {
    let mut v = vec![1, 2, 3, 4, 5];
    v.drain(5..=5);
}

#[test]
fn test_drain_leak() {
    static mut DROPS: i32 = 0;

    #[derive(Debug, PartialEq)]
    struct D(u32, bool);

    impl Drop for D {
        fn drop(&mut self) {
            unsafe {
                DROPS += 1;
            }

            if self.1 {
                panic!("panic in `drop`");
            }
        }
    }

    let mut v = vec![
        D(0, false),
        D(1, false),
        D(2, false),
        D(3, false),
        D(4, true),
        D(5, false),
        D(6, false),
    ];

    catch_unwind(AssertUnwindSafe(|| {
        v.drain(2..=5);
    }))
    .ok();

    assert_eq!(unsafe { DROPS }, 4);
    assert_eq!(v, vec![D(0, false), D(1, false), D(6, false),]);
}

#[test]
fn test_splice() {
    let mut v = vec![1, 2, 3, 4, 5];
    let a = [10, 11, 12];
    v.splice(2..4, a.iter().cloned());
    assert_eq!(v, &[1, 2, 10, 11, 12, 5]);
    v.splice(1..3, Some(20));
    assert_eq!(v, &[1, 20, 11, 12, 5]);
}

#[test]
fn test_splice_inclusive_range() {
    let mut v = vec![1, 2, 3, 4, 5];
    let a = [10, 11, 12];
    let t1: Vec<_> = v.splice(2..=3, a.iter().cloned()).collect();
    assert_eq!(v, &[1, 2, 10, 11, 12, 5]);
    assert_eq!(t1, &[3, 4]);
    let t2: Vec<_> = v.splice(1..=2, Some(20)).collect();
    assert_eq!(v, &[1, 20, 11, 12, 5]);
    assert_eq!(t2, &[2, 10]);
}

#[test]
#[should_panic]
fn test_splice_out_of_bounds() {
    let mut v = vec![1, 2, 3, 4, 5];
    let a = [10, 11, 12];
    v.splice(5..6, a.iter().cloned());
}

#[test]
#[should_panic]
fn test_splice_inclusive_out_of_bounds() {
    let mut v = vec![1, 2, 3, 4, 5];
    let a = [10, 11, 12];
    v.splice(5..=5, a.iter().cloned());
}

#[test]
fn test_splice_items_zero_sized() {
    let mut vec = vec![(), (), ()];
    let vec2 = vec![];
    let t: Vec<_> = vec.splice(1..2, vec2.iter().cloned()).collect();
    assert_eq!(vec, &[(), ()]);
    assert_eq!(t, &[()]);
}

#[test]
fn test_splice_unbounded() {
    let mut vec = vec![1, 2, 3, 4, 5];
    let t: Vec<_> = vec.splice(.., None).collect();
    assert_eq!(vec, &[]);
    assert_eq!(t, &[1, 2, 3, 4, 5]);
}

#[test]
fn test_splice_forget() {
    let mut v = vec![1, 2, 3, 4, 5];
    let a = [10, 11, 12];
    std::mem::forget(v.splice(2..4, a.iter().cloned()));
    assert_eq!(v, &[1, 2]);
}

#[test]
fn test_into_boxed_slice() {
    let xs = vec![1, 2, 3];
    let ys = xs.into_boxed_slice();
    assert_eq!(&*ys, [1, 2, 3]);
}

#[test]
fn test_append() {
    let mut vec = vec![1, 2, 3];
    let mut vec2 = vec![4, 5, 6];
    vec.append(&mut vec2);
    assert_eq!(vec, [1, 2, 3, 4, 5, 6]);
    assert_eq!(vec2, []);
}

#[test]
fn test_split_off() {
    let mut vec = vec![1, 2, 3, 4, 5, 6];
    let vec2 = vec.split_off(4);
    assert_eq!(vec, [1, 2, 3, 4]);
    assert_eq!(vec2, [5, 6]);
}

#[test]
fn test_into_iter_as_slice() {
    let vec = vec!['a', 'b', 'c'];
    let mut into_iter = vec.into_iter();
    assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
    let _ = into_iter.next().unwrap();
    assert_eq!(into_iter.as_slice(), &['b', 'c']);
    let _ = into_iter.next().unwrap();
    let _ = into_iter.next().unwrap();
    assert_eq!(into_iter.as_slice(), &[]);
}

