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

[matthiaskrgr]

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:

rust/compiler/rustc_middle/src/ty/normalize_erasing_regions.rs

Lines 165 to 177 in 5c54aa7

	fn normalize_generic_arg_after_erasing_regions(
	&self,
	arg: ty::GenericArg<'tcx>,
	) -> ty::GenericArg<'tcx> {
	let arg = self.typing_env.as_query_input(arg);
	self.tcx.try_normalize_generic_arg_after_erasing_regions(arg).unwrap_or_else(|_| {
	bug!(
	"Failed to normalize {:?} in typing_env={:?}, \
	maybe try to call `try_normalize_erasing_regions` instead",
	arg.value,
	self.typing_env,
	)
	})

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`.

[matthiaskrgr]

bisects to #134798

[matthiaskrgr]

smaller

use std::future::Future;
async fn a() -> impl Sized {
    b(c)
}
async fn c(); // kaboom
fn b<d>(e: d) -> impl Sized
where
    d: f,
{
    || -> <d>::h { panic!() }
}
trait f {
    type h;
}
impl<d, g> f for d
where
    d: Fn() -> g,
    g: Future,
{
}