rust-lang / rust-lang/rust

ICE with `feature(non_lifetime_binders)` for trait generic that is constrained equal to supertrait associated type.

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C-bug F-non_lifetime_binders I-ICE S-bug-has-test T-compiler T-types
Dominant language
Rust
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Description

Code
#![feature(non_lifetime_binders)]
#![allow(unused)]

trait A<T>: Iterator<Item = T> {}

fn demo(x: &mut impl for<U> A<U>) {
    let _: Option<u32> = x.next(); // Removing this line stops the ICE
}
Meta

rustc --version --verbose:

rustc 1.83.0-nightly (0609062a9 2024-09-13)
binary: rustc
commit-hash: 0609062a91c8f445c3e9a0de57e402f9b1b8b0a7
commit-date: 2024-09-13
host: x86_64-unknown-linux-gnu
release: 1.83.0-nightly
LLVM version: 19.1.0
Error output
thread 'rustc' panicked at compiler/rustc_borrowck/src/type_check/relate_tys.rs:343:9:
unexpected inference var std::option::Option<?0t>
Backtrace 

$ RUST_BACKTRACE=full cargo build 
   Compiling non-lifetime-binders-ice v0.1.0 (/home/zachary/Programming/rusttesting/non-lifetime-binders-ice)
warning: the feature `non_lifetime_binders` is incomplete and may not be safe to use and/or cause compiler crashes
 --> src/lib.rs:1:12
  |
1 | #![feature(non_lifetime_binders)]
  |            ^^^^^^^^^^^^^^^^^^^^
  |
  = note: see issue #108185 <https://github.com/rust-lang/rust/issues/108185> for more information
  = note: `#[warn(incomplete_features)]` on by default

