`VecDeque` leaks remaining content when one destructor panics

[jonas-schievink]

STR:

use std::collections::VecDeque;

struct D(u8, bool);

impl Drop for D {
    fn drop(&mut self) {
        println!("Drop {}", self.0);
        if self.1 {
            panic!("panic in `drop`");
        }
    }
}

fn main() {
    let mut q = VecDeque::new();
    q.push_back(D(0, false));
    q.push_back(D(1, false));
    q.push_back(D(2, false));
    q.push_back(D(3, false));
    q.push_back(D(4, false));
    q.push_front(D(100, false));
    q.push_front(D(101, false));
    q.push_front(D(102, true));
}

Output:

Drop 102
thread 'main' panicked at 'panic in `drop`', test.rs:9:13
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace.
Drop 101
Drop 100

Caused by the Drop impl of VecDeque:

rust/src/liballoc/collections/vec_deque.rs

Lines 146 to 154 in 90b957a

	fn drop(&mut self) {
	let (front, back) = self.as_mut_slices();
	unsafe {
	// use drop for [T]
	ptr::drop_in_place(front);
	ptr::drop_in_place(back);
	}
	// RawVec handles deallocation
	}

Apparently drop_in_place will continue dropping elements when one destructor panics. That doesn't carry over to the second call, of course.

[jonas-schievink]

Same goes for vec_deque::IntoIter (it just contains a VecDeque, so would be fixed by fixing the drop impl).