#[test]
fn test_into_iter_as_mut_slice() {
    let vec = vec!['a', 'b', 'c'];
    let mut into_iter = vec.into_iter();
    assert_eq!(into_iter.as_slice(), &['a', 'b', 'c']);
    into_iter.as_mut_slice()[0] = 'x';
    into_iter.as_mut_slice()[1] = 'y';
    assert_eq!(into_iter.next().unwrap(), 'x');
    assert_eq!(into_iter.as_slice(), &['y', 'c']);
}

#[test]
fn test_into_iter_debug() {
    let vec = vec!['a', 'b', 'c'];
    let into_iter = vec.into_iter();
    let debug = format!("{:?}", into_iter);
    assert_eq!(debug, "IntoIter(['a', 'b', 'c'])");
}

#[test]
fn test_into_iter_count() {
    assert_eq!(vec![1, 2, 3].into_iter().count(), 3);
}

#[test]
fn test_into_iter_clone() {
    fn iter_equal<I: Iterator<Item = i32>>(it: I, slice: &[i32]) {
        let v: Vec<i32> = it.collect();
        assert_eq!(&v[..], slice);
    }
    let mut it = vec![1, 2, 3].into_iter();
    iter_equal(it.clone(), &[1, 2, 3]);
    assert_eq!(it.next(), Some(1));
    let mut it = it.rev();
    iter_equal(it.clone(), &[3, 2]);
    assert_eq!(it.next(), Some(3));
    iter_equal(it.clone(), &[2]);
    assert_eq!(it.next(), Some(2));
    iter_equal(it.clone(), &[]);
    assert_eq!(it.next(), None);
}

#[test]
fn test_into_iter_leak() {
    static mut DROPS: i32 = 0;

    struct D(bool);

    impl Drop for D {
        fn drop(&mut self) {
            unsafe {
                DROPS += 1;
            }

            if self.0 {
                panic!("panic in `drop`");
            }
        }
    }

    let v = vec![D(false), D(true), D(false)];

    catch_unwind(move || drop(v.into_iter())).ok();

    assert_eq!(unsafe { DROPS }, 3);
}

#[test]
fn test_cow_from() {
    let borrowed: &[_] = &["borrowed", "(slice)"];
    let owned = vec!["owned", "(vec)"];
    match (Cow::from(owned.clone()), Cow::from(borrowed)) {
        (Cow::Owned(o), Cow::Borrowed(b)) => assert!(o == owned && b == borrowed),
        _ => panic!("invalid `Cow::from`"),
    }
}

#[test]
fn test_from_cow() {
    let borrowed: &[_] = &["borrowed", "(slice)"];
    let owned = vec!["owned", "(vec)"];
    assert_eq!(Vec::from(Cow::Borrowed(borrowed)), vec!["borrowed", "(slice)"]);
    assert_eq!(Vec::from(Cow::Owned(owned)), vec!["owned", "(vec)"]);
}

#[allow(dead_code)]
fn assert_covariance() {
    fn drain<'new>(d: Drain<'static, &'static str>) -> Drain<'new, &'new str> {
        d
    }
    fn into_iter<'new>(i: IntoIter<&'static str>) -> IntoIter<&'new str> {
        i
    }
}

#[test]
fn from_into_inner() {
    let vec = vec![1, 2, 3];
    let ptr = vec.as_ptr();
    let vec = vec.into_iter().collect::<Vec<_>>();
    assert_eq!(vec, [1, 2, 3]);
    assert_eq!(vec.as_ptr(), ptr);

    let ptr = &vec[1] as *const _;
    let mut it = vec.into_iter();
    it.next().unwrap();
    let vec = it.collect::<Vec<_>>();
    assert_eq!(vec, [2, 3]);
    assert!(ptr != vec.as_ptr());
}

#[test]
fn overaligned_allocations() {
    #[repr(align(256))]
    struct Foo(usize);
    let mut v = vec![Foo(273)];
    for i in 0..0x1000 {
        v.reserve_exact(i);
        assert!(v[0].0 == 273);
        assert!(v.as_ptr() as usize & 0xff == 0);
        v.shrink_to_fit();
        assert!(v[0].0 == 273);
        assert!(v.as_ptr() as usize & 0xff == 0);
    }
}

#[test]
fn drain_filter_empty() {
    let mut vec: Vec<i32> = vec![];

