ICE when getting the size of a struct containing itself in an odd way

[pitust]

Code

trait A<Y, N> {
    type B;
}
type MaybeBox<T> = <T as A<T, Box<T>>>::B;
struct P {
    t: MaybeBox<P>
}
impl<Y, N> A<Y, N> for P {
    type B = N;
}
fn main() {
    let t: MaybeBox<P>;
}

Meta

rustc --version --verbose:

# nightly
rustc 1.52.0-nightly (9b471a3f5 2021-02-19)
binary: rustc
commit-hash: 9b471a3f5fe57e5c6e08acf665f2094422415a3d
commit-date: 2021-02-19
host: aarch64-apple-darwin
release: 1.52.0-nightly
LLVM version: 11.0.1
# stable
rustc 1.50.0 (cb75ad5db 2021-02-10)
binary: rustc
commit-hash: cb75ad5db02783e8b0222fee363c5f63f7e2cf5b
commit-date: 2021-02-10
host: aarch64-apple-darwin
release: 1.50.0

Error output

# nightly
warning: unused variable: `t`
  --> src/ice.rs:12:9
   |
12 |     let t: MaybeBox<P>;
   |         ^ help: if this is intentional, prefix it with an underscore: `_t`
   |
   = note: `#[warn(unused_variables)]` on by default

error: internal compiler error: compiler/rustc_codegen_llvm/src/context.rs:778:17: failed to get layout for `Box<P>`: the type `std::alloc::Global` has an unknown layout

thread 'rustc' panicked at 'Box<Any>', /rustc/9b471a3f5fe57e5c6e08acf665f2094422415a3d/library/std/src/panic.rs:59:5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

note: 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: rustc 1.52.0-nightly (9b471a3f5 2021-02-19) running on aarch64-apple-darwin

query stack during panic:
end of query stack
error: aborting due to previous error; 1 warning emitted

# stable
warning: unused variable: `t`
  --> src/ice.rs:12:9
   |
12 |     let t: MaybeBox<P>;
   |         ^ help: if this is intentional, prefix it with an underscore: `_t`
   |
   = note: `#[warn(unused_variables)]` on by default

error: internal compiler error: compiler/rustc_codegen_llvm/src/context.rs:896:17: failed to get layout for `Box<P>`: the type `std::alloc::Global` has an unknown layout

thread 'rustc' panicked at 'Box<Any>', compiler/rustc_errors/src/lib.rs:958:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

note: 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: rustc 1.50.0 (cb75ad5db 2021-02-10) running on aarch64-apple-darwin

query stack during panic:
end of query stack
error: aborting due to previous error; 1 warning emitted

Backtrace

warning: unused variable: `t`
  --> src/ice.rs:12:9
   |
12 |     let t: MaybeBox<P>;
   |         ^ help: if this is intentional, prefix it with an underscore: `_t`
   |
   = note: `#[warn(unused_variables)]` on by default

error: internal compiler error: compiler/rustc_codegen_llvm/src/context.rs:778:17: failed to get layout for `Box<P>`: the type `std::alloc::Global` has an unknown layout

