Regression in beta: unsafe-free, pure Rust pgm. with no deps segfaults

[osa1]

#[derive(Clone, Debug, PartialEq, Eq)]
pub enum Key {
    AltArrow(Arrow),
    Arrow(Arrow),
    Ctrl(char),
    Char(char),
    Esc,
}

#[derive(Clone, Debug, PartialEq, Eq)]
pub enum Arrow { Left, Right, Up, Down }

#[derive(Clone, Debug, PartialEq, Eq)]
pub enum Event {
    Key(Key),
    String(String),
    Resize,
    Unknown(Vec<u8>),
}

static XTERM_SINGLE_BYTES : [(u8, Event); 5] =
    [ (1,  Event::Key(Key::Ctrl('a'))),
      (5,  Event::Key(Key::Ctrl('e'))),
      (23, Event::Key(Key::Ctrl('w'))),
      (11, Event::Key(Key::Ctrl('k'))),
      (4,  Event::Key(Key::Ctrl('d'))),
    ];

fn main() {
    println!("{:?}", XTERM_SINGLE_BYTES);
}

(can be tested here: https://is.gd/EkJ3by)

When run with beta or nightly, this program segfaults.

I tried to simplify this a little bit, but my attempts either turned segfault into a stack overflow, or made it working. Here are some changes I've tried:

• I tried [(u8, char)] for XTERM_SINGLE_BYTES and it worked fine.
• I tried removing Event::Keys (e.g. [(u8, Key)]) and it worked.
• I removed some of the constructors from Event enum, most of the time the error turned into a stack overflow.

In my original program I'm iterating the array, and for the u8 part I'm getting random bytes instead of bytes I put in the array. I'm using rustc 1.13.0-nightly (70598e0 2016-09-03).

[durka]

Minimized a bit:

#[derive(Debug)]
pub enum Event {
    Key(u8),

    Resize,

    Unknown(Vec<u8>),
}

static XTERM_SINGLE_BYTES : [(u8, Event); 1] =
    [ (1,  Event::Resize)
    ];

fn main() {
    println!("{:?}", XTERM_SINGLE_BYTES);
}

This incorrectly prints [(1, Key(0))].

I wonder if it has something to do with the nullable pointer layout optimization, as the issue goes away if the Vec variant is removed.

[TimNN]

With -Z orbit, this was introduced between nightly-2016-05-08 and nightly-2016-05-09 (Changes).

(Edit: I missed a nightly in the original version of this comment.)

[osa1]

Thanks @TimNN, as a workaround until this is fixed I switched to nightly-2016-05-08 and it works nicely.

[durka]

In that case I'm suspicious of #33130 cc @eddyb

[TimNN]

The Vec is not necessary to reproduce,

#[derive(Debug)]
pub enum Event {
    Key(u8),
    Resize,
    Unknown(i16),
}

as long as the types wrapped are of different sizes.

Also, I can reproduce this only as long as the size of the integer used in the static is smaller than than the size of the larger "wrapped" integer (in this case, the wrapped integer is i16, so only i8 and u8 will reproduce this).

[arielb1]

Looks like missing alignment:

@_ZN8rust_out18XTERM_SINGLE_BYTES17heee0b00158a3d910E = internal constant { { i8, { i8, [3 x i8] } } } { { i8, { i8, [3 x i8] } } { i8 1, { i8, [3 x i8] } { i8 1, [3 x i8] undef } } }, align 2

[nagisa]

@arielb1 where did you get this? With original test case on play.rlo has align 8 for all stable, beta and nightly, which seems to be the expected value?

[arielb1]

The u16 variant by @TimNN. The problem is not the align 2 but the { i8, { i8, [3 x i8] } }