Compiler panic during "evaluating trait selection obligation"

[PaulWagener]

I encountered a compiler error, though it doesn't happen all the time. Even with just adding some meaningless whitespace I only get the error around 50% of the time. Trying to minimize it the panic doesn't happen anymore :(

Code

use brush_render::MainBackend;
use brush_render::camera::Camera;
use brush_render::gaussian_splats::Splats;
use brush_train::config::TrainConfig;
use brush_train::train::SplatTrainer;
use burn_autodiff::Autodiff;
use burn_core::module::AutodiffModule;
use burn_wgpu::WgpuDevice;
use glam::f32::vec3;
use glam::u32::uvec2;

type DiffBackend = Autodiff<MainBackend>;

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    let device = WgpuDevice::DefaultDevice;

    let splats =
        Splats::<DiffBackend>::from_raw(vec![0.0, 0.0, 0.0], None, None, None, None, &device);

    let camera = Camera {
        fov_x: 10.0,
        fov_y: 10.0,
        center_uv: Default::default(),
        position: Default::default(),
        rotation: Default::default(),
    };

    let (rgb, _) = splats
        .valid()
        .render(&camera, uvec2(1, 1), vec3(0.0, 0.0, 0.0), None);

    // Export rgb
    dbg!(rgb.dtype());
    dbg!(rgb.into_data().dtype);

    let mut splat_trainer = SplatTrainer::new(&TrainConfig::default(), &device, splats).await;
    //splat_trainer.step()

    println!("Einde");
    Ok(())
}

Meta

rustc --version --verbose:

rustc 1.93.0-nightly (1be6b13be 2025-11-26)
binary: rustc
commit-hash: 1be6b13be73dc12e98e51b403add4c41a0b77759
commit-date: 2025-11-26
host: aarch64-apple-darwin
release: 1.93.0-nightly
LLVM version: 21.1.5

Error output

error: internal compiler error: encountered incremental compilation error with evaluate_obligation(fcc672b079f4c123-2a16a3fcd11c62)
  |
  = note: please follow the instructions below to create a bug report with the provided information
  = note: for incremental compilation bugs, having a reproduction is vital
  = note: an ideal reproduction consists of the code before and some patch that then triggers the bug when applied and compiled again
  = note: as a workaround, you can run `cargo clean -p true_ortho` or `cargo clean` to allow your project to compile

