rust-lang / rust-lang/rust

ICE: `Failed to normalize Alias(Opaque, AliasTy ..`

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-Zvalidate-mir C-bug fixed-by-next-solver I-ICE S-bug-has-test S-has-bisection T-compiler
Dominant language
Rust
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Description

auto-reduced (treereduce-rust):

//@compile-flags: -Zvalidate-mir



use std::future::Future;



async fn create_task() -> impl Sized {
    bind(documentation)
}

async fn documentation() {
    !;
    
}

fn bind<F>(_filter: F) -> impl Sized
where
    F: FilterBase,
{
    || -> <F as FilterBase>::Assoc { panic!() }
}

trait FilterBase {
    type Assoc;
}

impl<F, R> FilterBase for F
where
    F: Fn() -> R,
    
    R: Future,
    
    R: Send,
    
{
    
     
     
}

original:

// Regression test for #135668
//@ edition: 2021

use std::future::Future;

pub async fn foo() {
    let _ = create_task().await;
}

async fn create_task() -> impl Sized {
    bind(documentation)
}

async fn documentation() {
    compile_error!("bonjour");
    //~^ ERROR bonjour
}

fn bind<F>(_filter: F) -> impl Sized
where
    F: FilterBase,
{
    || -> <F as FilterBase>::Assoc { panic!() }
}

trait FilterBase {
    type Assoc;
}

impl<F, R> FilterBase for F
where
    F: Fn() -> R,
    // Removing the below line makes it correctly error on both stable and beta
    R: Future,
    // Removing the below line makes it ICE on both stable and beta
    R: Send,
    // Removing the above two bounds makes it ICE on stable but correctly error on beta
{
    type Type = ();
    const CONST: usize = 1; //~ NOTE candidate #2
    fn foo(&self) {} //~ NOTE candidate #2
}

fn main() {}

Version information

rustc 1.88.0-nightly (5c54aa781 2025-04-25)
binary: rustc
commit-hash: 5c54aa781f97ae95ef01a3120650907b87d385d3
commit-date: 2025-04-25
host: x86_64-unknown-linux-gnu
release: 1.88.0-nightly
LLVM version: 20.1.2

Possibly related line of code:
https://github.com/rust-lang/rust/blob/5c54aa781f97ae95ef01a3120650907b87d385d3/compiler/rustc_middle/src/ty/normalize_erasing_regions.rs#L165-L177

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc -Zvalidate-mir

Program output 

error[E0670]: `async fn` is not permitted in Rust 2015
 --> /tmp/icemaker_global_tempdir.Fy7kUrdY3L11/rustc_testrunner_tmpdir_reporting.oROTq4nV8k6c/mvce.rs:8:1
  |
8 | async fn create_task() -> impl Sized {
  | ^^^^^ to use `async fn`, switch to Rust 2018 or later
  |
  = help: pass `--edition 2024` to `rustc`
  = note: for more on editions, read https://doc.rust-lang.org/edition-guide

error[E0670]: `async fn` is not permitted in Rust 2015
  --> /tmp/icemaker_global_tempdir.Fy7kUrdY3L11/rustc_testrunner_tmpdir_reporting.oROTq4nV8k6c/mvce.rs:12:1
   |
12 | async fn documentation() {
   | ^^^^^ to use `async fn`, switch to Rust 2018 or later
   |
   = help: pass `--edition 2024` to `rustc`
   = note: for more on editions, read https://doc.rust-lang.org/edition-guide

error: expected expression, found `;`
  --> /tmp/icemaker_global_tempdir.Fy7kUrdY3L11/rustc_testrunner_tmpdir_reporting.oROTq4nV8k6c/mvce.rs:13:6
   |
13 |     !;
   |      ^ expected expression

error[E0601]: `main` function not found in crate `mvce`
  --> /tmp/icemaker_global_tempdir.Fy7kUrdY3L11/rustc_testrunner_tmpdir_reporting.oROTq4nV8k6c/mvce.rs:40:2
   |
40 | }
   |  ^ consider adding a `main` function to `/tmp/icemaker_global_tempdir.Fy7kUrdY3L11/rustc_testrunner_tmpdir_reporting.oROTq4nV8k6c/mvce.rs`

error[E0046]: not all trait items implemented, missing: `Assoc`
  --> /tmp/icemaker_global_tempdir.Fy7kUrdY3L11/rustc_testrunner_tmpdir_reporting.oROTq4nV8k6c/mvce.rs:28:1
   |
25 |       type Assoc;
   |       ---------- `Assoc` from trait
...
28 | / impl<F, R> FilterBase for F
29 | | where
30 | |     F: Fn() -> R,
...  |
34 | |     R: Send,
   | |____________^ missing `Assoc` in implementation