thread 'rustc' panicked at 'Box<Any>', /rustc/9b471a3f5fe57e5c6e08acf665f2094422415a3d/library/std/src/panic.rs:59:5
stack backtrace:
   0:        0x108462844 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h043213eec1d948a5
   1:        0x1084befc4 - core::fmt::write::hf53968076cf4f14e
   2:        0x108456ad0 - std::io::Write::write_fmt::h28b0246eee567fa4
   3:        0x108466074 - std::panicking::default_hook::{{closure}}::h8d1966a8d6a15176
   4:        0x108465b9c - std::panicking::default_hook::h9e61206a690d3893
   5:        0x101529fc0 - rustc_driver::report_ice::he031b89daf683be2
   6:        0x1084667ac - std::panicking::rust_panic_with_hook::hd1308496ca12fe75
   7:        0x104f815b4 - std::panicking::begin_panic::{{closure}}::hcba543a8c5f1d08d
   8:        0x104f81524 - std::sys_common::backtrace::__rust_end_short_backtrace::h362c2d8a9e8d5298
   9:        0x105331b68 - std::panicking::begin_panic::h93e3158113bdbc60
  10:        0x104f6ff2c - std::panic::panic_any::h726732c1e110a4ed
  11:        0x104f75ed0 - rustc_errors::HandlerInner::bug::h3b8f241f53eaf369
  12:        0x104f74844 - rustc_errors::Handler::bug::h8de1066ed91b927d
  13:        0x104bfaea0 - rustc_middle::util::bug::opt_span_bug_fmt::{{closure}}::h44d18bd8b9b96860
  14:        0x104bfa4f4 - rustc_middle::ty::context::tls::with_opt::{{closure}}::h127e943ea1d82039
  15:        0x104bfa4c4 - rustc_middle::ty::context::tls::with_opt::h15355bc739995ab5
  16:        0x104bfadfc - rustc_middle::util::bug::opt_span_bug_fmt::hd81b691c1ebfe316
  17:        0x10531cf90 - rustc_middle::util::bug::bug_fmt::hed974c89fe586787
  18:        0x101854be4 - <rustc_codegen_llvm::context::CodegenCx as rustc_target::abi::LayoutOf>::spanned_layout_of::{{closure}}::hc33838b90d61229a
  19:        0x101854ae8 - <rustc_codegen_llvm::context::CodegenCx as rustc_target::abi::LayoutOf>::spanned_layout_of::h1d6e88314f230529
  20:        0x101819b88 - rustc_codegen_ssa::mir::analyze::non_ssa_locals::h7533078a57869e49
  21:        0x1017a7b70 - rustc_codegen_ssa::mir::codegen_mir::he40696223aa51736
  22:        0x1018295e8 - rustc_codegen_ssa::base::codegen_instance::h5db39f5bdef05836
  23:        0x10186bc54 - <rustc_middle::mir::mono::MonoItem as rustc_codegen_ssa::mono_item::MonoItemExt>::define::h46f0ab8e9a6af95e
  24:        0x101766420 - rustc_codegen_llvm::base::compile_codegen_unit::module_codegen::h8383c56c09ee28e5
  25:        0x10187d154 - rustc_query_system::dep_graph::graph::DepGraph<K>::with_task::hb61eed6b6daccc43
  26:        0x101765e54 - rustc_codegen_llvm::base::compile_codegen_unit::hc6ff00cd13bf2ad7
  27:        0x101840568 - <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_ssa::traits::backend::CodegenBackend>::codegen_crate::hc0cff821987c1e1a
  28:        0x1016dd278 - rustc_interface::queries::Queries::ongoing_codegen::ha2a71002e07ad1b7
  29:        0x10154aa30 - rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter::h79312bfd55dc88a9
  30:        0x10152c7a4 - rustc_span::with_source_map::h6e88bbd7481b3eff
  31:        0x101543f2c - scoped_tls::ScopedKey<T>::set::hae52353f87af177a
  32:        0x10154ccbc - std::sys_common::backtrace::__rust_begin_short_backtrace::hd3d5294404312cd1
  33:        0x1014e1094 - core::ops::function::FnOnce::call_once{{vtable.shim}}::h6426353783274c03
  34:        0x108472290 - std::sys::unix::thread::Thread::new::thread_start::h5458ae4a1bb3b8f6
  35:        0x1a085e06c - _pthread_kill

note: 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: rustc 1.52.0-nightly (9b471a3f5 2021-02-19) running on aarch64-apple-darwin

query stack during panic:
end of query stack
error: aborting due to previous error; 1 warning emitted

The bug happens in here:

rust/compiler/rustc_codegen_llvm/src/context.rs

Line 785 in 4099208

bug!("failed to get layout for `{}`: {}", ty, e)

.

It happens due to an assertion that the error is a LayoutError::SizeOverflow which it isn't i guess.
I think it's related to a type being contained within itself, but not really.

[LeSeulArtichaut]

This ICEs since 1.49.0. In 1.48.0, rustc gives the following errors:

rror[E0275]: overflow evaluating the requirement `P: Sized`
 --> <source>:6:8
  |
6 |     t: MaybeBox<P>
  |        ^^^^^^^^^^^
  |
  = note: required because of the requirements on the impl of `A<P, Box<P>>` for `P`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0275`.
ASM generation compiler returned: 1
error[E0275]: overflow evaluating the requirement `P: Sized`
 --> <source>:6:8
  |
6 |     t: MaybeBox<P>
  |        ^^^^^^^^^^^
  |
  = note: required because of the requirements on the impl of `A<P, Box<P>>` for `P`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0275`.

[apiraino]

bisection result

searched nightlies: from nightly-2020-08-01 to nightly-2021-03-10
regressed nightly: nightly-2020-10-07
searched commits: from a1dfd24 to 98edd1f
regressed commit: 08e2d46

bisected with cargo-bisect-rustc v0.6.0

Host triple: x86_64-unknown-linux-gnu
Reproduce with:

cargo bisect-rustc --start=2020-08-01 --regress=ice 

[apiraino]

Assigning P-medium as discussed as part of the Prioritization Working Group procedure and removing I-prioritize.

@rustbot label -I-prioritize +P-medium

[FabianWolff]

Slightly simplified:

trait A<Y> { type B; }
type MaybeBox<T> = <T as A<T>>::B;

struct P { _t: MaybeBox<P> }

impl<Y> A<Y> for P {
    type B = Box<P>;
}

fn main() {
    let _t: MaybeBox<P>;
}

[Alexendoo]

No longer ICEs since #85868