rustc should not suggest #![feature(core_intrinsics)]

Rust beginner here. I was trying something out on the Playground, turns out I didn't understand how to use wrapping_add correctly; but following a sequence of suggested fixes from the compiler I arrived at the below, which gives two internal compiler errors. I asked on Discord and was told it is worth reporting it here, even though this code is incorrect and uses an unstable library feature.

Code

#![feature(core_intrinsics)]
use std::intrinsics::wrapping_add;

#[derive(Clone, Copy)]
struct WrapInt8 {
    value: u8
}

impl std::ops::Add for WrapInt8 {
    type Output = WrapInt8;
    fn add(self, other: WrapInt8) -> WrapInt8 {
        wrapping_add(self, other)
    }
}

fn main() {
    let p = WrapInt8 { value: 123 };
    let q = WrapInt8 { value: 234 };
    println!("{}", (p + q).value);
}

Error output

   Compiling playground v0.0.1 (/playground)
error: internal compiler error: no errors encountered even though `delay_span_bug` issued

error: internal compiler error: broken MIR in Item(WithOptConstParam { did: DefId(0:8 ~ playground[3faf]::{impl#0}::add), const_param_did: None }) (end of phase transition to Optimized) at bb0[2]:
                                Cannot perform arithmetic on type WrapInt8
  --> src/main.rs:12:9
   |
12 |         wrapping_add(self, other)
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: delayed at compiler/rustc_const_eval/src/transform/validate.rs:127:36

