ICE using min_type_alias_impl_trait with generators

[WorldSEnder]

Code

#![feature(min_type_alias_impl_trait, generator_trait, generators)]
use std::ops::{Generator};

pub trait GeneratorProviderAlt: Sized {
    type Gen: Generator<(), Return=(), Yield=()>;

    fn start(ctx: Context<Self>) -> Self::Gen;
}

pub struct Context<G: 'static + GeneratorProviderAlt> {
    // back-link to our generator state
    // In reality some other pointer type, but Box triggers the bug
    // Also in reality, points to a wrapper struct that only indirectly holds
    //   the generator state.
    link: Box<G::Gen>,
}

impl GeneratorProviderAlt for () {
    type Gen = impl Generator<(), Return=(), Yield=()>;
    fn start(ctx: Context<Self>) -> Self::Gen {
        move || {
            match ctx { _ => () } // make sure to use the context
            yield ();
        }
    }
}

playground link

I haven't gotten it to error without nightly features, so I believe it has to do with the generated enum for the Generator.

Meta

rustc --version --verbose:

rustc 1.55.0-nightly (952fdf2a1 2021-07-05)
binary: rustc
commit-hash: 952fdf2a1119affa1b37bcacb0c49cf9f0168ac8
commit-date: 2021-07-05
host: x86_64-unknown-linux-gnu
release: 1.55.0-nightly
LLVM version: 12.0.1

Error output

error: internal compiler error: compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs:150:13: type metadata for unique ID '324a3be6bacbf95688e06d88c8981eb0' is already in the `TypeMap`!

Backtrace

thread 'rustc' panicked at 'Box<dyn Any>', compiler/rustc_errors/src/lib.rs:1034:9
stack backtrace:
   0: std::panicking::begin_panic
   1: std::panic::panic_any
   2: rustc_errors::HandlerInner::bug
   3: rustc_errors::Handler::bug
   4: rustc_middle::ty::context::tls::with_opt
   5: rustc_middle::util::bug::opt_span_bug_fmt
   6: rustc_middle::util::bug::bug_fmt
   7: rustc_codegen_llvm::debuginfo::metadata::create_and_register_recursive_type_forward_declaration
   8: rustc_codegen_llvm::debuginfo::metadata::prepare_enum_metadata
   9: rustc_codegen_llvm::debuginfo::metadata::type_metadata
  10: rustc_codegen_llvm::debuginfo::<impl rustc_codegen_ssa::traits::debuginfo::DebugInfoMethods for rustc_codegen_llvm::context::CodegenCx>::dbg_scope_fn::get_function_signature
  11: rustc_codegen_llvm::debuginfo::<impl rustc_codegen_ssa::traits::debuginfo::DebugInfoMethods for rustc_codegen_llvm::context::CodegenCx>::dbg_scope_fn
  12: rustc_codegen_ssa::mir::codegen_mir
  13: rustc_codegen_ssa::base::codegen_instance
  14: <rustc_middle::mir::mono::MonoItem as rustc_codegen_ssa::mono_item::MonoItemExt>::define
  15: rustc_codegen_llvm::base::compile_codegen_unit::module_codegen
  16: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task
  17: rustc_codegen_llvm::base::compile_codegen_unit
  18: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_ssa::traits::backend::CodegenBackend>::codegen_crate
  19: rustc_interface::passes::QueryContext::enter
  20: rustc_interface::queries::Queries::ongoing_codegen
  21: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
  22: rustc_span::with_source_map
  23: rustc_interface::interface::create_compiler_and_run
  24: scoped_tls::ScopedKey<T>::set

---

As an aside, if one gets rid of the Box, this fails (kind of expected, though the error message could be improved) with

error[E0391]: cycle detected when computing layout of `[generator@src/lib.rs:21:9: 24:10]`
   |
   = note: ...which requires computing layout of `Context<()>`...
   = note: ...which again requires computing layout of `[generator@src/lib.rs:21:9: 24:10]`, completing the cycle
note: cycle used when optimizing MIR for `<impl at src/lib.rs:18:1: 26:2>::start`
  --> src/lib.rs:20:5

[Alexendoo]

No longer ICEs since #94261