ICE: feature(test), requires two tests in lib

[is8ac]

To ICE, both tests must be present. Also, if the code compiles successfully, the cache is poisoned. Until cargo clean is run, all future runs will compile successfully, even once the offending code is reintroduced. Also, this only ICEs as a lib, not as a binary.

Steps to reproduce:

• cargo test # ICE
• remove test1 or test2
• cargo test # compiles
• add the test back, such that there are now two tests as before.
• cargo test # still compiles
• cargo clean
• cargo test # ICE

I have been unable to reduce the code further. My apologies for its length. The original was much worse.

Code

lib.rs:

#![feature(test)]

pub trait Corge<T> {
    type Fred;
}

impl Corge<u8> for () {
    type Fred = u32;
}

pub trait Waldo {
    type Quax;
}

impl Waldo for u32 {
    type Quax = u8;
}

pub trait Grault
where
    (): Corge<Self::Thud>,
{
    type Thud;
    fn bar(_: <() as Corge<Self::Thud>>::Fred) {}
}

impl<T> Grault for T
where
    T: Waldo,
    (): Corge<T::Quax>,
    <() as Corge<T::Quax>>::Fred: Waldo,
{
    type Thud = u8;
}

pub trait Plugh<I> {
    fn baz();
}

#[derive(Copy, Clone, Debug)]
pub struct Qiz<T> {
    foo: T,
}

impl<T> Plugh<<() as Corge<T::Thud>>::Fred> for Qiz<T>
where
    T: Grault,
    (): Corge<T::Thud>,
{
    fn baz() {}
}

#[cfg(test)]
mod tests {
    use super::{Grault, Plugh, Qiz};
    extern crate test;

    #[test]
    fn test1() {
        <u32 as Grault>::bar(0u32);
    }

    #[test]
    fn test2() {
        <Qiz<u32> as Plugh<u32>>::baz();
    }
}

Meta

rustc --version --verbose:

rustc 1.49.0-nightly (ffa2e7ae8 2020-10-24)
binary: rustc
commit-hash: ffa2e7ae8fbf9badc035740db949b9dae271c29f
commit-date: 2020-10-24
host: x86_64-unknown-linux-gnu
release: 1.49.0-nightly
LLVM version: 11.0

Error output

$ cargo test --lib
   Compiling icedemo v0.1.0 (/home/isaac/go/src/github.ibm.com/ifleonar/bitnn/ice_demo)
thread 'rustc' panicked at 'called `Result::unwrap()` on an `Err` value: ErrorReported', compiler/rustc_mir/src/monomorphize/collector.rs:746:84
stack backtrace:
   0: rust_begin_unwind
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/std/src/panicking.rs:483:5
   1: core::panicking::panic_fmt
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/core/src/panicking.rs:85:14
   2: core::option::expect_none_failed
             at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/core/src/option.rs:1268:5
   3: <rustc_mir::monomorphize::collector::MirNeighborCollector as rustc_middle::mir::visit::Visitor>::visit_terminator
   4: rustc_mir::monomorphize::collector::collect_neighbours
   5: rustc_mir::monomorphize::collector::collect_items_rec
   6: rustc_mir::monomorphize::collector::collect_items_rec
   7: rustc_mir::monomorphize::collector::collect_items_rec
   8: rustc_session::utils::<impl rustc_session::session::Session>::time
   9: rustc_mir::monomorphize::collector::collect_crate_mono_items
  10: rustc_mir::monomorphize::partitioning::collect_and_partition_mono_items
  11: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::collect_and_partition_mono_items>::compute
  12: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  13: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  14: rustc_data_structures::stack::ensure_sufficient_stack
  15: rustc_query_system::query::plumbing::get_query_impl
  16: rustc_codegen_ssa::base::codegen_crate
  17: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_ssa::traits::backend::CodegenBackend>::codegen_crate
  18: rustc_interface::passes::QueryContext::enter
  19: rustc_interface::queries::Queries::ongoing_codegen
  20: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
  21: rustc_span::with_source_map
  22: rustc_interface::interface::create_compiler_and_run
  23: scoped_tls::ScopedKey<T>::set
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

error: internal compiler error: unexpected panic

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 1.49.0-nightly (ffa2e7ae8 2020-10-24) running on x86_64-unknown-linux-gnu

note: compiler flags: -C embed-bitcode=no -C debuginfo=2 -C incremental

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

query stack during panic:
#0 [collect_and_partition_mono_items] collect_and_partition_mono_items
end of query stack
error: internal compiler error: Encountered error `Unimplemented` selecting `Binder(<Qiz<u32> as Plugh<u32>>)` during codegen
  |
  = note: delayed at compiler/rustc_trait_selection/src/traits/codegen.rs:68:32

