Open matthiaskrgr opened 5 months ago
cc @jswrenn
On it! Thanks for the report.
Further minimized:
#![feature(transmutability)]
mod assert {
use std::mem::{Assume, BikeshedIntrinsicFrom};
pub fn is_transmutable<Src, Dst>()
where
Dst: BikeshedIntrinsicFrom<Src, { Assume::NOTHING }>,
{
}
}
enum Lopsided {
Smol(()),
Lorg(bool),
}
fn should_pad_variants() {
assert::is_transmutable::<Lopsided, ()>();
}
The cause here is neat. Lopsided
here is niche optimizable, with its second variant being subject to niche optimization. Typically, a niche-optimized enum has one tagless variant, and zero or more tagged variants laid out in the usual manner: the tag is placed, and then the rest of the fields follow. But #[rustc_layout(debug)]
reveals that's not what happens here. Because ()
is a ZST, ()
is placed at offset 0
, rather than 1
(following the tag). In other words: the tag is co-located with the field. This produces an ICE, because our assumption that fields follow tag is violated (a checked sub panics).
@rustbot claim
auto-reduced (treereduce-rust):
original code
original: ````rust //! The variants of an enum must be padded with uninit bytes such that they have //! the same length (in bytes). #![crate_type = "lib"] #![feature(transmutability)] #![allow(dead_code)] mod assert { use std::mem::{Assume, BikeshedIntrinsicFrom}; pub fn is_transmutable()
where
Dst: BikeshedIntrinsicFrom
{}
}
#[derive(Clone, Copy)]
#[repr(C)] struct Zst;
#[derive(Clone, Copy)]
#[repr(u8)] enum V0 { V = 0 }
#[derive(Clone, Copy)]
#[repr(u8)] enum V2 { V = 2 }
#[repr(transmutability)]
enum Lopsided {
Smol(Zst),
Lorg(V0),
}
#[repr(C)] struct Src(V0, Zst V2);
#[repr(C)] struct Dst(Lopsided, V2);
fn should_pad_variants() {
// If the implementation (incorrectly) fails to pad `Lopsided::Smol` with
// an uninitialized byte, this transmutation might be (wrongly) accepted:
assert::is_transmutable::(); //~ ERROR cannot be safely transmuted
}
````
Version information
Command:
/home/matthias/.rustup/toolchains/master/bin/rustc
Program output
``` error[E0412]: cannot find type `Src` in this scope --> /tmp/icemaker_global_tempdir.7GMaangOEeD3/rustc_testrunner_tmpdir_reporting.sKS3rJHCTOdj/mvce.rs:33:31 | 33 | assert::is_transmutable::();
| ^^^ not found in this scope
|
help: you might be missing a type parameter
|
32 | fn should_pad_variants() {
| +++++
warning: unused import: `Assume`
--> /tmp/icemaker_global_tempdir.7GMaangOEeD3/rustc_testrunner_tmpdir_reporting.sKS3rJHCTOdj/mvce.rs:2:20
|
2 | use std::mem::{Assume, BikeshedIntrinsicFrom};
| ^^^^^^
|
= note: `#[warn(unused_imports)]` on by default
error[E0601]: `main` function not found in crate `mvce`
--> /tmp/icemaker_global_tempdir.7GMaangOEeD3/rustc_testrunner_tmpdir_reporting.sKS3rJHCTOdj/mvce.rs:34:2
|
34 | }
| ^ consider adding a `main` function to `/tmp/icemaker_global_tempdir.7GMaangOEeD3/rustc_testrunner_tmpdir_reporting.sKS3rJHCTOdj/mvce.rs`
error[E0658]: use of unstable library feature 'transmutability'
--> /tmp/icemaker_global_tempdir.7GMaangOEeD3/rustc_testrunner_tmpdir_reporting.sKS3rJHCTOdj/mvce.rs:2:20
|
2 | use std::mem::{Assume, BikeshedIntrinsicFrom};
| ^^^^^^
|
= note: see issue #99571 for more information
= help: add `#![feature(transmutability)]` to the crate attributes to enable
= note: this compiler was built on 2024-04-09; consider upgrading it if it is out of date
error[E0658]: use of unstable library feature 'transmutability'
--> /tmp/icemaker_global_tempdir.7GMaangOEeD3/rustc_testrunner_tmpdir_reporting.sKS3rJHCTOdj/mvce.rs:2:28
|
2 | use std::mem::{Assume, BikeshedIntrinsicFrom};
| ^^^^^^^^^^^^^^^^^^^^^
|
= note: see issue #99571 for more information
= help: add `#![feature(transmutability)]` to the crate attributes to enable
= note: this compiler was built on 2024-04-09; consider upgrading it if it is out of date
error[E0658]: use of unstable library feature 'transmutability'
--> /tmp/icemaker_global_tempdir.7GMaangOEeD3/rustc_testrunner_tmpdir_reporting.sKS3rJHCTOdj/mvce.rs:6:14
|
6 | Dst: BikeshedIntrinsicFrom,
| ^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: see issue #99571 for more information
