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Using "mem::unitialized()" can lead to "Attempted to instantiate uninhabited type" #139
Description
The following code panics:
fn main() {
enum Void {}
let sv = smallvec::SmallVec::<[Void; 8]>::new();
}With:
thread 'main' panicked at 'Attempted to instantiate uninhabited type [main::Void; 8]', /rustc/ceb2512144d1fc26330e85fb9d41c22ba1866259/src/libcore/mem.rs:630:5
stack backtrace:
0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
at src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:39
1: std::sys_common::backtrace::_print
at src/libstd/sys_common/backtrace.rs:70
2: std::panicking::default_hook::{{closure}}
at src/libstd/sys_common/backtrace.rs:58
at src/libstd/panicking.rs:200
3: std::panicking::default_hook
at src/libstd/panicking.rs:215
4: std::panicking::rust_panic_with_hook
at src/libstd/panicking.rs:478
5: std::panicking::continue_panic_fmt
at src/libstd/panicking.rs:385
6: rust_begin_unwind
at src/libstd/panicking.rs:312
7: core::panicking::panic_fmt
at src/libcore/panicking.rs:85
8: core::panicking::panic
at src/libcore/panicking.rs:49
9: core::mem::uninitialized
at /rustc/ceb2512144d1fc26330e85fb9d41c22ba1866259/src/libcore/mem.rs:630
10: <smallvec::SmallVec<A>>::new
at /home/pierre/.cargo/registry/src/github.life-white.uk-1ecc6299db9ec823/smallvec-0.6.8/lib.rs:402
11: playpen::main
at src/main.rs:3
12: std::rt::lang_start::{{closure}}
at /rustc/ceb2512144d1fc26330e85fb9d41c22ba1866259/src/libstd/rt.rs:64
13: std::panicking::try::do_call
at src/libstd/rt.rs:49
at src/libstd/panicking.rs:297
14: __rust_maybe_catch_panic
at src/libpanic_unwind/lib.rs:92
15: std::rt::lang_start_internal
at src/libstd/panicking.rs:276
at src/libstd/panic.rs:388
at src/libstd/rt.rs:48
16: std::rt::lang_start
at /rustc/ceb2512144d1fc26330e85fb9d41c22ba1866259/src/libstd/rt.rs:64
17: main
18: __libc_start_main
19: _start
The culprit is here:
Line 402 in a775b5f
"Why would someone create a SmallVec of Void?" you may ask.
In my situation, the type (Void here) is a template parameter of one of my structs.
When the user uses a Void, the SmallVec will of course always remain empty. However creating an empty SmallVec shouldn't itself lead to a panic.
Activity
nox commentedon Feb 1, 2019
Relevant (IIRC): #126
RalfJung commentedon May 5, 2019
This also shows that e.g.
smallvec::SmallVec::<[bool; 8]>::new()causes UB -- it creates aboolthat is not properly initialized.Once rust-lang/rust#60445 lands, the
ManuallyDrophere should be replaced byMaybeUninit. That should help with these cases.Add a test for #139.
Auto merge of #170 - servo:test-139, r=SimonSapin
Add a test for servo#139.
Add a test for servo#139.
Add a test for servo#139.
Add a test for servo#139.