ICE: `features not available at this point in the compiler`

[matthiaskrgr]

snippet:

#![cfg(not(version()))]

Version information

rustc 1.90.0-nightly (e27f16a49 2025-07-15)
binary: rustc
commit-hash: e27f16a499074ba9a87f7f7641d9f64c572863bc
commit-date: 2025-07-15
host: x86_64-unknown-linux-gnu
release: 1.90.0-nightly
LLVM version: 20.1.8

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc

Program output

thread 'rustc' panicked at /rustc-dev/e27f16a499074ba9a87f7f7641d9f64c572863bc/compiler/rustc_attr_parsing/src/context.rs:672:23:
features not available at this point in the compiler
stack backtrace:
   0:     0x78fee8df6c43 - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::h0f4d7c05d57d335b
   1:     0x78fee96026f7 - core::fmt::write::ha3410023fed29f5d
   2:     0x78fee8dec883 - std::io::Write::write_fmt::h6e8ec0f1a7e67c48
   3:     0x78fee8df6aa2 - std::sys::backtrace::BacktraceLock::print::h17decb4264124f62
   4:     0x78fee8dfa547 - std::panicking::default_hook::{{closure}}::hd26dc22507e42f6c
   5:     0x78fee8dfa0ab - std::panicking::default_hook::hb49d1e0099f784eb
   6:     0x78fee7e90953 - std[d06d6d9fc80641c0]::panicking::update_hook::<alloc[1af2d9a3699601a0]::boxed::Box<rustc_driver_impl[60bc6dfbffcb9653]::install_ice_hook::{closure#1}>>::{closure#0}
   7:     0x78fee8dfad8e - std::panicking::rust_panic_with_hook::he58b5a36608d6207
   8:     0x78fee8dfaa8a - std::panicking::begin_panic_handler::{{closure}}::hc9d8cd4b2ad4525b
   9:     0x78fee8df7109 - std::sys::backtrace::__rust_end_short_backtrace::h36675efd28bcafb3
  10:     0x78fee8dfa76d - __rustc[6da1d1fc3ed0e853]::rust_begin_unwind
  11:     0x78fee54f2d50 - core::panicking::panic_fmt::h9b0c040fa6b46ce5
  12:     0x78fee6a6ee0b - core::option::expect_failed::h769bba545722f10c
  13:     0x78feea2f66de - rustc_attr_parsing[e173394a2c5293f5]::attributes::cfg::parse_cfg_entry::<rustc_attr_parsing[e173394a2c5293f5]::context::Early>
  14:     0x78feea2f5b1d - rustc_attr_parsing[e173394a2c5293f5]::attributes::cfg::parse_cfg_entry::<rustc_attr_parsing[e173394a2c5293f5]::context::Early>
  15:     0x78feea2f6c5a - <rustc_expand[38b4ce7acc9d20d2]::config::StripUnconfigured>::cfg_true
  16:     0x78feea3a2c44 - rustc_expand[38b4ce7acc9d20d2]::config::pre_configure_attrs
  17:     0x78feea91e19e - rustc_interface[d7c71b782988ecd7]::interface::run_compiler::<(), rustc_driver_impl[60bc6dfbffcb9653]::run_compiler::{closure#0}>::{closure#1}
  18:     0x78feea7c58f8 - std[d06d6d9fc80641c0]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[d7c71b782988ecd7]::util::run_in_thread_with_globals<rustc_interface[d7c71b782988ecd7]::util::run_in_thread_pool_with_globals<rustc_interface[d7c71b782988ecd7]::interface::run_compiler<(), rustc_driver_impl[60bc6dfbffcb9653]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  19:     0x78feea7c55d6 - <<std[d06d6d9fc80641c0]::thread::Builder>::spawn_unchecked_<rustc_interface[d7c71b782988ecd7]::util::run_in_thread_with_globals<rustc_interface[d7c71b782988ecd7]::util::run_in_thread_pool_with_globals<rustc_interface[d7c71b782988ecd7]::interface::run_compiler<(), rustc_driver_impl[60bc6dfbffcb9653]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[8fc6db251fcc4b36]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  20:     0x78feea7cb6bd - std::sys::pal::unix::thread::Thread::new::thread_start::h506ffcc7cb689135
  21:     0x78fee409b7eb - <unknown>
  22:     0x78fee411f18c - <unknown>
  23:                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: rustc 1.90.0-nightly (e27f16a49 2025-07-15) running on x86_64-unknown-linux-gnu

query stack during panic:
end of query stack

[matthiaskrgr]

#143460 cc @JonathanBrouwer

[JonathanBrouwer]

@rustbot claim
Ah, thanks for finding this, I'll fix it!

Just out of interest, how are you finding these? Are you fuzzing these somehow, or are you just really good at breaking my work :P
If you're fuzzing, do you have to teach the fuzzer about the structure of these attributes somehow?

[asquared31415]

Matthias is known for fuzzing and running things in glacier (a collection of known/past ICE) with small adjustments, so I suspect it is indeed fuzzed or a regression of known code that was not actually put in the test suite when it was fixed last time.

Regarding how, there's a lot of work in making fuzzers that understand syntax and I don't know the full extent but I know it's like a decade+ of thesis level projects. Sometimes it's possible to do small modifications to the AST to produce new code for fuzzing.