= help: add `#![feature(transmutability)]` to the crate attributes to enable
= note: this compiler was built on 2024-04-09; consider upgrading it if it is out of date
thread 'rustc' panicked at /rustc/033becf83c62814357f4810db149471db46ab816/compiler/rustc_abi/src/lib.rs:581:13:
Size::sub: 0 - 1 would result in negative size
stack backtrace:
0: 0x79db92be6885 - std::backtrace_rs::backtrace::libunwind::trace::he2880c2699337794
at /rustc/033becf83c62814357f4810db149471db46ab816/library/std/src/../../backtrace/src/backtrace/libunwind.rs:105:5
1: 0x79db92be6885 - std::backtrace_rs::backtrace::trace_unsynchronized::h460ebc9cd0eb6331
at /rustc/033becf83c62814357f4810db149471db46ab816/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
2: 0x79db92be6885 - std::sys_common::backtrace::_print_fmt::h47b746c0604572c3
at /rustc/033becf83c62814357f4810db149471db46ab816/library/std/src/sys_common/backtrace.rs:68:5
3: 0x79db92be6885 - ::fmt::ha907b996746f56a0
at /rustc/033becf83c62814357f4810db149471db46ab816/library/std/src/sys_common/backtrace.rs:44:22
4: 0x79db92c35abb - core::fmt::rt::Argument::fmt::hfe22b646b1687193
at /rustc/033becf83c62814357f4810db149471db46ab816/library/core/src/fmt/rt.rs:142:9
5: 0x79db92c35abb - core::fmt::write::h6b4a267d08f3d00d
at /rustc/033becf83c62814357f4810db149471db46ab816/library/core/src/fmt/mod.rs:1153:17
6: 0x79db92bdb3ff - std::io::Write::write_fmt::h0abdd14d11c1702a
at /rustc/033becf83c62814357f4810db149471db46ab816/library/std/src/io/mod.rs:1843:15
7: 0x79db92be665e - std::sys_common::backtrace::_print::hbeb8c9c7793a4a1e
at /rustc/033becf83c62814357f4810db149471db46ab816/library/std/src/sys_common/backtrace.rs:47:5
8: 0x79db92be665e - std::sys_common::backtrace::print::h6ca4866d684d9b00
at /rustc/033becf83c62814357f4810db149471db46ab816/library/std/src/sys_common/backtrace.rs:34:9
9: 0x79db92be9159 - std::panicking::default_hook::{{closure}}::h33647e3098e0b657
10: 0x79db92be8e75 - std::panicking::default_hook::ha6320bcd5d0e9cc8
at /rustc/033becf83c62814357f4810db149471db46ab816/library/std/src/panicking.rs:291:9
11: 0x79db8f46649f - std[5013708940097fa8]::panicking::update_hook::>::{closure#0}
12: 0x79db92be985c - as core::ops::function::Fn>::call::hf428354f3713bf5b
at /rustc/033becf83c62814357f4810db149471db46ab816/library/alloc/src/boxed.rs:2032:9
13: 0x79db92be985c - std::panicking::rust_panic_with_hook::h0014da0b7030d171
at /rustc/033becf83c62814357f4810db149471db46ab816/library/std/src/panicking.rs:792:13
14: 0x79db92be9606 - std::panicking::begin_panic_handler::{{closure}}::h639e3e9de7a3e2e4
at /rustc/033becf83c62814357f4810db149471db46ab816/library/std/src/panicking.rs:657:13
15: 0x79db92be6d49 - std::sys_common::backtrace::__rust_end_short_backtrace::h66ed5715b81f24d6
at /rustc/033becf83c62814357f4810db149471db46ab816/library/std/src/sys_common/backtrace.rs:171:18
16: 0x79db92be9337 - rust_begin_unwind
at /rustc/033becf83c62814357f4810db149471db46ab816/library/std/src/panicking.rs:645:5
17: 0x79db92c31f56 - core::panicking::panic_fmt::h2fea69f54f6dc828
at /rustc/033becf83c62814357f4810db149471db46ab816/library/core/src/panicking.rs:72:14
18: 0x79db8fffc247 - ::sub::{closure#0}
19: 0x79db9000cb17 - >::from_variant
20: 0x79db9000bffa - >::from_enum
21: 0x79db9000c756 - >::from_variant
22: 0x79db9000b43f - >::from_struct
23: 0x79db9000f833 - ::is_transmutable
24: 0x79db910150a5 - ::confirm_candidate
25: 0x79db8d4ba166 - ::evaluate_candidate
26: 0x79db9115a88c - ::evaluate_trait_predicate_recursively
27: 0x79db90f0f668 - ::evaluation_probe::<::evaluate_root_obligation::{closure#0}>
28: 0x79db90f0dc9a - rustc_traits[ccae72c98d3fa03e]::evaluate_obligation::evaluate_obligation
29: 0x79db90f0d62b - rustc_query_impl[a13915abec574cc4]::plumbing::__rust_begin_short_backtrace::>
30: 0x79db90f0cb92 - rustc_query_system[37cb0ad7182a86b8]::query::plumbing::try_execute_query::>, rustc_middle[867c8a7f7f3067fc]::query::erase::Erased<[u8; 2usize]>>, false, false, false>, rustc_query_impl[a13915abec574cc4]::plumbing::QueryCtxt, false>
