Cannot turn `UnevaluatedConst` into `AliasTy`

[sigurd4]

Crate name

option_trait

Build failure link

https://docs.rs/crate/option_trait/1.0.0/builds/1596995

Additional details

It builds fine on my machine. Same rust nightly version too.

I think it's due to the type alias Copied that relies on a possibly not well formed associated type in the trait private::_Copied. At least that's the only case where i've used a type alias throughout the project (located in lib.rs)

[sigurd4]

Never mind. I got rid of the type alias, and avoided doing specialization in private::_Copied, yet i get the same error on docs.rs. The original hypothesis i had for why it wont build was wrong, so now i have no idea.

Build failure link (second attempt, same error)

https://docs.rs/crate/option_trait/1.0.2/builds/1597040

[sigurd4]

Managed to make it build on docs.rs by excluding feature opt_cell. So clearly the problem is located somewhere in opt_cell.rs. For now i'll just exclude the feature in the documentation

[syphar]

this is odd, especially when you are using the same nightly version. You can look up the nightly version we're using under https://docs.rs/about/builds .

What sometimes helps is running the doc-build with very similar arguments as we do it: https://github.com/dtolnay/cargo-docs-rs

[sigurd4]

Thanks. That's a very useful tool. I ran cargo docs-rs and got the same error. Does not happen if i run cargo build normally. If i omit feature opt_cell from the crate, cargo docs-rs runs fine without errors.

[sigurd4]

So it's clearly not a resource limit issue, it's probably due to using experimental rust language features like specialization i think. I suspect it might fail on the specialization i do on the trait _Spec. I'll try to isolate the problem.

[sigurd4]

Weird... I tried just commenting out everything in the opt_cell.rs file except the following and i still got the same error, even after doing cargo clean.

pub struct OptCell<T>(T);

Removed the const expr and the specialized type too, yet the same error happens

[sigurd4]

If i make a similar struct in another clean project, no error occurs, so it has to be something about my repo specifically. Very strange. It happens only when the file opt_cell.rs is included.

And i can even replace the whole file contents with this:

struct Whatever(u32);

And i get the same error. But doing so in a clean project does not produce the error.

[sigurd4]

Rust ICE when doing cargo docs-rs:

