ICE: Error in drop elaboration not found by dropck.

[matthiaskrgr]

auto-reduced (treereduce-rust):

mod defining_scope {
    use super::*;
    pub type Alias<T> = impl Sized;

    pub fn cast<T>(x: Container<Alias<T>, T>) -> Container<T, T> {
        x
    }
}

struct Container<T: Trait<U>, U> {
    x: <T as Trait<U>>::Assoc,
}

trait Trait<T> {
    type Assoc;
}

impl<T> Trait<T> for T {
    type Assoc = Box<u32>;
}
impl<T> Trait<T> for defining_scope::Alias<T> {
    type Assoc = usize;
}

fn main() {
    let x: Box<u32> = defining_scope::cast::<()>(Container { x: 0 }).x;
}

original:

//@ revisions: current next
//@ ignore-compare-mode-next-solver (explicit revisions)
//@[next] compile-flags: -Znext-solver

// A regression test for #105787
#![feature(type_alias_impl_trait)]
mod defining_scope {
    use super::*;
    pub type Alias<T> = impl Sized;

    pub fn cast<T>(x: Container<Alias<T>, T>) -> Container<T, T> {
        //[next]~^ ERROR type annotations needed
        x
    }
}

struct Container<T: Trait<U>, U> {
    x: <T as Trait<U>>::Assoc,
}

trait Trait<T> {
    type Assoc;
}

impl<T> Trait<T> for T {
    type Assoc = Box<u32>;
}
impl<T> Trait<T> for defining_scope::Alias<T> {

    type Assoc = usize;
}

fn main() {
    let x: Box<u32> = defining_scope::cast::<()>(Container { x: 0 }).x;
    println!("{}", *x);
}

Version information

rustc 1.87.0-nightly (ed49386d3 2025-02-19)
binary: rustc
commit-hash: ed49386d3aa3a445a9889707fd405df01723eced
commit-date: 2025-02-19
host: x86_64-unknown-linux-gnu
release: 1.87.0-nightly
LLVM version: 20.1.0

Possibly related line of code:

rust/compiler/rustc_mir_transform/src/elaborate_drop.rs

Lines 275 to 287 in ed49386

	Ok(t) => t,
	Err(_) => Ty::new_error(
	self.tcx(),
	self.elaborator
	.body()
	.tainted_by_errors
	.expect("Error in drop elaboration not found by dropck."),
	),
	};
	(tcx.mk_place_field(base_place, field, field_ty), subpath)
	})
	.collect()

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc

Program output

error[E0658]: `impl Trait` in type aliases is unstable
 --> /tmp/icemaker_global_tempdir.xxzOQICcxqct/rustc_testrunner_tmpdir_reporting.zRTjmeRI0T4S/mvce.rs:3:25
  |
3 |     pub type Alias<T> = impl Sized;
  |                         ^^^^^^^^^^
  |
  = note: see issue #63063 <https://github.com/rust-lang/rust/issues/63063> for more information
  = help: add `#![feature(type_alias_impl_trait)]` to the crate attributes to enable
  = note: this compiler was built on 2025-02-19; consider upgrading it if it is out of date

error[E0119]: conflicting implementations of trait `Trait<_>`
  --> /tmp/icemaker_global_tempdir.xxzOQICcxqct/rustc_testrunner_tmpdir_reporting.zRTjmeRI0T4S/mvce.rs:21:1
   |
18 | impl<T> Trait<T> for T {
   | ---------------------- first implementation here
...
21 | impl<T> Trait<T> for defining_scope::Alias<T> {
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation

warning: unused variable: `x`
  --> /tmp/icemaker_global_tempdir.xxzOQICcxqct/rustc_testrunner_tmpdir_reporting.zRTjmeRI0T4S/mvce.rs:26:9
   |
26 |     let x: Box<u32> = defining_scope::cast::<()>(Container { x: 0 }).x;
   |         ^ help: if this is intentional, prefix it with an underscore: `_x`
   |
   = note: `#[warn(unused_variables)]` on by default