thread 'rustc' panicked at compiler/rustc_borrowck/src/type_check/relate_tys.rs:343:9:
unexpected inference var std::option::Option<?0t>
stack backtrace:
   0:     0x7df233a7701a - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::h85a9257eb6c41e04
   1:     0x7df234203257 - core::fmt::write::hcc8bee8d21353e39
   2:     0x7df23515c4b3 - std::io::Write::write_fmt::h70ac935b0c89b059
   3:     0x7df233a76e72 - std::sys::backtrace::BacktraceLock::print::hd262bc6f83870824
   4:     0x7df233a795f1 - std::panicking::default_hook::{{closure}}::h1ac01a4d50ceb64f
   5:     0x7df233a79424 - std::panicking::default_hook::h7c4ba54603c1d0b3
   6:     0x7df232b7ccff - std[b495ad0c4617e146]::panicking::update_hook::<alloc[a0425571c9a9acf]::boxed::Box<rustc_driver_impl[f22662736fcaf763]::install_ice_hook::{closure#0}>>::{closure#0}
   7:     0x7df233a79d18 - std::panicking::rust_panic_with_hook::h0dd05eda4407feb9
   8:     0x7df233a79ae7 - std::panicking::begin_panic_handler::{{closure}}::hff4951198a9049be
   9:     0x7df233a774c9 - std::sys::backtrace::__rust_end_short_backtrace::hae232f20e82e2c44
  10:     0x7df233a797b4 - rust_begin_unwind
  11:     0x7df230894523 - core::panicking::panic_fmt::h6dddd3310fdcb8b7
  12:     0x7df23443ca7f - <rustc_borrowck[a2299cf35e33e6d2]::type_check::relate_tys::NllTypeRelating as rustc_type_ir[a35413f6f42f08]::relate::TypeRelation<rustc_middle[7cca7f2870ea52e7]::ty::context::TyCtxt>>::tys
  13:     0x7df234447572 - <rustc_borrowck[a2299cf35e33e6d2]::type_check::TypeChecker>::typeck_mir
  14:     0x7df235302842 - rustc_borrowck[a2299cf35e33e6d2]::type_check::type_check
  15:     0x7df2342c4549 - rustc_borrowck[a2299cf35e33e6d2]::nll::compute_regions
  16:     0x7df2352b18c8 - rustc_borrowck[a2299cf35e33e6d2]::do_mir_borrowck
  17:     0x7df2352a3f87 - rustc_query_impl[484dcaccf014b2f3]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[484dcaccf014b2f3]::query_impl::mir_borrowck::dynamic_query::{closure#2}::{closure#0}, rustc_middle[7cca7f2870ea52e7]::query::erase::Erased<[u8; 8usize]>>
  18:     0x7df2344925d4 - rustc_query_system[a8532041af820499]::query::plumbing::try_execute_query::<rustc_query_impl[484dcaccf014b2f3]::DynamicConfig<rustc_query_system[a8532041af820499]::query::caches::VecCache<rustc_span[45f656ad9ccc3ab8]::def_id::LocalDefId, rustc_middle[7cca7f2870ea52e7]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[484dcaccf014b2f3]::plumbing::QueryCtxt, true>
  19:     0x7df234497434 - rustc_query_impl[484dcaccf014b2f3]::query_impl::mir_borrowck::get_query_incr::__rust_end_short_backtrace
  20:     0x7df234a7e278 - rustc_interface[1ce9087adc29d20e]::passes::run_required_analyses
  21:     0x7df2350b4b9e - rustc_interface[1ce9087adc29d20e]::passes::analysis
  22:     0x7df2350b4b71 - rustc_query_impl[484dcaccf014b2f3]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[484dcaccf014b2f3]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[7cca7f2870ea52e7]::query::erase::Erased<[u8; 1usize]>>
  23:     0x7df2350bdc4d - rustc_query_system[a8532041af820499]::query::plumbing::try_execute_query::<rustc_query_impl[484dcaccf014b2f3]::DynamicConfig<rustc_query_system[a8532041af820499]::query::caches::SingleCache<rustc_middle[7cca7f2870ea52e7]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[484dcaccf014b2f3]::plumbing::QueryCtxt, true>
  24:     0x7df2350bd8fa - rustc_query_impl[484dcaccf014b2f3]::query_impl::analysis::get_query_incr::__rust_end_short_backtrace
  25:     0x7df234f3aafc - rustc_interface[1ce9087adc29d20e]::interface::run_compiler::<core[7f44e8b513577cf8]::result::Result<(), rustc_span[45f656ad9ccc3ab8]::ErrorGuaranteed>, rustc_driver_impl[f22662736fcaf763]::run_compiler::{closure#0}>::{closure#1}
  26:     0x7df23503fc50 - std[b495ad0c4617e146]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[1ce9087adc29d20e]::util::run_in_thread_with_globals<rustc_interface[1ce9087adc29d20e]::util::run_in_thread_pool_with_globals<rustc_interface[1ce9087adc29d20e]::interface::run_compiler<core[7f44e8b513577cf8]::result::Result<(), rustc_span[45f656ad9ccc3ab8]::ErrorGuaranteed>, rustc_driver_impl[f22662736fcaf763]::run_compiler::{closure#0}>::{closure#1}, core[7f44e8b513577cf8]::result::Result<(), rustc_span[45f656ad9ccc3ab8]::ErrorGuaranteed>>::{closure#0}, core[7f44e8b513577cf8]::result::Result<(), rustc_span[45f656ad9ccc3ab8]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[7f44e8b513577cf8]::result::Result<(), rustc_span[45f656ad9ccc3ab8]::ErrorGuaranteed>>
  27:     0x7df2350402ba - <<std[b495ad0c4617e146]::thread::Builder>::spawn_unchecked_<rustc_interface[1ce9087adc29d20e]::util::run_in_thread_with_globals<rustc_interface[1ce9087adc29d20e]::util::run_in_thread_pool_with_globals<rustc_interface[1ce9087adc29d20e]::interface::run_compiler<core[7f44e8b513577cf8]::result::Result<(), rustc_span[45f656ad9ccc3ab8]::ErrorGuaranteed>, rustc_driver_impl[f22662736fcaf763]::run_compiler::{closure#0}>::{closure#1}, core[7f44e8b513577cf8]::result::Result<(), rustc_span[45f656ad9ccc3ab8]::ErrorGuaranteed>>::{closure#0}, core[7f44e8b513577cf8]::result::Result<(), rustc_span[45f656ad9ccc3ab8]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[7f44e8b513577cf8]::result::Result<(), rustc_span[45f656ad9ccc3ab8]::ErrorGuaranteed>>::{closure#1} as core[7f44e8b513577cf8]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  28:     0x7df2350406ab - std::sys::pal::unix::thread::Thread::new::thread_start::hdd18e2f9323a466b
  29:     0x7df22f29ca94 - start_thread
                               at ./nptl/pthread_create.c:447:8
  30:     0x7df22f329c3c - clone3
                               at ./misc/../sysdeps/unix/sysv/linux/x86_64/clone3.S:78
  31:                0x0 - <unknown>