    {
        let mut iter = vec.drain_filter(|_| true);
        assert_eq!(iter.size_hint(), (0, Some(0)));
        assert_eq!(iter.next(), None);
        assert_eq!(iter.size_hint(), (0, Some(0)));
        assert_eq!(iter.next(), None);
        assert_eq!(iter.size_hint(), (0, Some(0)));
    }
    assert_eq!(vec.len(), 0);
    assert_eq!(vec, vec![]);
}

#[test]
fn drain_filter_zst() {
    let mut vec = vec![(), (), (), (), ()];
    let initial_len = vec.len();
    let mut count = 0;
    {
        let mut iter = vec.drain_filter(|_| true);
        assert_eq!(iter.size_hint(), (0, Some(initial_len)));
        while let Some(_) = iter.next() {
            count += 1;
            assert_eq!(iter.size_hint(), (0, Some(initial_len - count)));
        }
        assert_eq!(iter.size_hint(), (0, Some(0)));
        assert_eq!(iter.next(), None);
        assert_eq!(iter.size_hint(), (0, Some(0)));
    }

    assert_eq!(count, initial_len);
    assert_eq!(vec.len(), 0);
    assert_eq!(vec, vec![]);
}

#[test]
fn drain_filter_false() {
    let mut vec = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

    let initial_len = vec.len();
    let mut count = 0;
    {
        let mut iter = vec.drain_filter(|_| false);
        assert_eq!(iter.size_hint(), (0, Some(initial_len)));
        for _ in iter.by_ref() {
            count += 1;
        }
        assert_eq!(iter.size_hint(), (0, Some(0)));
        assert_eq!(iter.next(), None);
        assert_eq!(iter.size_hint(), (0, Some(0)));
    }

    assert_eq!(count, 0);
    assert_eq!(vec.len(), initial_len);
    assert_eq!(vec, vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10]);
}

#[test]
fn drain_filter_true() {
    let mut vec = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

    let initial_len = vec.len();
    let mut count = 0;
    {
        let mut iter = vec.drain_filter(|_| true);
        assert_eq!(iter.size_hint(), (0, Some(initial_len)));
        while let Some(_) = iter.next() {
            count += 1;
            assert_eq!(iter.size_hint(), (0, Some(initial_len - count)));
        }
        assert_eq!(iter.size_hint(), (0, Some(0)));
        assert_eq!(iter.next(), None);
        assert_eq!(iter.size_hint(), (0, Some(0)));
    }

    assert_eq!(count, initial_len);
    assert_eq!(vec.len(), 0);
    assert_eq!(vec, vec![]);
}

#[test]
fn drain_filter_complex() {
    {
        //                [+xxx++++++xxxxx++++x+x++]
        let mut vec = vec![
            1, 2, 4, 6, 7, 9, 11, 13, 15, 17, 18, 20, 22, 24, 26, 27, 29, 31, 33, 34, 35, 36, 37,
            39,
        ];

        let removed = vec.drain_filter(|x| *x % 2 == 0).collect::<Vec<_>>();
        assert_eq!(removed.len(), 10);
        assert_eq!(removed, vec![2, 4, 6, 18, 20, 22, 24, 26, 34, 36]);

        assert_eq!(vec.len(), 14);
        assert_eq!(vec, vec![1, 7, 9, 11, 13, 15, 17, 27, 29, 31, 33, 35, 37, 39]);
    }

    {
        //                [xxx++++++xxxxx++++x+x++]
        let mut vec = vec![
            2, 4, 6, 7, 9, 11, 13, 15, 17, 18, 20, 22, 24, 26, 27, 29, 31, 33, 34, 35, 36, 37, 39,
        ];

        let removed = vec.drain_filter(|x| *x % 2 == 0).collect::<Vec<_>>();
        assert_eq!(removed.len(), 10);
        assert_eq!(removed, vec![2, 4, 6, 18, 20, 22, 24, 26, 34, 36]);

        assert_eq!(vec.len(), 13);
        assert_eq!(vec, vec![7, 9, 11, 13, 15, 17, 27, 29, 31, 33, 35, 37, 39]);
    }

    {
        //                [xxx++++++xxxxx++++x+x]
        let mut vec =
            vec![2, 4, 6, 7, 9, 11, 13, 15, 17, 18, 20, 22, 24, 26, 27, 29, 31, 33, 34, 35, 36];

        let removed = vec.drain_filter(|x| *x % 2 == 0).collect::<Vec<_>>();
        assert_eq!(removed.len(), 10);
        assert_eq!(removed, vec![2, 4, 6, 18, 20, 22, 24, 26, 34, 36]);

        assert_eq!(vec.len(), 11);
        assert_eq!(vec, vec![7, 9, 11, 13, 15, 17, 27, 29, 31, 33, 35]);
    }