thread 'rustc' panicked at /rustc/426d1734238e3c5f52e935ba4f617f3a9f43b59d/compiler/rustc_type_ir/src/predicate.rs:532:17:
Cannot turn `UnevaluatedConst` into `AliasTy`
stack backtrace:
   0:     0x7db52efcd1a5 - std::backtrace::Backtrace::create::h2021bf191a8739ac
   1:     0x7db52d4a4555 - std::backtrace::Backtrace::force_capture::h1c4a4f7d7b3cc85e
   2:     0x7db52c6306fe - std[9670bf84f1ec365]::panicking::update_hook::<alloc[6b9af05f37cecee8]::boxed::Box<rustc_driver_impl[e843f2e3b8b39cd5]::install_ice_hook::{closure#0}>>::{closure#0}
   3:     0x7db52d4bc4c8 - std::panicking::rust_panic_with_hook::h1e4476f399791006
   4:     0x7db52d4bc186 - std::panicking::begin_panic_handler::{{closure}}::hd8b76955e18606db
   5:     0x7db52d4b9e69 - std::sys::backtrace::__rust_end_short_backtrace::hc35e6bbd7a6cbefa
   6:     0x7db52d4bbe7d - rust_begin_unwind
   7:     0x7db52a19c070 - core::panicking::panic_fmt::hf53ce36a54419534
   8:     0x5b84d65867dc - rustdoc[681614ec0d172b40]::clean::clean_predicate
   9:     0x5b84d658c056 - rustdoc[681614ec0d172b40]::clean::clean_ty_generics
  10:     0x5b84d657e7ee - rustdoc[681614ec0d172b40]::clean::utils::synthesize_auto_trait_and_blanket_impls
  11:     0x5b84d66b956c - <rustdoc[681614ec0d172b40]::passes::collect_trait_impls::SyntheticImplCollector as rustdoc[681614ec0d172b40]::visit::DocVisitor>::visit_item
  12:     0x5b84d66b96ca - <rustdoc[681614ec0d172b40]::passes::collect_trait_impls::SyntheticImplCollector as rustdoc[681614ec0d172b40]::visit::DocVisitor>::visit_item
  13:     0x5b84d66b96ca - <rustdoc[681614ec0d172b40]::passes::collect_trait_impls::SyntheticImplCollector as rustdoc[681614ec0d172b40]::visit::DocVisitor>::visit_item
  14:     0x5b84d66b5cf4 - rustdoc[681614ec0d172b40]::passes::collect_trait_impls::collect_trait_impls
  15:     0x5b84d65b1083 - rustdoc[681614ec0d172b40]::core::run_global_ctxt
  16:     0x5b84d645f0be - rustc_interface[b890ba4e2d030cf2]::passes::create_and_enter_global_ctxt::<(), rustdoc[681614ec0d172b40]::main_args::{closure#2}::{closure#0}>::{closure#2}::{closure#0}
  17:     0x5b84d646c9a9 - <rustc_interface[b890ba4e2d030cf2]::passes::create_and_enter_global_ctxt<(), rustdoc[681614ec0d172b40]::main_args::{closure#2}::{closure#0}>::{closure#2} as core[3afde4322c674bff]::ops::function::FnOnce<(&rustc_session[f34cc6760836d978]::session::Session, rustc_middle[b475e519b0252996]::ty::context::CurrentGcx, &std[9670bf84f1ec365]::sync::once_lock::OnceLock<rustc_middle[b475e519b0252996]::ty::context::GlobalCtxt>, &rustc_data_structures[ad01a8bbeb531a41]::sync::worker_local::WorkerLocal<rustc_middle[b475e519b0252996]::arena::Arena>, &rustc_data_structures[ad01a8bbeb531a41]::sync::worker_local::WorkerLocal<rustc_hir[38f3bbf9692ea739]::Arena>, rustdoc[681614ec0d172b40]::main_args::{closure#2}::{closure#0})>>::call_once::{shim:vtable#0}
  18:     0x5b84d6458908 - rustc_interface[b890ba4e2d030cf2]::interface::run_compiler::<(), rustdoc[681614ec0d172b40]::main_args::{closure#2}>::{closure#1}
  19:     0x5b84d63dde29 - std[9670bf84f1ec365]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[b890ba4e2d030cf2]::util::run_in_thread_with_globals<rustc_interface[b890ba4e2d030cf2]::util::run_in_thread_pool_with_globals<rustc_interface[b890ba4e2d030cf2]::interface::run_compiler<(), rustdoc[681614ec0d172b40]::main_args::{closure#2}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  20:     0x5b84d64688ee - <<std[9670bf84f1ec365]::thread::Builder>::spawn_unchecked_<rustc_interface[b890ba4e2d030cf2]::util::run_in_thread_with_globals<rustc_interface[b890ba4e2d030cf2]::util::run_in_thread_pool_with_globals<rustc_interface[b890ba4e2d030cf2]::interface::run_compiler<(), rustdoc[681614ec0d172b40]::main_args::{closure#2}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[3afde4322c674bff]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  21:     0x7db52ea5df81 - std::sys::pal::unix::thread::Thread::new::thread_start::h98893ae41d9b5d0a
  22:     0x7db528db439d - <unknown>
  23:     0x7db528e3949c - <unknown>
  24:                0x0 - <unknown>


rustc version: 1.85.0-nightly (426d17342 2024-12-21)
platform: x86_64-unknown-linux-gnu

query stack during panic:
end of query stack

[syphar]

Rust ICE when doing cargo docs-rs:

can you report this to the compiler repo?

[sigurd4]

Done https://github.com/rust-lang/rust/issues/134775