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: please make sure that you have updated to the latest nightly

note: please attach the file at `/home/zachary/Programming/rusttesting/non-lifetime-binders-ice/rustc-ice-2024-09-14T08_33_54-96527.txt` to your bug report

note: compiler flags: --crate-type lib -C embed-bitcode=no -C debuginfo=2 -C incremental=[REDACTED]

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

query stack during panic:
#0 [mir_borrowck] borrow-checking `demo`
#1 [analysis] running analysis passes on this crate
end of query stack
warning: `non-lifetime-binders-ice` (lib) generated 1 warning
error: could not compile `non-lifetime-binders-ice` (lib); 1 warning emitted

Caused by:
  process didn't exit successfully: `/home/zachary/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/rustc --crate-name non_lifetime_binders_ice --edition=2021 src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --diagnostic-width=180 --crate-type lib --emit=dep-info,metadata,link -C embed-bitcode=no -C debuginfo=2 --check-cfg 'cfg(docsrs)' --check-cfg 'cfg(feature, values())' -C metadata=f19fe47f3fdd4a9f -C extra-filename=-f19fe47f3fdd4a9f --out-dir /home/zachary/opt_mount/zachary/cargo-target/debug/deps -C incremental=/home/zachary/opt_mount/zachary/cargo-target/debug/incremental -L dependency=/home/zachary/opt_mount/zachary/cargo-target/debug/deps` (exit status: 101)

/.../non-lifetime-binders-ice/rustc-ice-2024-09-14T08_33_54-96527.txt:

thread 'rustc' panicked at compiler/rustc_borrowck/src/type_check/relate_tys.rs:343:9:
unexpected inference var std::option::Option<?0t>
stack backtrace:
   0:     0x7df23543dbe5 - std::backtrace::Backtrace::create::h47c5ac21bc5295ff
   1:     0x7df233a62695 - std::backtrace::Backtrace::force_capture::h22d7360fb10c606e
   2:     0x7df232b7d337 - std[b495ad0c4617e146]::panicking::update_hook::<alloc[a0425571c9a9acf]::boxed::Box<rustc_driver_impl[f22662736fcaf763]::install_ice_hook::{closure#0}>>::{closure#0}
   3:     0x7df233a79d18 - std::panicking::rust_panic_with_hook::h0dd05eda4407feb9
   4:     0x7df233a79ae7 - std::panicking::begin_panic_handler::{{closure}}::hff4951198a9049be
   5:     0x7df233a774c9 - std::sys::backtrace::__rust_end_short_backtrace::hae232f20e82e2c44
   6:     0x7df233a797b4 - rust_begin_unwind
   7:     0x7df230894523 - core::panicking::panic_fmt::h6dddd3310fdcb8b7
   8:     0x7df23443ca7f - <rustc_borrowck[a2299cf35e33e6d2]::type_check::relate_tys::NllTypeRelating as rustc_type_ir[a35413f6f42f08]::relate::TypeRelation<rustc_middle[7cca7f2870ea52e7]::ty::context::TyCtxt>>::tys
   9:     0x7df234447572 - <rustc_borrowck[a2299cf35e33e6d2]::type_check::TypeChecker>::typeck_mir
  10:     0x7df235302842 - rustc_borrowck[a2299cf35e33e6d2]::type_check::type_check
  11:     0x7df2342c4549 - rustc_borrowck[a2299cf35e33e6d2]::nll::compute_regions
  12:     0x7df2352b18c8 - rustc_borrowck[a2299cf35e33e6d2]::do_mir_borrowck
  13:     0x7df2352a3f87 - rustc_query_impl[484dcaccf014b2f3]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[484dcaccf014b2f3]::query_impl::mir_borrowck::dynamic_query::{closure#2}::{closure#0}, rustc_middle[7cca7f2870ea52e7]::query::erase::Erased<[u8; 8usize]>>
  14:     0x7df2344925d4 - rustc_query_system[a8532041af820499]::query::plumbing::try_execute_query::<rustc_query_impl[484dcaccf014b2f3]::DynamicConfig<rustc_query_system[a8532041af820499]::query::caches::VecCache<rustc_span[45f656ad9ccc3ab8]::def_id::LocalDefId, rustc_middle[7cca7f2870ea52e7]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[484dcaccf014b2f3]::plumbing::QueryCtxt, true>
  15:     0x7df234497434 - rustc_query_impl[484dcaccf014b2f3]::query_impl::mir_borrowck::get_query_incr::__rust_end_short_backtrace
  16:     0x7df234a7e278 - rustc_interface[1ce9087adc29d20e]::passes::run_required_analyses
  17:     0x7df2350b4b9e - rustc_interface[1ce9087adc29d20e]::passes::analysis
  18:     0x7df2350b4b71 - rustc_query_impl[484dcaccf014b2f3]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[484dcaccf014b2f3]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[7cca7f2870ea52e7]::query::erase::Erased<[u8; 1usize]>>
  19:     0x7df2350bdc4d - rustc_query_system[a8532041af820499]::query::plumbing::try_execute_query::<rustc_query_impl[484dcaccf014b2f3]::DynamicConfig<rustc_query_system[a8532041af820499]::query::caches::SingleCache<rustc_middle[7cca7f2870ea52e7]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[484dcaccf014b2f3]::plumbing::QueryCtxt, true>
  20:     0x7df2350bd8fa - rustc_query_impl[484dcaccf014b2f3]::query_impl::analysis::get_query_incr::__rust_end_short_backtrace
  21:     0x7df234f3aafc - rustc_interface[1ce9087adc29d20e]::interface::run_compiler::<core[7f44e8b513577cf8]::result::Result<(), rustc_span[45f656ad9ccc3ab8]::ErrorGuaranteed>, rustc_driver_impl[f22662736fcaf763]::run_compiler::{closure#0}>::{closure#1}
  22:     0x7df23503fc50 - std[b495ad0c4617e146]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[1ce9087adc29d20e]::util::run_in_thread_with_globals<rustc_interface[1ce9087adc29d20e]::util::run_in_thread_pool_with_globals<rustc_interface[1ce9087adc29d20e]::interface::run_compiler<core[7f44e8b513577cf8]::result::Result<(), rustc_span[45f656ad9ccc3ab8]::ErrorGuaranteed>, rustc_driver_impl[f22662736fcaf763]::run_compiler::{closure#0}>::{closure#1}, core[7f44e8b513577cf8]::result::Result<(), rustc_span[45f656ad9ccc3ab8]::ErrorGuaranteed>>::{closure#0}, core[7f44e8b513577cf8]::result::Result<(), rustc_span[45f656ad9ccc3ab8]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[7f44e8b513577cf8]::result::Result<(), rustc_span[45f656ad9ccc3ab8]::ErrorGuaranteed>>
  23:     0x7df2350402ba - <<std[b495ad0c4617e146]::thread::Builder>::spawn_unchecked_<rustc_interface[1ce9087adc29d20e]::util::run_in_thread_with_globals<rustc_interface[1ce9087adc29d20e]::util::run_in_thread_pool_with_globals<rustc_interface[1ce9087adc29d20e]::interface::run_compiler<core[7f44e8b513577cf8]::result::Result<(), rustc_span[45f656ad9ccc3ab8]::ErrorGuaranteed>, rustc_driver_impl[f22662736fcaf763]::run_compiler::{closure#0}>::{closure#1}, core[7f44e8b513577cf8]::result::Result<(), rustc_span[45f656ad9ccc3ab8]::ErrorGuaranteed>>::{closure#0}, core[7f44e8b513577cf8]::result::Result<(), rustc_span[45f656ad9ccc3ab8]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[7f44e8b513577cf8]::result::Result<(), rustc_span[45f656ad9ccc3ab8]::ErrorGuaranteed>>::{closure#1} as core[7f44e8b513577cf8]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  24:     0x7df2350406ab - std::sys::pal::unix::thread::Thread::new::thread_start::hdd18e2f9323a466b
  25:     0x7df22f29ca94 - start_thread
                               at ./nptl/pthread_create.c:447:8
  26:     0x7df22f329c3c - clone3
                               at ./misc/../sysdeps/unix/sysv/linux/x86_64/clone3.S:78
  27:                0x0 - <unknown>


rustc version: 1.83.0-nightly (0609062a9 2024-09-13)
platform: x86_64-unknown-linux-gnu

query stack during panic:
#0 [mir_borrowck] borrow-checking `demo`
#1 [analysis] running analysis passes on this crate
end of query stack

@rustbot label +F-non-lifetime-binders +requires-nightly

Contributor guide

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First steps

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  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Reproduce the minimal example with the reported nightly compiler, then start at compiler/rustc_borrowck/src/type_check/relate_tys.rs:343 and follow the mir_borrowck query path shown in the backtrace. Determine why this case reaches the unexpected inference variable panic and add coverage so the example no longer causes an internal compiler error.

Written by the indexing model from the issue text.

Assessment

Tech stack
rust
Domain
compilers
Issue type
Bug
Difficulty
5/5
Estimated time
Over a week
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
30/100

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