thread 'rustc' panicked at 'Box<dyn Any>', compiler/rustc_errors/src/lib.rs:1368:13
stack backtrace:
   0:     0x7f216626ffcd - std::backtrace_rs::backtrace::libunwind::trace::h9dd319c001cd5d5b
                               at /rustc/ebbcbfc236ced21d5e6a92269edb704692ff26b8/library/std/src/../../backtrace/src/backtrace/libunwind.rs:93:5
   1:     0x7f216626ffcd - std::backtrace_rs::backtrace::trace_unsynchronized::h5cdb9413f7b7f703
                               at /rustc/ebbcbfc236ced21d5e6a92269edb704692ff26b8/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f216626ffcd - std::sys_common::backtrace::_print_fmt::h62e01fe71d2f0609
                               at /rustc/ebbcbfc236ced21d5e6a92269edb704692ff26b8/library/std/src/sys_common/backtrace.rs:66:5
   3:     0x7f216626ffcd - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::hb568664ce7d28696
                               at /rustc/ebbcbfc236ced21d5e6a92269edb704692ff26b8/library/std/src/sys_common/backtrace.rs:45:22
   4:     0x7f21662cbe5c - core::fmt::write::hff09181fc8f150c2
                               at /rustc/ebbcbfc236ced21d5e6a92269edb704692ff26b8/library/core/src/fmt/mod.rs:1196:17
   5:     0x7f21662616c1 - std::io::Write::write_fmt::h77801493f17dbb5a
                               at /rustc/ebbcbfc236ced21d5e6a92269edb704692ff26b8/library/std/src/io/mod.rs:1654:15
   6:     0x7f2166272cb5 - std::sys_common::backtrace::_print::hace3cc1f256ece45
                               at /rustc/ebbcbfc236ced21d5e6a92269edb704692ff26b8/library/std/src/sys_common/backtrace.rs:48:5
   7:     0x7f2166272cb5 - std::sys_common::backtrace::print::hc1b81d3f2867b83b
                               at /rustc/ebbcbfc236ced21d5e6a92269edb704692ff26b8/library/std/src/sys_common/backtrace.rs:35:9
   8:     0x7f2166272cb5 - std::panicking::default_hook::{{closure}}::he802b1e81f85775c
                               at /rustc/ebbcbfc236ced21d5e6a92269edb704692ff26b8/library/std/src/panicking.rs:295:22
   9:     0x7f21662729d6 - std::panicking::default_hook::h57b0d510bf2c9fe7
                               at /rustc/ebbcbfc236ced21d5e6a92269edb704692ff26b8/library/std/src/panicking.rs:314:9
  10:     0x7f2166a3c211 - rustc_driver[8a2d58f6f4bf431a]::DEFAULT_HOOK::{closure#0}::{closure#0}
  11:     0x7f216627338a - std::panicking::rust_panic_with_hook::hdd373bc6c22fa56f
                               at /rustc/ebbcbfc236ced21d5e6a92269edb704692ff26b8/library/std/src/panicking.rs:702:17
  12:     0x7f2167bdb181 - std[aa967257b9f8f73b]::panicking::begin_panic::<rustc_errors[1ed68885dba1d6d1]::ExplicitBug>::{closure#0}
  13:     0x7f2167bd9e06 - std[aa967257b9f8f73b]::sys_common::backtrace::__rust_end_short_backtrace::<std[aa967257b9f8f73b]::panicking::begin_panic<rustc_errors[1ed68885dba1d6d1]::ExplicitBug>::{closure#0}, !>
  14:     0x7f2167bedd56 - std[aa967257b9f8f73b]::panicking::begin_panic::<rustc_errors[1ed68885dba1d6d1]::ExplicitBug>
  15:     0x7f2167bf1ec6 - std[aa967257b9f8f73b]::panic::panic_any::<rustc_errors[1ed68885dba1d6d1]::ExplicitBug>
  16:     0x7f21694638e1 - <rustc_errors[1ed68885dba1d6d1]::HandlerInner as core[8467f2214112d7a4]::ops::drop::Drop>::drop
  17:     0x7f2168bcf7a8 - core[8467f2214112d7a4]::ptr::drop_in_place::<rustc_session[f5a33ef05da8b8fa]::parse::ParseSess>
  18:     0x7f2168bd1ac3 - <alloc[e5cd0633e65a6c1f]::rc::Rc<rustc_session[f5a33ef05da8b8fa]::session::Session> as core[8467f2214112d7a4]::ops::drop::Drop>::drop
  19:     0x7f2168bce36d - core[8467f2214112d7a4]::ptr::drop_in_place::<rustc_interface[b93c8180971df832]::interface::Compiler>
  20:     0x7f2168bcdd94 - rustc_span[4bbade9624b8160a]::with_source_map::<core[8467f2214112d7a4]::result::Result<(), rustc_errors[1ed68885dba1d6d1]::ErrorGuaranteed>, rustc_interface[b93c8180971df832]::interface::create_compiler_and_run<core[8467f2214112d7a4]::result::Result<(), rustc_errors[1ed68885dba1d6d1]::ErrorGuaranteed>, rustc_driver[8a2d58f6f4bf431a]::run_compiler::{closure#1}>::{closure#1}>
  21:     0x7f2168bba454 - rustc_interface[b93c8180971df832]::interface::create_compiler_and_run::<core[8467f2214112d7a4]::result::Result<(), rustc_errors[1ed68885dba1d6d1]::ErrorGuaranteed>, rustc_driver[8a2d58f6f4bf431a]::run_compiler::{closure#1}>
  22:     0x7f2168ba4792 - <scoped_tls[6dc72d687799c0be]::ScopedKey<rustc_span[4bbade9624b8160a]::SessionGlobals>>::set::<rustc_interface[b93c8180971df832]::interface::run_compiler<core[8467f2214112d7a4]::result::Result<(), rustc_errors[1ed68885dba1d6d1]::ErrorGuaranteed>, rustc_driver[8a2d58f6f4bf431a]::run_compiler::{closure#1}>::{closure#0}, core[8467f2214112d7a4]::result::Result<(), rustc_errors[1ed68885dba1d6d1]::ErrorGuaranteed>>
  23:     0x7f2168bbbb3f - std[aa967257b9f8f73b]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[b93c8180971df832]::util::run_in_thread_pool_with_globals<rustc_interface[b93c8180971df832]::interface::run_compiler<core[8467f2214112d7a4]::result::Result<(), rustc_errors[1ed68885dba1d6d1]::ErrorGuaranteed>, rustc_driver[8a2d58f6f4bf431a]::run_compiler::{closure#1}>::{closure#0}, core[8467f2214112d7a4]::result::Result<(), rustc_errors[1ed68885dba1d6d1]::ErrorGuaranteed>>::{closure#0}, core[8467f2214112d7a4]::result::Result<(), rustc_errors[1ed68885dba1d6d1]::ErrorGuaranteed>>
  24:     0x7f2168bbbc79 - <<std[aa967257b9f8f73b]::thread::Builder>::spawn_unchecked_<rustc_interface[b93c8180971df832]::util::run_in_thread_pool_with_globals<rustc_interface[b93c8180971df832]::interface::run_compiler<core[8467f2214112d7a4]::result::Result<(), rustc_errors[1ed68885dba1d6d1]::ErrorGuaranteed>, rustc_driver[8a2d58f6f4bf431a]::run_compiler::{closure#1}>::{closure#0}, core[8467f2214112d7a4]::result::Result<(), rustc_errors[1ed68885dba1d6d1]::ErrorGuaranteed>>::{closure#0}, core[8467f2214112d7a4]::result::Result<(), rustc_errors[1ed68885dba1d6d1]::ErrorGuaranteed>>::{closure#1} as core[8467f2214112d7a4]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  25:     0x7f216627d2a3 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hf3233b13e94151c3
                               at /rustc/ebbcbfc236ced21d5e6a92269edb704692ff26b8/library/alloc/src/boxed.rs:1872:9
  26:     0x7f216627d2a3 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h4e8ef0a8db850d9e
                               at /rustc/ebbcbfc236ced21d5e6a92269edb704692ff26b8/library/alloc/src/boxed.rs:1872:9
  27:     0x7f216627d2a3 - std::sys::unix::thread::Thread::new::thread_start::haa7458da1d6aafbd
                               at /rustc/ebbcbfc236ced21d5e6a92269edb704692ff26b8/library/std/src/sys/unix/thread.rs:108:17
  28:     0x7f21661a3609 - start_thread
  29:     0x7f21660c6133 - clone
  30:                0x0 - <unknown>

note: 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 1.63.0-nightly (ebbcbfc23 2022-05-27) running on x86_64-unknown-linux-gnu

note: compiler flags: --crate-type bin -C embed-bitcode=no -C codegen-units=1 -C debuginfo=2

note: some of the compiler flags provided by cargo are hidden

query stack during panic:
end of query stack
error: could not compile `playground`

