rust-lang / rust-lang/rust

[ICE]: autodiff:not implemented

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C-bug F-autodiff I-ICE S-bug-has-test S-has-mcve T-compiler
Dominant language
Rust
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Forks
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PR metrics pending

Description

Code
//rustc
#![feature(autodiff)]
#[core::autodiff::autodiff_forward(fd_inner, Dual)]
fn f(_x: struct S<const N: usize, T>([T; N]) where T: Iterator<Item = u32>) {}
Meta

rustc --version --verbose:

rustc 1.99.0-nightly (ad3d0bc14 2026-07-31)
binary: rustc
commit-hash: ad3d0bc141a02cf446e384136d250a1f6950fed5
commit-date: 2026-07-31
host: x86_64-unknown-linux-gnu
release: 1.99.0-nightly
LLVM version: 22.1.8
Error output
error: expected type, found keyword `struct`
 --> ./Bug.rs:3:10
  |
3 | fn f(_x: struct S<const N: usize, T>([T; N]) where T: Iterator<Item = u32>) {}
  |          ^^^^^^ expected type

error: expected one of `:`, `@`, or `|`, found `>`
 --> ./Bug.rs:3:36
  |
3 | fn f(_x: struct S<const N: usize, T>([T; N]) where T: Iterator<Item = u32>) {}
  |                                    ^ expected one of `:`, `@`, or `|`

error: expected 2 activities, but found 1
 --> ./Bug.rs:2:1
  |
2 | #[core::autodiff::autodiff_forward(fd_inner, Dual)]
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Backtrace 

thread 'rustc' (3316818) panicked at /rustc-dev/ad3d0bc141a02cf446e384136d250a1f6950fed5/compiler/rustc_builtin_macros/src/autodiff.rs:566:26:
not implemented
stack backtrace:
   0:     0x7fc47d2c7a06 - <<std[83a5d38283ccaf0a]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[dd05a50edc8fb225]::fmt::Display>::fmt
   1:     0x7fc47da0a958 - core[dd05a50edc8fb225]::fmt::write
   2:     0x7fc47d2dcb4c - <std[83a5d38283ccaf0a]::sys::stdio::unix::Stderr as core[dd05a50edc8fb225]::io::write::Write>::write_fmt
   3:     0x7fc47d29aeaa - std[83a5d38283ccaf0a]::panicking::default_hook::{closure#0}
   4:     0x7fc47d2bb9b3 - std[83a5d38283ccaf0a]::panicking::default_hook
   5:     0x7fc47c22977b - std[83a5d38283ccaf0a]::panicking::update_hook::<alloc[fc3e6e3cedfc2867]::boxed::Box<rustc_driver_impl[4d341f08808842a2]::install_ice_hook::{closure#1}>>::{closure#0}
   6:     0x7fc47d2bbe52 - std[83a5d38283ccaf0a]::panicking::panic_with_hook
   7:     0x7fc47d29af94 - std[83a5d38283ccaf0a]::panicking::panic_handler::{closure#0}
   8:     0x7fc47d292b79 - std[83a5d38283ccaf0a]::sys::backtrace::__rust_end_short_backtrace::<std[83a5d38283ccaf0a]::panicking::panic_handler::{closure#0}, !>
   9:     0x7fc47d29c95d - __rustc[ebe1dd44d2b7d011]::rust_begin_unwind
  10:     0x7fc479f8bbdc - core[dd05a50edc8fb225]::panicking::panic_fmt
  11:     0x7fc47a37e4e2 - core[dd05a50edc8fb225]::panicking::panic
  12:     0x7fc47bff2da5 - rustc_builtin_macros[b6f3effaeb8c8780]::autodiff::llvm_enzyme::expand_with_mode
  13:     0x7fc47c009bf7 - <rustc_builtin_macros[b6f3effaeb8c8780]::autodiff::llvm_enzyme::expand_forward as rustc_expand[6767d9785d118df5]::base::MultiItemModifier>::expand
  14:     0x7fc47f1d7474 - <rustc_expand[6767d9785d118df5]::expand::MacroExpander>::fully_expand_fragment
  15:     0x7fc47f1d0180 - <rustc_expand[6767d9785d118df5]::expand::MacroExpander>::expand_crate
  16:     0x7fc47e305869 - rustc_interface[2c4fc24e203d38c5]::passes::resolver_for_lowering_raw
  17:     0x7fc47e305016 - rustc_query_impl[c5fbf8bbbde2d049]::query_impl::resolver_for_lowering_raw::invoke_provider_fn::__rust_begin_short_backtrace
  18:     0x7fc47ed145c1 - rustc_query_impl[c5fbf8bbbde2d049]::execution::try_execute_query::<rustc_middle[f5f43f33f8b944bb]::query::caches::SingleCache<rustc_middle[f5f43f33f8b944bb]::query::erase::ErasedData<[u8; 24usize]>>, false>
  19:     0x7fc47ed14338 - rustc_query_impl[c5fbf8bbbde2d049]::query_impl::resolver_for_lowering_raw::execute_query_non_incr::__rust_end_short_backtrace
  20:     0x7fc47ecb8676 - rustc_interface[2c4fc24e203d38c5]::interface::run_compiler::<(), rustc_driver_impl[4d341f08808842a2]::run_compiler::{closure#0}>::{closure#2}
  21:     0x7fc47ed223e4 - std[83a5d38283ccaf0a]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[2c4fc24e203d38c5]::util::run_in_thread_with_globals<rustc_interface[2c4fc24e203d38c5]::util::run_in_thread_pool_with_globals<rustc_interface[2c4fc24e203d38c5]::interface::run_compiler<(), rustc_driver_impl[4d341f08808842a2]::run_compiler::{closure#0}>::{closure#2}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  22:     0x7fc47ed221ad - <std[83a5d38283ccaf0a]::thread::lifecycle::spawn_unchecked<rustc_interface[2c4fc24e203d38c5]::util::run_in_thread_with_globals<rustc_interface[2c4fc24e203d38c5]::util::run_in_thread_pool_with_globals<rustc_interface[2c4fc24e203d38c5]::interface::run_compiler<(), rustc_driver_impl[4d341f08808842a2]::run_compiler::{closure#0}>::{closure#2}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[dd05a50edc8fb225]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  23:     0x7fc47ed2e43a - <std[83a5d38283ccaf0a]::sys::thread::unix::Thread>::new::thread_start
  24:     0x7fc47828aaa4 - start_thread
                               at ./nptl/pthread_create.c:447:8
  25:     0x7fc478317c6c - clone3
                               at ./misc/../sysdeps/unix/sysv/linux/x86_64/clone3.S:78:0
  26:                0x0 - <unknown>

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 `/home/bug/rustc-ice-2026-08-01T10_33_31-3316808.txt` to your bug report

note: rustc 1.99.0-nightly (ad3d0bc14 2026-07-31) running on x86_64-unknown-linux-gnu

query stack during panic:
#0 [resolver_for_lowering_raw] getting the resolver for lowering
end of query stack

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with the reproducer and the panic location in compiler/rustc_builtin_macros/src/autodiff.rs:566, especially llvm_enzyme::expand_with_mode. Run the example with the reported nightly compiler, then trace how the autodiff attribute handles this malformed generic parameter. Done should include regression coverage for the reproducer and ensure compilation no longer reaches an unexpected panic.

Written by the indexing model from the issue text.

Assessment

Tech stack
rust
Domain
compilers
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Active
Clarity
Mostly clear
Newbie friendliness
50/100

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