    {
        //                [xxxxxxxxxx+++++++++++]
        let mut vec = vec![2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19];

        let removed = vec.drain_filter(|x| *x % 2 == 0).collect::<Vec<_>>();
        assert_eq!(removed.len(), 10);
        assert_eq!(removed, vec![2, 4, 6, 8, 10, 12, 14, 16, 18, 20]);

        assert_eq!(vec.len(), 10);
        assert_eq!(vec, vec![1, 3, 5, 7, 9, 11, 13, 15, 17, 19]);
    }

    {
        //                [+++++++++++xxxxxxxxxx]
        let mut vec = vec![1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20];

        let removed = vec.drain_filter(|x| *x % 2 == 0).collect::<Vec<_>>();
        assert_eq!(removed.len(), 10);
        assert_eq!(removed, vec![2, 4, 6, 8, 10, 12, 14, 16, 18, 20]);

        assert_eq!(vec.len(), 10);
        assert_eq!(vec, vec![1, 3, 5, 7, 9, 11, 13, 15, 17, 19]);
    }
}

// FIXME: re-enable emscripten once it can unwind again
#[test]
#[cfg(not(target_os = "emscripten"))]
fn drain_filter_consumed_panic() {
    use std::rc::Rc;
    use std::sync::Mutex;

    struct Check {
        index: usize,
        drop_counts: Rc<Mutex<Vec<usize>>>,
    };

    impl Drop for Check {
        fn drop(&mut self) {
            self.drop_counts.lock().unwrap()[self.index] += 1;
            println!("drop: {}", self.index);
        }
    }

    let check_count = 10;
    let drop_counts = Rc::new(Mutex::new(vec![0_usize; check_count]));
    let mut data: Vec<Check> = (0..check_count)
        .map(|index| Check { index, drop_counts: Rc::clone(&drop_counts) })
        .collect();

    let _ = std::panic::catch_unwind(move || {
        let filter = |c: &mut Check| {
            if c.index == 2 {
                panic!("panic at index: {}", c.index);
            }
            // Verify that if the filter could panic again on another element
            // that it would not cause a double panic and all elements of the
            // vec would still be dropped exactly once.
            if c.index == 4 {
                panic!("panic at index: {}", c.index);
            }
            c.index < 6
        };
        let drain = data.drain_filter(filter);

        // NOTE: The DrainFilter is explicitly consumed
        drain.for_each(drop);
    });

    let drop_counts = drop_counts.lock().unwrap();
    assert_eq!(check_count, drop_counts.len());

    for (index, count) in drop_counts.iter().cloned().enumerate() {
        assert_eq!(1, count, "unexpected drop count at index: {} (count: {})", index, count);
    }
}

// FIXME: Re-enable emscripten once it can catch panics
#[test]
#[cfg(not(target_os = "emscripten"))]
fn drain_filter_unconsumed_panic() {
    use std::rc::Rc;
    use std::sync::Mutex;

    struct Check {
        index: usize,
        drop_counts: Rc<Mutex<Vec<usize>>>,
    };

    impl Drop for Check {
        fn drop(&mut self) {
            self.drop_counts.lock().unwrap()[self.index] += 1;
            println!("drop: {}", self.index);
        }
    }

    let check_count = 10;
    let drop_counts = Rc::new(Mutex::new(vec![0_usize; check_count]));
    let mut data: Vec<Check> = (0..check_count)
        .map(|index| Check { index, drop_counts: Rc::clone(&drop_counts) })
        .collect();

    let _ = std::panic::catch_unwind(move || {
        let filter = |c: &mut Check| {
            if c.index == 2 {
                panic!("panic at index: {}", c.index);
            }
            // Verify that if the filter could panic again on another element
            // that it would not cause a double panic and all elements of the
            // vec would still be dropped exactly once.
            if c.index == 4 {
                panic!("panic at index: {}", c.index);
            }
            c.index < 6
        };
        let _drain = data.drain_filter(filter);