@JakobDegen

searched nightlies: from nightly-2022-03-01 to nightly-2022-05-28
regressed nightly: nightly-2022-04-13
searched commit range: 90ca447...52ca603
regressed commit: 2a83fbc

bisected with cargo-bisect-rustc v0.6.2

Host triple: x86_64-unknown-linux-gnu
Reproduce with:

cargo bisect-rustc --start=2022-03-01 --end=2022-05-28 --regress=ice

Makes sense to fail in #95320, cc @JakobDegen. Maybe this should be a hard error instead of a delayed bug?

Thanks for the report!

Before that PR, this:

#![feature(core_intrinsics)]

pub fn add(a: bool, b: bool) -> bool {
    std::intrinsics::wrapping_add(a, b)
}

just happily compiled, and this:

#![feature(core_intrinsics)]
use std::intrinsics::wrapping_add;

#[derive(Clone, Copy)]
struct WrapInt8 {
    value: u8,
    value2: u16,
}

impl std::ops::Add for WrapInt8 {
    type Output = WrapInt8;
    fn add(self, other: WrapInt8) -> WrapInt8 {
        wrapping_add(self, other)
    }
}

fn main() {
    let p = WrapInt8 { value: 1, value2: 2 };
    let q = WrapInt8 { value: 3, value2: 4 };
    println!("{}", (p + q).value);
}

already ICEd, so I don't think this is a regression. I'm tempted to say that we shouldn't bother trying to fix this, and that #![feature(core_intrinsics)] is not "supported" in the sense that this bug wants it to be. I'm not sure what the procedure is for making a decision on this though.

Edit: Maybe the actual bug here is that we recommend #![feature(core_intrinsics)] in diagnostics?

Maybe the actual bug here is that we recommend #![feature(core_intrinsics)] in diagnostics?

I would agree with this. It probably makes sense to exclude std::intrinsics and core::intrinsics from suggested fixes, too.

add 4 ices

I agree that ICEing for this is actually pretty expected -- intrinsics are super-internal, and ICEing for misuse is basically fine.

👍 to seeing if we can make sure not to suggest core_intrinsics the feature, or really anything with the extern "rust-intrinsic" ABI called via the intrinsics module. (Sadly there are some stable things with that ABI.)

Maybe for the things that are stable we can have them emit warnings/errors pointing to the stable versions? Since this example really wants u8::wrapping_add, not the intrinsic. (Well, really it wants num::Wrapping<u8>, but we're probably not able to be that smart about it.)

We might also want to change this message if the crate uses the core_intrinsic feature:

note: the compiler unexpectedly panicked. this is a bug.

ICEs are not always bugs when intrinsics are used directly.

🤔

note: the compiler expectedly panicked. this is not a bug.

Unfortunately there's no label for "inviting Rust programmers to see a cask of Amontillado".

Rollup merge of rust-lang#128173 - compiler-errors:misused-intrinsics…

Reopening, since

Maybe the actual bug here is that we recommend #![feature(core_intrinsics)] in diagnostics?

Though... on playground I do find this recommendation quite handy, when I have to craft some code that actually wants to call intrinsics. And we do emit this now:

warning: the feature `core_intrinsics` is internal to the compiler or standard library
 --> src/main.rs:1:12
  |
1 | #![feature(core_intrinsics)]
  |            ^^^^^^^^^^^^^^^
  |
  = note: using it is strongly discouraged
  = note: `#[warn(internal_features)]` on by default

But we also still say this, which we probably shouldn't:

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

Rollup merge of rust-lang#128202 - compiler-errors:internal-lib-featu…

Unrolled build for rust-lang#128202

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rustc should not suggest `#![feature(core_intrinsics)]` #97501

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rustc should not suggest #![feature(core_intrinsics)] #97501

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compiler-errors commented on May 29, 2022

JakobDegen commented on May 29, 2022

kaya3 commented on May 29, 2022

scottmcm commented on May 30, 2022

RalfJung commented on Jun 3, 2022

workingjubilee commented on Mar 11, 2023

RalfJung commented on Jul 25, 2024

RalfJung commented on Jul 25, 2024

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rustc should not suggest `#![feature(core_intrinsics)]` #97501