thread 'rustc' (4817783) panicked at /rustc-dev/1be6b13be73dc12e98e51b403add4c41a0b77759/compiler/rustc_query_system/src/query/plumbing.rs:752:9:
Found unstable fingerprints for evaluate_obligation(fcc672b079f4c123-2a16a3fcd11c62): Err(Canonical)
stack backtrace:
   0: __rustc::rust_begin_unwind
   1: core::panicking::panic_fmt
   2: rustc_query_system::query::plumbing::incremental_verify_ich_failed::<rustc_middle::ty::context::TyCtxt>
   3: rustc_query_system::query::plumbing::incremental_verify_ich::<rustc_middle::ty::context::TyCtxt, rustc_middle::query::erase::Erased<[u8; 2]>>
   4: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::DefaultCache<rustc_type_ir::canonical::CanonicalQueryInput<rustc_middle::ty::context::TyCtxt, rustc_middle::ty::ParamEnvAnd<rustc_middle::ty::predicate::Predicate>>, rustc_middle::query::erase::Erased<[u8; 2]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, true>
   5: <rustc_infer::infer::InferCtxt as rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt>::evaluate_obligation
   6: <rustc_infer::infer::InferCtxt as rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt>::evaluate_obligation_no_overflow
   7: rustc_trait_selection::traits::type_known_to_meet_bound_modulo_regions
   8: rustc_ty_utils::common_traits::is_item_raw
      [... omitted 2 frames ...]
   9: <rustc_middle::ty::Ty>::is_sized
  10: rustc_ty_utils::layout::layout_of
      [... omitted 2 frames ...]
  11: <rustc_middle::ty::layout::LayoutCx as rustc_middle::ty::layout::LayoutOf>::spanned_layout_of
  12: rustc_ty_utils::abi::fn_abi_new_uncached::{closure#2}
  13: <core::iter::adapters::GenericShunt<core::iter::adapters::map::Map<core::iter::adapters::enumerate::Enumerate<core::iter::adapters::chain::Chain<core::iter::adapters::chain::Chain<core::iter::adapters::copied::Copied<core::slice::iter::Iter<rustc_middle::ty::Ty>>, core::iter::adapters::copied::Copied<core::slice::iter::Iter<rustc_middle::ty::Ty>>>, core::option::IntoIter<rustc_middle::ty::Ty>>>, rustc_ty_utils::abi::fn_abi_new_uncached::{closure#3}>, core::result::Result<core::convert::Infallible, &rustc_middle::ty::layout::FnAbiError>> as core::iter::traits::iterator::Iterator>::next
  14: rustc_ty_utils::abi::fn_abi_new_uncached
  15: rustc_ty_utils::abi::fn_abi_of_instance
      [... omitted 2 frames ...]
  16: <rustc_codegen_llvm::context::GenericCx<rustc_codegen_llvm::context::FullCx> as rustc_middle::ty::layout::FnAbiOf>::fn_abi_of_instance
  17: <rustc_codegen_llvm::context::GenericCx<rustc_codegen_llvm::context::FullCx> as rustc_codegen_ssa::traits::declare::PreDefineCodegenMethods>::predefine_fn
  18: rustc_codegen_llvm::base::compile_codegen_unit::module_codegen
  19: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_ssa::traits::backend::ExtraBackendMethods>::compile_codegen_unit
  20: rustc_codegen_ssa::base::codegen_crate::<rustc_codegen_llvm::LlvmCodegenBackend>
  21: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_ssa::traits::backend::CodegenBackend>::codegen_crate
  22: <rustc_interface::queries::Linker>::codegen_and_build_linker
  23: rustc_interface::passes::create_and_enter_global_ctxt::<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>
  24: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
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: please attach the file at `/Users/paul/mastools/rustc-ice-2025-11-27T14_15_00-22368.txt` to your bug report
note: compiler flags: --crate-type bin -C embed-bitcode=no -C debuginfo=2 -C split-debuginfo=unpacked -C incremental=[REDACTED]
note: some of the compiler flags provided by cargo are hidden
query stack during panic:
#0 [evaluate_obligation] evaluating trait selection obligation `lpips::VggBlockRecord<burn_autodiff::backend::Autodiff<burn_fusion::backend::Fusion<burn_cubecl::backend::CubeBackend<cubecl_wgpu::runtime::WgpuRuntime, f32, i32, u32>>>>: core::marker::Sized`
#1 [is_sized_raw] computing whether `lpips::VggBlockRecord<burn_autodiff::backend::Autodiff<burn_fusion::backend::Fusion<burn_cubecl::backend::CubeBackend<cubecl_wgpu::runtime::WgpuRuntime, f32, i32, u32>>>>` is `Sized`
#2 [layout_of] computing layout of `*mut lpips::VggBlockRecord<burn_autodiff::backend::Autodiff<burn_fusion::backend::Fusion<burn_cubecl::backend::CubeBackend<cubecl_wgpu::runtime::WgpuRuntime, f32, i32, u32>>>>`
#3 [fn_abi_of_instance] computing call ABI of `core::ptr::drop_in_place::<lpips::VggBlockRecord<burn_autodiff::backend::Autodiff<burn_fusion::backend::Fusion<burn_cubecl::backend::CubeBackend<cubecl_wgpu::runtime::WgpuRuntime, f32, i32, u32>>>>> - shim(Some(lpips::VggBlockRecord<burn_autodiff::backend::Autodiff<burn_fusion::backend::Fusion<burn_cubecl::backend::CubeBackend<cubecl_wgpu::runtime::WgpuRuntime, f32, i32, u32>>>>))`
end of query stack

Backtrace

rustc-ice-2025-11-27T14_15_00-22368.txt
Cargo.lock.zip

[aviralgarg05]

I would like to solve this issue

[bjorn3]

Getting a reliable reproducer would be a first step in fixing this. Given that this is an incr comp issue, a reproducer would be a combination of some source (+ Cargo.toml and Cargo.lock if using external dependencies) you can compile after cargo clean and a change you make before compiling again that reproduces the error. Or perhaps if we are lucky, a single compilation with -Zincremental-verify-ich is enough.

[aviralgarg05]

I'll create a pr for review