ICE: broken MIR: NoSolution on HRTB over GAT in trait object

[ecryth]

Code

MWE below, also tested on nightly (via the playground). Interestingly the error goes away if I manually inline the Node::new calls. Minimised from a filter graph that uses trait objects for type erasure.

pub trait Transform {
    type Output<'a>;
}

pub trait Propagate<Input> {}

type Child<T> = Box<dyn for<'a> Propagate<<T as Transform>::Output<'a>>>;

pub struct Node<T>
where
    T: Transform,
{
    transform: T,
    children: Vec<Child<T>>,
}

impl<T> Node<T>
where
    T: Transform,
{
    pub fn new(transform: T, children: Vec<Child<T>>) -> Self {
        Node {
            transform,
            children,
        }
    }
}

impl<Input, T> Propagate<Input> for Node<T> where T: Transform {}

pub fn main() {
    struct Noop;

    impl Transform for Noop {
        type Output<'a> = ();
    }

    let node = Box::new(Node::new(Noop, vec![Box::new(Node::new(Noop, vec![]))]));
}

Meta

rustc --version --verbose:

rustc 1.81.0 (eeb90cda1 2024-09-04)
binary: rustc
commit-hash: eeb90cda1969383f56a2637cbd3037bdf598841c
commit-date: 2024-09-04
host: x86_64-unknown-linux-gnu
release: 1.81.0
LLVM version: 18.1.7

Error output

error: internal compiler error: broken MIR in DefId(0:31 ~ playground[6f8d]::test::run#1) ([move _11]): std::boxed::Box<dyn [Binder { value: Trait(Propagate<()>), bound_vars: [Region(BrNamed(DefId(0:10 ~ playground[6f8d]::Child::'a), 'a))] }] + '?14, std::alloc::Global> is not a subtype of std::boxed::Box<dyn [Binder { value: Trait(Propagate<<test::Noop as Transform>::Output<'a>>), bound_vars: [Region(BrNamed(DefId(0:10 ~ playground[6f8d]::Child::'a), 'a))] }] + '?7, std::alloc::Global>: NoSolution
  --> src/lib.rs:43:45
   |
43 |         let node = Box::new(Node::new(Noop, vec![Box::new(Node::new(Noop, vec![]))]));
   |                                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
note: delayed at compiler/rustc_borrowck/src/type_check/mod.rs:2570:17 - disabled backtrace
  --> src/lib.rs:43:45
   |
43 |         let node = Box::new(Node::new(Noop, vec![Box::new(Node::new(Noop, vec![]))]));
   |                                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   = note: this error: internal compiler error originates in the macro `vec` (in Nightly builds, run with -Z macro-backtrace for more info)

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 1.81.0 (eeb90cda1 2024-09-04) running on x86_64-unknown-linux-gnu

note: compiler flags: -C embed-bitcode=no -C codegen-units=1 -C debuginfo=2

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

query stack during panic:
end of query stack

Backtrace

   Compiling my_test v0.1.0 (/tmp/my_test)
warning: unused variable: `node`
  --> src/main.rs:38:9
   |
38 |     let node = Box::new(Node::new(Noop, vec![Box::new(Node::new(Noop, vec![]))]));
   |         ^^^^ help: if this is intentional, prefix it with an underscore: `_node`
   |
   = note: `#[warn(unused_variables)]` on by default

warning: fields `transform` and `children` are never read
  --> src/main.rs:13:5
   |
9  | pub struct Node<T>
   |            ---- fields in this struct
...
13 |     transform: T,
   |     ^^^^^^^^^
14 |     children: Vec<Child<T>>,
   |     ^^^^^^^^
   |
   = note: `#[warn(dead_code)]` on by default