thread 'rustc' panicked at 'no errors encountered even though `delay_span_bug` issued', compiler/rustc_errors/src/lib.rs:961:13
stack backtrace:
   0:     0x7fc78a054a20 - std::backtrace_rs::backtrace::libunwind::trace::h303a626d53553a64
                               at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/std/src/../../backtrace/src/backtrace/libunwind.rs:100:5
   1:     0x7fc78a054a20 - std::backtrace_rs::backtrace::trace_unsynchronized::h6abb882733c3f18c
                               at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7fc78a054a20 - std::sys_common::backtrace::_print_fmt::h57829321f1d9217a
                               at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/std/src/sys_common/backtrace.rs:67:5
   3:     0x7fc78a054a20 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h400b66a054640aac
                               at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/std/src/sys_common/backtrace.rs:46:22
   4:     0x7fc78a0c3e9c - core::fmt::write::h1857a60b204f1b6a
                               at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/core/src/fmt/mod.rs:1076:17
   5:     0x7fc78a046642 - std::io::Write::write_fmt::h6453b28c8b27c6ea
                               at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/std/src/io/mod.rs:1516:15
   6:     0x7fc78a0599d5 - std::sys_common::backtrace::_print::h15cc4b3923cc9bc0
                               at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/std/src/sys_common/backtrace.rs:49:5
   7:     0x7fc78a0599d5 - std::sys_common::backtrace::print::h953c7be178c0674d
                               at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/std/src/sys_common/backtrace.rs:36:9
   8:     0x7fc78a0599d5 - std::panicking::default_hook::{{closure}}::h635d667f571198f0
                               at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/std/src/panicking.rs:208:50
   9:     0x7fc78a059678 - std::panicking::default_hook::h3bc2efb48060abaa
                               at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/std/src/panicking.rs:227:9
  10:     0x7fc78a922618 - rustc_driver::report_ice::hbf1325c7565687ba
  11:     0x7fc78a05a216 - std::panicking::rust_panic_with_hook::h887eb0c89f46b8b2
                               at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/std/src/panicking.rs:581:17
  12:     0x7fc78a059d99 - std::panicking::begin_panic_handler::{{closure}}::hf0d3f46d37dd3bc1
                               at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/std/src/panicking.rs:484:9
  13:     0x7fc78a054ebc - std::sys_common::backtrace::__rust_end_short_backtrace::h4bce8b52717576e3
                               at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/std/src/sys_common/backtrace.rs:141:18
  14:     0x7fc78a059d59 - rust_begin_unwind
                               at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/std/src/panicking.rs:483:5
  15:     0x7fc78a059d0b - std::panicking::begin_panic_fmt::h53297a84a5b19714
                               at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/std/src/panicking.rs:437:5
  16:     0x7fc78d9056b1 - rustc_errors::HandlerInner::flush_delayed::he2542202d1def2d9
  17:     0x7fc78d902011 - <rustc_errors::HandlerInner as core::ops::drop::Drop>::drop::h024d44c0c68aef34
  18:     0x7fc78a932196 - core::ptr::drop_in_place::he2f10e88cd1e7c3b
  19:     0x7fc78a935d46 - <alloc::rc::Rc<T> as core::ops::drop::Drop>::drop::hffa852c3f111defc
  20:     0x7fc78a912a1d - core::ptr::drop_in_place::h772d28eb02df6d6d
  21:     0x7fc78a90481d - rustc_span::with_source_map::h3820d41b3a036910
  22:     0x7fc78a93e9c2 - rustc_interface::interface::create_compiler_and_run::h08ad396f4e7721e0
  23:     0x7fc78a926d5a - scoped_tls::ScopedKey<T>::set::hd425a36fbe06985e
  24:     0x7fc78a9439b5 - std::sys_common::backtrace::__rust_begin_short_backtrace::h23925571219dbc63
  25:     0x7fc78a8c13ce - core::ops::function::FnOnce::call_once{{vtable.shim}}::h43b61b9af30b3669
  26:     0x7fc78a06921a - <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once::h88864ee659ddb161
                               at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/alloc/src/boxed.rs:1042:9
  27:     0x7fc78a06921a - <alloc::boxed::Box<F> as core::ops::function::FnOnce<A>>::call_once::h9f03cbdc7ab33431
                               at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/alloc/src/boxed.rs:1042:9
  28:     0x7fc78a06921a - std::sys::unix::thread::Thread::new::thread_start::h5979dd5560a11418
                               at /rustc/ffa2e7ae8fbf9badc035740db949b9dae271c29f/library/std/src/sys/unix/thread.rs:89:17
  29:     0x7fc789f863e9 - start_thread
  30:     0x7fc789ea3293 - __GI___clone
  31:                0x0 - <unknown>