31: 0x79db90f0c7da - rustc_query_impl[a13915abec574cc4]::query_impl::evaluate_obligation::get_query_non_incr::__rust_end_short_backtrace
32: 0x79db8d404081 - ::process_obligation
33: 0x79db9080d663 - >::process_obligations::
34: 0x79db90fe11bf - ::check_argument_types
35: 0x79db90fd71eb - ::check_call
36: 0x79db9128d159 - ::check_expr_with_expectation_and_args
37: 0x79db91287a26 - ::check_block_with_expected
38: 0x79db9128d63d - ::check_expr_with_expectation_and_args
39: 0x79db909ee20e - rustc_hir_typeck[90aadd5cc69e56e5]::check::check_fn
40: 0x79db909e4749 - rustc_hir_typeck[90aadd5cc69e56e5]::typeck
41: 0x79db909e4109 - rustc_query_impl[a13915abec574cc4]::plumbing::__rust_begin_short_backtrace::>
42: 0x79db909d0871 - rustc_query_system[37cb0ad7182a86b8]::query::plumbing::try_execute_query::>, false, false, false>, rustc_query_impl[a13915abec574cc4]::plumbing::QueryCtxt, false>
43: 0x79db909cf18c - rustc_query_impl[a13915abec574cc4]::query_impl::typeck::get_query_non_incr::__rust_end_short_backtrace
44: 0x79db909ced54 - ::par_body_owners::::{closure#0}
45: 0x79db909cda1f - rustc_hir_analysis[341fcfcfa163e951]::check_crate
46: 0x79db910ee93a - rustc_interface[791da96d69a7cf4c]::passes::analysis
47: 0x79db910ee495 - rustc_query_impl[a13915abec574cc4]::plumbing::__rust_begin_short_backtrace::>
48: 0x79db915fa6a5 - rustc_query_system[37cb0ad7182a86b8]::query::plumbing::try_execute_query::>, false, false, false>, rustc_query_impl[a13915abec574cc4]::plumbing::QueryCtxt, false>
49: 0x79db915fa409 - rustc_query_impl[a13915abec574cc4]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
50: 0x79db91480cd4 - rustc_interface[791da96d69a7cf4c]::interface::run_compiler::, rustc_driver_impl[83e8eb7d3795c9f9]::run_compiler::{closure#0}>::{closure#0}
51: 0x79db9154deff - std[5013708940097fa8]::sys_common::backtrace::__rust_begin_short_backtrace::, rustc_driver_impl[83e8eb7d3795c9f9]::run_compiler::{closure#0}>::{closure#0}, core[b815557cbe89e06]::result::Result<(), rustc_span[ef049dfdad08a076]::ErrorGuaranteed>>::{closure#0}, core[b815557cbe89e06]::result::Result<(), rustc_span[ef049dfdad08a076]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[b815557cbe89e06]::result::Result<(), rustc_span[ef049dfdad08a076]::ErrorGuaranteed>>
52: 0x79db9154dcee - <::spawn_unchecked_, rustc_driver_impl[83e8eb7d3795c9f9]::run_compiler::{closure#0}>::{closure#0}, core[b815557cbe89e06]::result::Result<(), rustc_span[ef049dfdad08a076]::ErrorGuaranteed>>::{closure#0}, core[b815557cbe89e06]::result::Result<(), rustc_span[ef049dfdad08a076]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[b815557cbe89e06]::result::Result<(), rustc_span[ef049dfdad08a076]::ErrorGuaranteed>>::{closure#1} as core[b815557cbe89e06]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
53: 0x79db92bf328b - as core::ops::function::FnOnce>::call_once::h53814b1241345312
at /rustc/033becf83c62814357f4810db149471db46ab816/library/alloc/src/boxed.rs:2018:9
54: 0x79db92bf328b - as core::ops::function::FnOnce>::call_once::h68f33d2823fce7a0
at /rustc/033becf83c62814357f4810db149471db46ab816/library/alloc/src/boxed.rs:2018:9
55: 0x79db92bf328b - std::sys::pal::unix::thread::Thread::new::thread_start::h5c5183b404e56855
at /rustc/033becf83c62814357f4810db149471db46ab816/library/std/src/sys/pal/unix/thread.rs:108:17
56: 0x79db9299155a -
57: 0x79db92a0ea3c -
58: 0x0 -
error: the compiler unexpectedly panicked. this is a bug.
note: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md
note: rustc 1.79.0-nightly (033becf83 2024-04-09) running on x86_64-unknown-linux-gnu
query stack during panic:
#0 [evaluate_obligation] evaluating trait selection obligation `Dst: core::mem::transmutability::BikeshedIntrinsicFrom<{type error}, core::mem::transmutability::Assume { alignment: false, lifetimes: false, safety: false, validity: false }>`
#1 [typeck] type-checking `should_pad_variants`
#2 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to 5 previous errors; 1 warning emitted
Some errors have detailed explanations: E0412, E0601, E0658.
For more information about an error, try `rustc --explain E0412`.
```