note: no errors encountered even though delayed bugs were created

note: those delayed bugs will now be shown as internal compiler errors

error: internal compiler error: broken MIR in DefId(0:21 ~ my_test[db07]::main) ([move _11]): std::boxed::Box<dyn [Binder { value: Trait(Propagate<()>), bound_vars: [Region(BrNamed(DefId(0:10 ~ my_test[db07]::Child::'a), 'a))] }] + '?14, std::alloc::Global> is not a subtype of std::boxed::Box<dyn [Binder { value: Trait(Propagate<<main::Noop as Transform>::Output<'a>>), bound_vars: [Region(BrNamed(DefId(0:10 ~ my_test[db07]::Child::'a), 'a))] }] + '?7, std::alloc::Global>: NoSolution
  --> src/main.rs:38:41
   |
38 |     let node = Box::new(Node::new(Noop, vec![Box::new(Node::new(Noop, vec![]))]));
   |                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
note: delayed at compiler/rustc_borrowck/src/type_check/mod.rs:2570:17
         0: <rustc_errors::DiagCtxtInner>::emit_diagnostic
         1: <rustc_errors::DiagCtxtHandle>::emit_diagnostic
         2: <rustc_span::ErrorGuaranteed as rustc_errors::diagnostic::EmissionGuarantee>::emit_producing_guarantee
         3: <rustc_errors::DiagCtxtHandle>::span_delayed_bug::<rustc_span::span_encoding::Span, alloc::string::String>
         4: <rustc_borrowck::type_check::TypeChecker>::typeck_mir
         5: rustc_borrowck::type_check::type_check
         6: rustc_borrowck::nll::compute_regions
         7: rustc_borrowck::do_mir_borrowck
         8: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::mir_borrowck::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 8]>>
         9: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::VecCache<rustc_span::def_id::LocalDefId, rustc_middle::query::erase::Erased<[u8; 8]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, true>
        10: rustc_query_impl::query_impl::mir_borrowck::get_query_incr::__rust_end_short_backtrace
        11: rustc_interface::passes::analysis
        12: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 1]>>
        13: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::SingleCache<rustc_middle::query::erase::Erased<[u8; 1]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, true>
        14: rustc_query_impl::query_impl::analysis::get_query_incr::__rust_end_short_backtrace
        15: rustc_interface::interface::run_compiler::<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}
        16: std::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface::util::run_in_thread_with_globals<rustc_interface::interface::run_compiler<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{closure#0}::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>
        17: <<std::thread::Builder>::spawn_unchecked_<rustc_interface::util::run_in_thread_with_globals<rustc_interface::interface::run_compiler<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{closure#0}::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{closure#1} as core::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
        18: <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once
                   at /rustc/eeb90cda1969383f56a2637cbd3037bdf598841c/library/alloc/src/boxed.rs:2070:9
        19: <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once
                   at /rustc/eeb90cda1969383f56a2637cbd3037bdf598841c/library/alloc/src/boxed.rs:2070:9
        20: std::sys::pal::unix::thread::Thread::new::thread_start
                   at /rustc/eeb90cda1969383f56a2637cbd3037bdf598841c/library/std/src/sys/pal/unix/thread.rs:108:17
        21: <unknown>
        22: <unknown>
  --> src/main.rs:38:41
   |
38 |     let node = Box::new(Node::new(Noop, vec![Box::new(Node::new(Noop, vec![]))]));
   |                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   = note: this error: internal compiler error originates in the macro `vec` (in Nightly builds, run with -Z macro-backtrace for more info)

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 1.81.0 (eeb90cda1 2024-09-04) running on x86_64-unknown-linux-gnu

note: compiler flags: --crate-type bin -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:
end of query stack
warning: `my_test` (bin "my_test") generated 2 warnings
error: could not compile `my_test` (bin "my_test"); 2 warnings emitted

[cyrgani]

More reduction:

trait Transform {
    type Output<'a>;
}

trait Propagate<Input> {}

fn new_node<T: Transform>(_c: Vec<Box<dyn for<'a> Propagate<<T as Transform>::Output<'a>>>>) -> T {
    todo!()
}

impl<Input, T> Propagate<Input> for T {}
struct Noop;

impl Transform for Noop {
    type Output<'a> = ();
}

fn main() {
    let _node: Noop = new_node(vec![Box::new(Noop)]);
}

[matthiaskrgr]

Regression in nightly-2021-07-17
commit[0] 2021-07-15: Auto merge of #83319 - tmiasko:packed-aligned, r=jackh726
commit[1] 2021-07-16: Auto merge of #86993 - jackh726:project-gat-binders, r=nikomatsakis
commit[2] 2021-07-16: Auto merge of #87177 - ehuss:update-cargo, r=ehuss
commit[3] 2021-07-16: Auto merge of #86662 - mockersf:fix-86620-link-unknown-location, r=jyn514
commit[4] 2021-07-16: Auto merge of #87182 - GuillaumeGomez:rollup-whwohua, r=GuillaumeGomez
commit[5] 2021-07-16: Auto merge of #87140 - camsteffen:pat-slice-refs, r=oli-obk
commit[6] 2021-07-16: Auto merge of #84623 - jackh726:gats-incomplete, r=nikomatsakis
commit[7] 2021-07-16: Auto merge of #87201 - GuillaumeGomez:rollup-4loi2q9, r=GuillaumeGomez
ERROR: no CI builds available between b1f8e27 and 74ef0c3 within last 167 days

I would guess either #86993 or #84623 ?

[ecryth]

I did come across #120811 and #110534 which may or may not be related? They both involve HRTBs, though no trait objects, and the regression date mentioned for the former one is later than when this regressed