error: internal compiler error: unexpected panic

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 1.49.0-nightly (ffa2e7ae8 2020-10-24) running on x86_64-unknown-linux-gnu

note: compiler flags: -C embed-bitcode=no -C debuginfo=2 -C incremental

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

query stack during panic:
end of query stack
thread panicked while panicking. aborting.
error: could not compile `icedemo`

Caused by:
  process didn't exit successfully: `rustc --crate-name icedemo --edition=2018 src/lib.rs --error-format=json --json=diagnostic-rendered-ansi --emit=dep-info,link -C embed-bitcode=no -C debuginfo=2 --test -C metadata=7ccb3572c942ab87 -C extra-filename=-7ccb3572c942ab87 --out-dir /home/isaac/go/src/github.ibm.com/ifleonar/bitnn/ice_demo/target/debug/deps -C incremental=/home/isaac/go/src/github.ibm.com/ifleonar/bitnn/ice_demo/target/debug/incremental -L dependency=/home/isaac/go/src/github.ibm.com/ifleonar/bitnn/ice_demo/target/debug/deps` (signal: 4, SIGILL: illegal instruction)

[SNCPlay42]

This code compiles on 1.43 (on stable with #![feature(test)] and extern crate test; removed) and ICEs on every later version, but the ICE on 1.46 and before is different.

@rustbot modify labels: regression-from-stable-to-stable

[camelid]

This still produces an ICE (removed the use of the test crate):

pub trait Corge<T> {
    type Fred;
}

impl Corge<u8> for () {
    type Fred = u32;
}

pub trait Waldo {
    type Quax;
}

impl Waldo for u32 {
    type Quax = u8;
}

pub trait Grault
where
    (): Corge<Self::Thud>,
{
    type Thud;
    fn bar(_: <() as Corge<Self::Thud>>::Fred) {}
}

impl<T> Grault for T
where
    T: Waldo,
    (): Corge<T::Quax>,
    <() as Corge<T::Quax>>::Fred: Waldo,
{
    type Thud = u8;
}

pub trait Plugh<I> {
    fn baz();
}

#[derive(Copy, Clone, Debug)]
pub struct Qiz<T> {
    foo: T,
}

impl<T> Plugh<<() as Corge<T::Thud>>::Fred> for Qiz<T>
where
    T: Grault,
    (): Corge<T::Thud>,
{
    fn baz() {}
}

#[cfg(test)]
mod tests {
    use super::{Grault, Plugh, Qiz};

    #[test]
    fn test1() {
        <u32 as Grault>::bar(0u32);
    }

    #[test]
    fn test2() {
        <Qiz<u32> as Plugh<u32>>::baz();
    }
}

[camelid]

(signal: 4, SIGILL: illegal instruction)

This part seems weird. Is that normal for an ICE?

[SNCPlay42]

This also ICEs with mod tests replaced with a pub fn, or fn main in an executable crate, containing the body of test2, e.g.

// traits and impls as before

pub fn test2() {
    <Qiz<u32> as Plugh<u32>>::baz();
}

Or maybe not? I could repro it that way on godbolt but not locally or on playground

Looks like putting it in a pub fn in a lib crate repros it but putting it in main in an executable crate doesn't unless rustc is passed both rlib and bin crate types, which is what I effectively did on godbolt.

[camelid]

searched toolchains nightly-2020-01-01 through nightly-2020-11-01

********************************************************************************
Regression in nightly-2020-04-10
********************************************************************************

Too long ago to get CI builds for individual commits, but the range where the bug was introduced is 485c5fb...94d3463.

[SNCPlay42]

(signal: 4, SIGILL: illegal instruction)

This part seems weird. Is that normal for an ICE?

It's a weird ICE all around. The compiler panics on a failed unwrap, then while unwinding panics again because of a delay_span_bug, so the panic handler calls intrinsics::abort due to panicking while panicking.

It looks like the SIGILL is how intrinsics::abort is implemented.

On 1.46 and before only the second error happened (apparently directly thrown instead of delayed).

[jyn514]

Might have been caused by #70868 ?

[jyn514]

Ah wait no this is in trait_selection, before it gets to codegen.

[jyn514]

Could be #70860, though.

[camelid]

Hard to know because of this ;)