        // NOTE: The DrainFilter is dropped without being consumed
    });

    let drop_counts = drop_counts.lock().unwrap();
    assert_eq!(check_count, drop_counts.len());

    for (index, count) in drop_counts.iter().cloned().enumerate() {
        assert_eq!(1, count, "unexpected drop count at index: {} (count: {})", index, count);
    }
}

#[test]
fn drain_filter_unconsumed() {
    let mut vec = vec![1, 2, 3, 4];
    let drain = vec.drain_filter(|&mut x| x % 2 != 0);
    drop(drain);
    assert_eq!(vec, [2, 4]);
}

#[test]
fn test_reserve_exact() {
    // This is all the same as test_reserve

    let mut v = Vec::new();
    assert_eq!(v.capacity(), 0);

    v.reserve_exact(2);
    assert!(v.capacity() >= 2);

    for i in 0..16 {
        v.push(i);
    }

    assert!(v.capacity() >= 16);
    v.reserve_exact(16);
    assert!(v.capacity() >= 32);

    v.push(16);

    v.reserve_exact(16);
    assert!(v.capacity() >= 33)
}

#[test]
#[cfg_attr(miri, ignore)] // Miri does not support signalling OOM
#[cfg_attr(target_os = "android", ignore)] // Android used in CI has a broken dlmalloc
fn test_try_reserve() {
    // These are the interesting cases:
    // * exactly isize::MAX should never trigger a CapacityOverflow (can be OOM)
    // * > isize::MAX should always fail
    //    * On 16/32-bit should CapacityOverflow
    //    * On 64-bit should OOM
    // * overflow may trigger when adding `len` to `cap` (in number of elements)
    // * overflow may trigger when multiplying `new_cap` by size_of::<T> (to get bytes)

    const MAX_CAP: usize = isize::MAX as usize;
    const MAX_USIZE: usize = usize::MAX;

    // On 16/32-bit, we check that allocations don't exceed isize::MAX,
    // on 64-bit, we assume the OS will give an OOM for such a ridiculous size.
    // Any platform that succeeds for these requests is technically broken with
    // ptr::offset because LLVM is the worst.
    let guards_against_isize = size_of::<usize>() < 8;

    {
        // Note: basic stuff is checked by test_reserve
        let mut empty_bytes: Vec<u8> = Vec::new();

        // Check isize::MAX doesn't count as an overflow
        if let Err(CapacityOverflow) = empty_bytes.try_reserve(MAX_CAP) {
            panic!("isize::MAX shouldn't trigger an overflow!");
        }
        // Play it again, frank! (just to be sure)
        if let Err(CapacityOverflow) = empty_bytes.try_reserve(MAX_CAP) {
            panic!("isize::MAX shouldn't trigger an overflow!");
        }

        if guards_against_isize {
            // Check isize::MAX + 1 does count as overflow
            if let Err(CapacityOverflow) = empty_bytes.try_reserve(MAX_CAP + 1) {
            } else {
                panic!("isize::MAX + 1 should trigger an overflow!")
            }

            // Check usize::MAX does count as overflow
            if let Err(CapacityOverflow) = empty_bytes.try_reserve(MAX_USIZE) {
            } else {
                panic!("usize::MAX should trigger an overflow!")
            }
        } else {
            // Check isize::MAX + 1 is an OOM
            if let Err(AllocError { .. }) = empty_bytes.try_reserve(MAX_CAP + 1) {
            } else {
                panic!("isize::MAX + 1 should trigger an OOM!")
            }

            // Check usize::MAX is an OOM
            if let Err(AllocError { .. }) = empty_bytes.try_reserve(MAX_USIZE) {
            } else {
                panic!("usize::MAX should trigger an OOM!")
            }
        }
    }

    {
        // Same basic idea, but with non-zero len
        let mut ten_bytes: Vec<u8> = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

        if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_CAP - 10) {
            panic!("isize::MAX shouldn't trigger an overflow!");
        }
        if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_CAP - 10) {
            panic!("isize::MAX shouldn't trigger an overflow!");
        }
        if guards_against_isize {
            if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_CAP - 9) {
            } else {
                panic!("isize::MAX + 1 should trigger an overflow!");
            }
        } else {
            if let Err(AllocError { .. }) = ten_bytes.try_reserve(MAX_CAP - 9) {
            } else {
                panic!("isize::MAX + 1 should trigger an OOM!")
            }
        }
        // Should always overflow in the add-to-len
        if let Err(CapacityOverflow) = ten_bytes.try_reserve(MAX_USIZE) {
        } else {
            panic!("usize::MAX should trigger an overflow!")
        }
    }