error: internal compiler error: compiler/rustc_middle/src/ty/normalize_erasing_regions.rs:171:13: Failed to normalize Alias(Opaque, AliasTy { args: [FnDef(DefId(0:8 ~ mvce[1e52]::documentation), [])], def_id: DefId(0:13 ~ mvce[1e52]::bind::{opaque#0}), .. }) in typing_env=TypingEnv { typing_mode: PostAnalysis, param_env: ParamEnv { caller_bounds: [] } }, maybe try to call `try_normalize_erasing_regions` instead


thread 'rustc' panicked at compiler/rustc_middle/src/ty/normalize_erasing_regions.rs:171:13:
Box<dyn Any>
stack backtrace:
   0:     0x7d390ed01a93 - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::h5e5ed7e3dba37109
   1:     0x7d390f405ac7 - core::fmt::write::h9eb703e77e802118
   2:     0x7d39107f2951 - std::io::Write::write_fmt::h86cc522f97972765
   3:     0x7d390ed018f2 - std::sys::backtrace::BacktraceLock::print::h6a10f5f1a1008df7
   4:     0x7d390ed0526a - std::panicking::default_hook::{{closure}}::hc9375e73d24b3054
   5:     0x7d390ed04def - std::panicking::default_hook::hf26154a2d0532fd5
   6:     0x7d390dd75893 - std[ec78c589ec7e8aee]::panicking::update_hook::<alloc[64039d61152c796e]::boxed::Box<rustc_driver_impl[ebb0c86317587fd1]::install_ice_hook::{closure#1}>>::{closure#0}
   7:     0x7d390ed05ae3 - std::panicking::rust_panic_with_hook::h9fb4aeb43df093ef
   8:     0x7d390ddb1271 - std[ec78c589ec7e8aee]::panicking::begin_panic::<rustc_errors[737037f1c0007803]::ExplicitBug>::{closure#0}
   9:     0x7d390dda52a6 - std[ec78c589ec7e8aee]::sys::backtrace::__rust_end_short_backtrace::<std[ec78c589ec7e8aee]::panicking::begin_panic<rustc_errors[737037f1c0007803]::ExplicitBug>::{closure#0}, !>
  10:     0x7d390dda5137 - std[ec78c589ec7e8aee]::panicking::begin_panic::<rustc_errors[737037f1c0007803]::ExplicitBug>
  11:     0x7d390ddbb641 - <rustc_errors[737037f1c0007803]::diagnostic::BugAbort as rustc_errors[737037f1c0007803]::diagnostic::EmissionGuarantee>::emit_producing_guarantee
  12:     0x7d390e4045ea - rustc_middle[e11bc8960ffe44ac]::util::bug::opt_span_bug_fmt::<rustc_span[10bfa2f3d1cd0e94]::span_encoding::Span>::{closure#0}
  13:     0x7d390e3df60a - rustc_middle[e11bc8960ffe44ac]::ty::context::tls::with_opt::<rustc_middle[e11bc8960ffe44ac]::util::bug::opt_span_bug_fmt<rustc_span[10bfa2f3d1cd0e94]::span_encoding::Span>::{closure#0}, !>::{closure#0}
  14:     0x7d390e3df47b - rustc_middle[e11bc8960ffe44ac]::ty::context::tls::with_context_opt::<rustc_middle[e11bc8960ffe44ac]::ty::context::tls::with_opt<rustc_middle[e11bc8960ffe44ac]::util::bug::opt_span_bug_fmt<rustc_span[10bfa2f3d1cd0e94]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  15:     0x7d390b68dda0 - rustc_middle[e11bc8960ffe44ac]::util::bug::bug_fmt
  16:     0x7d390fd99084 - <rustc_middle[e11bc8960ffe44ac]::ty::normalize_erasing_regions::NormalizeAfterErasingRegionsFolder as rustc_type_ir[e02aabdd9006fd47]::fold::TypeFolder<rustc_middle[e11bc8960ffe44ac]::ty::context::TyCtxt>>::fold_ty
  17:     0x7d39106f3fb5 - rustc_mir_transform[8d2ddc6cd67b9b7]::validate::validate_types
  18:     0x7d39104fe241 - <rustc_mir_transform[8d2ddc6cd67b9b7]::validate::Validator as rustc_mir_transform[8d2ddc6cd67b9b7]::pass_manager::MirPass>::run_pass
  19:     0x7d390d5bbb85 - rustc_mir_transform[8d2ddc6cd67b9b7]::pass_manager::validate_body
  20:     0x7d390f40d1cd - rustc_mir_transform[8d2ddc6cd67b9b7]::run_analysis_to_runtime_passes
  21:     0x7d390f96f9e5 - rustc_mir_transform[8d2ddc6cd67b9b7]::mir_drops_elaborated_and_const_checked
  22:     0x7d390f96f399 - rustc_query_impl[54ec0e3327109f1d]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[54ec0e3327109f1d]::query_impl::mir_drops_elaborated_and_const_checked::dynamic_query::{closure#2}::{closure#0}, rustc_middle[e11bc8960ffe44ac]::query::erase::Erased<[u8; 8usize]>>