thread 'rustc' panicked at compiler/rustc_mir_transform/src/elaborate_drop.rs:281:30:
Error in drop elaboration not found by dropck.
stack backtrace:
   0:     0x78aff5d9a8e4 - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::h8474fc63c522d8ef
   1:     0x78aff661a2ac - core::fmt::write::h807495cdc673c9ad
   2:     0x78aff758d291 - std::io::Write::write_fmt::ha095d9f81ce0ab0f
   3:     0x78aff5d9a742 - std::sys::backtrace::BacktraceLock::print::h6697e7571ddb1a7a
   4:     0x78aff5d9cf4e - std::panicking::default_hook::{{closure}}::h809b6cc791b58376
   5:     0x78aff5d9cb24 - std::panicking::default_hook::h552e31dd2ff71c94
   6:     0x78aff4ee8d17 - std[751aac3a1d4a21ec]::panicking::update_hook::<alloc[e70108a9cb6abf43]::boxed::Box<rustc_driver_impl[2db46e11a3788224]::install_ice_hook::{closure#1}>>::{closure#0}
   7:     0x78aff5d9d7c3 - std::panicking::rust_panic_with_hook::h31b9a9fc06967d1a
   8:     0x78aff5d9d4ba - std::panicking::begin_panic_handler::{{closure}}::he085f2b5958febbd
   9:     0x78aff5d9ada9 - std::sys::backtrace::__rust_end_short_backtrace::h3acec7353f287c7e
  10:     0x78aff5d9d17d - rust_begin_unwind
  11:     0x78aff2a47050 - core::panicking::panic_fmt::h088f650de8922fae
  12:     0x78aff3d2b39b - core::option::expect_failed::hf1aea988650b4371
  13:     0x78aff7128eb8 - <rustc_mir_transform[5f9d0e5befb1dd62]::elaborate_drop::DropCtxt<rustc_mir_transform[5f9d0e5befb1dd62]::elaborate_drops::ElaborateDropsCtxt>>::elaborate_drop
  14:     0x78aff2ffbea8 - <rustc_mir_transform[5f9d0e5befb1dd62]::elaborate_drops::ElaborateDrops as rustc_mir_transform[5f9d0e5befb1dd62]::pass_manager::MirPass>::run_pass
  15:     0x78aff660979b - rustc_mir_transform[5f9d0e5befb1dd62]::run_analysis_to_runtime_passes
  16:     0x78aff69cf2d9 - rustc_mir_transform[5f9d0e5befb1dd62]::mir_drops_elaborated_and_const_checked
  17:     0x78aff69cef1f - rustc_query_impl[db8619f7f72bce84]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[db8619f7f72bce84]::query_impl::mir_drops_elaborated_and_const_checked::dynamic_query::{closure#2}::{closure#0}, rustc_middle[cad254c74eefe1b7]::query::erase::Erased<[u8; 8usize]>>
  18:     0x78aff69c42cc - rustc_query_system[61afea02fdc7dc5c]::query::plumbing::try_execute_query::<rustc_query_impl[db8619f7f72bce84]::DynamicConfig<rustc_data_structures[7f723801f239d808]::vec_cache::VecCache<rustc_span[3242d24a3aa68a91]::def_id::LocalDefId, rustc_middle[cad254c74eefe1b7]::query::erase::Erased<[u8; 8usize]>, rustc_query_system[61afea02fdc7dc5c]::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl[db8619f7f72bce84]::plumbing::QueryCtxt, false>
  19:     0x78aff69c3d0c - rustc_query_impl[db8619f7f72bce84]::query_impl::mir_drops_elaborated_and_const_checked::get_query_non_incr::__rust_end_short_backtrace
  20:     0x78aff69cc3e2 - rustc_interface[8d7befe99ce7adde]::passes::run_required_analyses
  21:     0x78aff758923a - rustc_interface[8d7befe99ce7adde]::passes::analysis
  22:     0x78aff7589219 - rustc_query_impl[db8619f7f72bce84]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[db8619f7f72bce84]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[cad254c74eefe1b7]::query::erase::Erased<[u8; 0usize]>>
  23:     0x78aff7616883 - rustc_query_system[61afea02fdc7dc5c]::query::plumbing::try_execute_query::<rustc_query_impl[db8619f7f72bce84]::DynamicConfig<rustc_query_system[61afea02fdc7dc5c]::query::caches::SingleCache<rustc_middle[cad254c74eefe1b7]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[db8619f7f72bce84]::plumbing::QueryCtxt, false>
  24:     0x78aff7616553 - rustc_query_impl[db8619f7f72bce84]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  25:     0x78aff7648f3c - rustc_interface[8d7befe99ce7adde]::passes::create_and_enter_global_ctxt::<core[5038f2ec8886dbab]::option::Option<rustc_interface[8d7befe99ce7adde]::queries::Linker>, rustc_driver_impl[2db46e11a3788224]::run_compiler::{closure#0}::{closure#2}>::{closure#2}::{closure#0}
  26:     0x78aff763c8ab - rustc_interface[8d7befe99ce7adde]::interface::run_compiler::<(), rustc_driver_impl[2db46e11a3788224]::run_compiler::{closure#0}>::{closure#1}
  27:     0x78aff7502dc8 - std[751aac3a1d4a21ec]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[8d7befe99ce7adde]::util::run_in_thread_with_globals<rustc_interface[8d7befe99ce7adde]::util::run_in_thread_pool_with_globals<rustc_interface[8d7befe99ce7adde]::interface::run_compiler<(), rustc_driver_impl[2db46e11a3788224]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  28:     0x78aff75031f4 - <<std[751aac3a1d4a21ec]::thread::Builder>::spawn_unchecked_<rustc_interface[8d7befe99ce7adde]::util::run_in_thread_with_globals<rustc_interface[8d7befe99ce7adde]::util::run_in_thread_pool_with_globals<rustc_interface[8d7befe99ce7adde]::interface::run_compiler<(), rustc_driver_impl[2db46e11a3788224]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[5038f2ec8886dbab]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  29:     0x78aff7503baf - std::sys::pal::unix::thread::Thread::new::thread_start::ha52e702df20ec6b5
  30:     0x78aff16a370a - <unknown>
  31:     0x78aff1727aac - <unknown>
  32:                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: rustc 1.87.0-nightly (ed49386d3 2025-02-19) running on x86_64-unknown-linux-gnu

query stack during panic:
#0 [mir_drops_elaborated_and_const_checked] elaborating drops for `main`
#1 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to 2 previous errors; 1 warning emitted

Some errors have detailed explanations: E0119, E0658.
For more information about an error, try `rustc --explain E0119`.

@rustbot label +F-type_alias_impl_trait

[compiler-errors]

cc @matthewjasper