    {
        // Same basic idea, but with interesting type size
        let mut ten_u32s: Vec<u32> = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

        if let Err(CapacityOverflow) = ten_u32s.try_reserve(MAX_CAP / 4 - 10) {
            panic!("isize::MAX shouldn't trigger an overflow!");
        }
        if let Err(CapacityOverflow) = ten_u32s.try_reserve(MAX_CAP / 4 - 10) {
            panic!("isize::MAX shouldn't trigger an overflow!");
        }
        if guards_against_isize {
            if let Err(CapacityOverflow) = ten_u32s.try_reserve(MAX_CAP / 4 - 9) {
            } else {
                panic!("isize::MAX + 1 should trigger an overflow!");
            }
        } else {
            if let Err(AllocError { .. }) = ten_u32s.try_reserve(MAX_CAP / 4 - 9) {
            } else {
                panic!("isize::MAX + 1 should trigger an OOM!")
            }
        }
        // Should fail in the mul-by-size
        if let Err(CapacityOverflow) = ten_u32s.try_reserve(MAX_USIZE - 20) {
        } else {
            panic!("usize::MAX should trigger an overflow!");
        }
    }
}

#[test]
#[cfg_attr(miri, ignore)] // Miri does not support signalling OOM
#[cfg_attr(target_os = "android", ignore)] // Android used in CI has a broken dlmalloc
fn test_try_reserve_exact() {
    // This is exactly the same as test_try_reserve with the method changed.
    // See that test for comments.

    const MAX_CAP: usize = isize::MAX as usize;
    const MAX_USIZE: usize = usize::MAX;

    let guards_against_isize = size_of::<usize>() < 8;

    {
        let mut empty_bytes: Vec<u8> = Vec::new();

        if let Err(CapacityOverflow) = empty_bytes.try_reserve_exact(MAX_CAP) {
            panic!("isize::MAX shouldn't trigger an overflow!");
        }
        if let Err(CapacityOverflow) = empty_bytes.try_reserve_exact(MAX_CAP) {
            panic!("isize::MAX shouldn't trigger an overflow!");
        }

        if guards_against_isize {
            if let Err(CapacityOverflow) = empty_bytes.try_reserve_exact(MAX_CAP + 1) {
            } else {
                panic!("isize::MAX + 1 should trigger an overflow!")
            }

            if let Err(CapacityOverflow) = empty_bytes.try_reserve_exact(MAX_USIZE) {
            } else {
                panic!("usize::MAX should trigger an overflow!")
            }
        } else {
            if let Err(AllocError { .. }) = empty_bytes.try_reserve_exact(MAX_CAP + 1) {
            } else {
                panic!("isize::MAX + 1 should trigger an OOM!")
            }

            if let Err(AllocError { .. }) = empty_bytes.try_reserve_exact(MAX_USIZE) {
            } else {
                panic!("usize::MAX should trigger an OOM!")
            }
        }
    }

    {
        let mut ten_bytes: Vec<u8> = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

        if let Err(CapacityOverflow) = ten_bytes.try_reserve_exact(MAX_CAP - 10) {
            panic!("isize::MAX shouldn't trigger an overflow!");
        }
        if let Err(CapacityOverflow) = ten_bytes.try_reserve_exact(MAX_CAP - 10) {
            panic!("isize::MAX shouldn't trigger an overflow!");
        }
        if guards_against_isize {
            if let Err(CapacityOverflow) = ten_bytes.try_reserve_exact(MAX_CAP - 9) {
            } else {
                panic!("isize::MAX + 1 should trigger an overflow!");
            }
        } else {
            if let Err(AllocError { .. }) = ten_bytes.try_reserve_exact(MAX_CAP - 9) {
            } else {
                panic!("isize::MAX + 1 should trigger an OOM!")
            }
        }
        if let Err(CapacityOverflow) = ten_bytes.try_reserve_exact(MAX_USIZE) {
        } else {
            panic!("usize::MAX should trigger an overflow!")
        }
    }