  23:     0x7d390f7622ac - rustc_query_system[1188370fe5183a9d]::query::plumbing::try_execute_query::<rustc_query_impl[54ec0e3327109f1d]::DynamicConfig<rustc_data_structures[d8d4b55b44c07e9d]::vec_cache::VecCache<rustc_span[10bfa2f3d1cd0e94]::def_id::LocalDefId, rustc_middle[e11bc8960ffe44ac]::query::erase::Erased<[u8; 8usize]>, rustc_query_system[1188370fe5183a9d]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[54ec0e3327109f1d]::plumbing::QueryCtxt, false>
  24:     0x7d390f761b8f - rustc_query_impl[54ec0e3327109f1d]::query_impl::mir_drops_elaborated_and_const_checked::get_query_non_incr::__rust_end_short_backtrace
  25:     0x7d390fe40e18 - rustc_interface[394fb8669b43967f]::passes::run_required_analyses
  26:     0x7d39102d1a9e - rustc_interface[394fb8669b43967f]::passes::analysis
  27:     0x7d39102d1a6d - rustc_query_impl[54ec0e3327109f1d]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[54ec0e3327109f1d]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[e11bc8960ffe44ac]::query::erase::Erased<[u8; 0usize]>>
  28:     0x7d39102d753d - rustc_query_system[1188370fe5183a9d]::query::plumbing::try_execute_query::<rustc_query_impl[54ec0e3327109f1d]::DynamicConfig<rustc_query_system[1188370fe5183a9d]::query::caches::SingleCache<rustc_middle[e11bc8960ffe44ac]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[54ec0e3327109f1d]::plumbing::QueryCtxt, false>
  29:     0x7d39102d7238 - rustc_query_impl[54ec0e3327109f1d]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  30:     0x7d3910651e80 - rustc_interface[394fb8669b43967f]::passes::create_and_enter_global_ctxt::<core[db792b049954ae76]::option::Option<rustc_interface[394fb8669b43967f]::queries::Linker>, rustc_driver_impl[ebb0c86317587fd1]::run_compiler::{closure#0}::{closure#2}>::{closure#2}::{closure#0}
  31:     0x7d39104e9084 - rustc_interface[394fb8669b43967f]::interface::run_compiler::<(), rustc_driver_impl[ebb0c86317587fd1]::run_compiler::{closure#0}>::{closure#1}
  32:     0x7d39104a3234 - std[ec78c589ec7e8aee]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[394fb8669b43967f]::util::run_in_thread_with_globals<rustc_interface[394fb8669b43967f]::util::run_in_thread_pool_with_globals<rustc_interface[394fb8669b43967f]::interface::run_compiler<(), rustc_driver_impl[ebb0c86317587fd1]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  33:     0x7d39104a3674 - <<std[ec78c589ec7e8aee]::thread::Builder>::spawn_unchecked_<rustc_interface[394fb8669b43967f]::util::run_in_thread_with_globals<rustc_interface[394fb8669b43967f]::util::run_in_thread_pool_with_globals<rustc_interface[394fb8669b43967f]::interface::run_compiler<(), rustc_driver_impl[ebb0c86317587fd1]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[db792b049954ae76]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  34:     0x7d39104a4a6b - std::sys::pal::unix::thread::Thread::new::thread_start::hd4f8a3dac6df8331
  35:     0x7d390a2a370a - <unknown>
  36:     0x7d390a327aac - <unknown>
  37:                0x0 - <unknown>

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: rustc 1.88.0-nightly (5c54aa781 2025-04-25) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z validate-mir -Z dump-mir-dir=dir

query stack during panic:
#0 [mir_drops_elaborated_and_const_checked] elaborating drops for `create_task::{closure#0}`
#1 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to 6 previous errors

Some errors have detailed explanations: E0046, E0601, E0670.
For more information about an error, try `rustc --explain E0046`.

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by reproducing the reduced a.rs case with rustc -Zvalidate-mir, then inspect compiler/rustc_middle/src/ty/normalize_erasing_regions.rs around lines 165-177 and the MIR validation path shown in the backtrace. Done means this input no longer triggers an internal compiler error and produces the intended diagnostics, with coverage for the regression case.

Written by the indexing model from the issue text.

Assessment

Tech stack
rust
Domain
compilers
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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