    {
        let mut ten_u32s: Vec<u32> = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

        if let Err(CapacityOverflow) = ten_u32s.try_reserve_exact(MAX_CAP / 4 - 10) {
            panic!("isize::MAX shouldn't trigger an overflow!");
        }
        if let Err(CapacityOverflow) = ten_u32s.try_reserve_exact(MAX_CAP / 4 - 10) {
            panic!("isize::MAX shouldn't trigger an overflow!");
        }
        if guards_against_isize {
            if let Err(CapacityOverflow) = ten_u32s.try_reserve_exact(MAX_CAP / 4 - 9) {
            } else {
                panic!("isize::MAX + 1 should trigger an overflow!");
            }
        } else {
            if let Err(AllocError { .. }) = ten_u32s.try_reserve_exact(MAX_CAP / 4 - 9) {
            } else {
                panic!("isize::MAX + 1 should trigger an OOM!")
            }
        }
        if let Err(CapacityOverflow) = ten_u32s.try_reserve_exact(MAX_USIZE - 20) {
        } else {
            panic!("usize::MAX should trigger an overflow!")
        }
    }
}

#[test]
fn test_stable_pointers() {
    /// Pull an element from the iterator, then drop it.
    /// Useful to cover both the `next` and `drop` paths of an iterator.
    fn next_then_drop<I: Iterator>(mut i: I) {
        i.next().unwrap();
        drop(i);
    }

    // Test that, if we reserved enough space, adding and removing elements does not
    // invalidate references into the vector (such as `v0`).  This test also
    // runs in Miri, which would detect such problems.
    let mut v = Vec::with_capacity(128);
    v.push(13);

    // Laundering the lifetime -- we take care that `v` does not reallocate, so that's okay.
    let v0 = &mut v[0];
    let v0 = unsafe { &mut *(v0 as *mut _) };
    // Now do a bunch of things and occasionally use `v0` again to assert it is still valid.

    // Pushing/inserting and popping/removing
    v.push(1);
    v.push(2);
    v.insert(1, 1);
    assert_eq!(*v0, 13);
    v.remove(1);
    v.pop().unwrap();
    assert_eq!(*v0, 13);
    v.push(1);
    v.swap_remove(1);
    assert_eq!(v.len(), 2);
    v.swap_remove(1); // swap_remove the last element
    assert_eq!(*v0, 13);

    // Appending
    v.append(&mut vec![27, 19]);
    assert_eq!(*v0, 13);

    // Extending
    v.extend_from_slice(&[1, 2]);
    v.extend(&[1, 2]); // `slice::Iter` (with `T: Copy`) specialization
    v.extend(vec![2, 3]); // `vec::IntoIter` specialization
    v.extend(std::iter::once(3)); // `TrustedLen` specialization
    v.extend(std::iter::empty::<i32>()); // `TrustedLen` specialization with empty iterator
    v.extend(std::iter::once(3).filter(|_| true)); // base case
    v.extend(std::iter::once(&3)); // `cloned` specialization
    assert_eq!(*v0, 13);

    // Truncation
    v.truncate(2);
    assert_eq!(*v0, 13);

    // Resizing
    v.resize_with(v.len() + 10, || 42);
    assert_eq!(*v0, 13);
    v.resize_with(2, || panic!());
    assert_eq!(*v0, 13);

    // No-op reservation
    v.reserve(32);
    v.reserve_exact(32);
    assert_eq!(*v0, 13);

    // Partial draining
    v.resize_with(10, || 42);
    next_then_drop(v.drain(5..));
    assert_eq!(*v0, 13);

    // Splicing
    v.resize_with(10, || 42);
    next_then_drop(v.splice(5.., vec![1, 2, 3, 4, 5])); // empty tail after range
    assert_eq!(*v0, 13);
    next_then_drop(v.splice(5..8, vec![1])); // replacement is smaller than original range
    assert_eq!(*v0, 13);
    next_then_drop(v.splice(5..6, vec![1; 10].into_iter().filter(|_| true))); // lower bound not exact
    assert_eq!(*v0, 13);

    // Smoke test that would fire even outside Miri if an actual relocation happened.
    *v0 -= 13;
    assert_eq!(v[0], 0);
}

// https://github.com/rust-lang/rust/pull/49496 introduced specialization based on:
//
// ```
// unsafe impl<T: ?Sized> IsZero for *mut T {
//     fn is_zero(&self) -> bool {
//         (*self).is_null()
//     }
// }
// ```
//
// … to call `RawVec::with_capacity_zeroed` for creating `Vec<*mut T>`,
// which is incorrect for fat pointers since `<*mut T>::is_null` only looks at the data component.
// That is, a fat pointer can be “null” without being made entirely of zero bits.
#[test]
fn vec_macro_repeating_null_raw_fat_pointer() {
    let raw_dyn = &mut (|| ()) as &mut dyn Fn() as *mut dyn Fn();
    let vtable = dbg!(ptr_metadata(raw_dyn));
    let null_raw_dyn = ptr_from_raw_parts(std::ptr::null_mut(), vtable);
    assert!(null_raw_dyn.is_null());

    let vec = vec![null_raw_dyn; 1];
    dbg!(ptr_metadata(vec[0]));
    assert!(vec[0] == null_raw_dyn);

    // Polyfill for https://github.com/rust-lang/rfcs/pull/2580

    fn ptr_metadata(ptr: *mut dyn Fn()) -> *mut () {
        unsafe { std::mem::transmute::<*mut dyn Fn(), DynRepr>(ptr).vtable }
    }

    fn ptr_from_raw_parts(data: *mut (), vtable: *mut ()) -> *mut dyn Fn() {
        unsafe { std::mem::transmute::<DynRepr, *mut dyn Fn()>(DynRepr { data, vtable }) }
    }

    #[repr(C)]
    struct DynRepr {
        data: *mut (),
        vtable: *mut (),
    }
}

// This test will likely fail if you change the capacities used in
// `RawVec::grow_amortized`.
#[test]
fn test_push_growth_strategy() {
    // If the element size is 1, we jump from 0 to 8, then double.
    {
        let mut v1: Vec<u8> = vec![];
        assert_eq!(v1.capacity(), 0);

        for _ in 0..8 {
            v1.push(0);
            assert_eq!(v1.capacity(), 8);
        }

        for _ in 8..16 {
            v1.push(0);
            assert_eq!(v1.capacity(), 16);
        }

        for _ in 16..32 {
            v1.push(0);
            assert_eq!(v1.capacity(), 32);
        }

        for _ in 32..64 {
            v1.push(0);
            assert_eq!(v1.capacity(), 64);
        }
    }

    // If the element size is 2..=1024, we jump from 0 to 4, then double.
    {
        let mut v2: Vec<u16> = vec![];
        let mut v1024: Vec<[u8; 1024]> = vec![];
        assert_eq!(v2.capacity(), 0);
        assert_eq!(v1024.capacity(), 0);

        for _ in 0..4 {
            v2.push(0);
            v1024.push([0; 1024]);
            assert_eq!(v2.capacity(), 4);
            assert_eq!(v1024.capacity(), 4);
        }

        for _ in 4..8 {
            v2.push(0);
            v1024.push([0; 1024]);
            assert_eq!(v2.capacity(), 8);
            assert_eq!(v1024.capacity(), 8);
        }

        for _ in 8..16 {
            v2.push(0);
            v1024.push([0; 1024]);
            assert_eq!(v2.capacity(), 16);
            assert_eq!(v1024.capacity(), 16);
        }

        for _ in 16..32 {
            v2.push(0);
            v1024.push([0; 1024]);
            assert_eq!(v2.capacity(), 32);
            assert_eq!(v1024.capacity(), 32);
        }

        for _ in 32..64 {
            v2.push(0);
            v1024.push([0; 1024]);
            assert_eq!(v2.capacity(), 64);
            assert_eq!(v1024.capacity(), 64);
        }
    }

    // If the element size is > 1024, we jump from 0 to 1, then double.
    {
        let mut v1025: Vec<[u8; 1025]> = vec![];
        assert_eq!(v1025.capacity(), 0);

        for _ in 0..1 {
            v1025.push([0; 1025]);
            assert_eq!(v1025.capacity(), 1);
        }

        for _ in 1..2 {
            v1025.push([0; 1025]);
            assert_eq!(v1025.capacity(), 2);
        }

        for _ in 2..4 {
            v1025.push([0; 1025]);
            assert_eq!(v1025.capacity(), 4);
        }

        for _ in 4..8 {
            v1025.push([0; 1025]);
            assert_eq!(v1025.capacity(), 8);
        }

        for _ in 8..16 {
            v1025.push([0; 1025]);
            assert_eq!(v1025.capacity(), 16);
        }

        for _ in 16..32 {
            v1025.push([0; 1025]);
            assert_eq!(v1025.capacity(), 32);
        }

        for _ in 32..64 {
            v1025.push([0; 1025]);
            assert_eq!(v1025.capacity(), 64);
        }
    }
}
