ICE on invalid `rustc_layout_scalar_valid_range_start` attribute

[chengniansun]

Code

#![feature(rustc_attrs)]
use std::num::NonZeroU8;
#[rustc_layout_scalar_valid_range_start(C)]
union MaybeUninit<T: Copy> {
    uninit: (),
    init: T,
}
const UNINIT: NonZeroU8 = MaybeUninit { uninit: () }.init;

Meta

rustc --version --verbose:

rustc 1.52.0-nightly (3a5d45f68 2021-03-09)
binary: rustc
commit-hash: 3a5d45f68cadc8fff4fbb557780f92b403b19c19
commit-date: 2021-03-09
host: x86_64-unknown-linux-gnu
release: 1.52.0-nightly
LLVM version: 12.0.0

Error output

thread 'rustc' panicked at 'attribute takes lit', compiler/rustc_middle/src/ty/context.rs:1095:38
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

error: internal compiler error: unexpected panic

note: 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: rustc 1.52.0-nightly (3a5d45f68 2021-03-09) running on x86_64-unknown-linux-gnu

note: compiler flags: --crate-type staticlib

query stack during panic:
#0 [unsafety_check_result] unsafety-checking `UNINIT`
#1 [mir_const] processing MIR for `UNINIT`
end of query stack

Backtrace

thread 'rustc' panicked at 'attribute takes lit', compiler/rustc_middle/src/ty/context.rs:1095:38
stack backtrace:
   0: rust_begin_unwind
             at /rustc/3a5d45f68cadc8fff4fbb557780f92b403b19c19/library/std/src/panicking.rs:493:5
   1: core::panicking::panic_fmt
             at /rustc/3a5d45f68cadc8fff4fbb557780f92b403b19c19/library/core/src/panicking.rs:92:14
   2: core::option::expect_failed
             at /rustc/3a5d45f68cadc8fff4fbb557780f92b403b19c19/library/core/src/option.rs:1293:5
   3: rustc_middle::ty::context::TyCtxt::layout_scalar_valid_range::{{closure}}
   4: rustc_middle::ty::context::TyCtxt::layout_scalar_valid_range
   5: <rustc_mir::transform::check_unsafety::UnsafetyChecker as rustc_middle::mir::visit::Visitor>::visit_rvalue
   6: rustc_mir::transform::check_unsafety::unsafety_check_result
   7: core::ops::function::FnOnce::call_once
   8: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
   9: rustc_data_structures::stack::ensure_sufficient_stack
  10: rustc_query_system::query::plumbing::force_query_with_job
  11: rustc_query_system::query::plumbing::get_query_impl
  12: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::unsafety_check_result
  13: rustc_mir::transform::mir_const
  14: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  15: rustc_data_structures::stack::ensure_sufficient_stack
  16: rustc_query_system::query::plumbing::force_query_with_job
  17: rustc_query_system::query::plumbing::get_query_impl
  18: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::mir_const
  19: rustc_mir::transform::mir_const_qualif
  20: core::ops::function::FnOnce::call_once
  21: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  22: rustc_data_structures::stack::ensure_sufficient_stack
  23: rustc_query_system::query::plumbing::force_query_with_job
  24: rustc_query_system::query::plumbing::get_query_impl
  25: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::mir_const_qualif
  26: rustc_mir::transform::mir_promoted
  27: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  28: rustc_data_structures::stack::ensure_sufficient_stack
  29: rustc_query_system::query::plumbing::force_query_with_job
  30: rustc_query_system::query::plumbing::get_query_impl
  31: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::mir_promoted
  32: rustc_mir::borrow_check::mir_borrowck
  33: core::ops::function::FnOnce::call_once
  34: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  35: rustc_data_structures::stack::ensure_sufficient_stack
  36: rustc_query_system::query::plumbing::force_query_with_job
  37: rustc_query_system::query::plumbing::get_query_impl
  38: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::mir_borrowck
  39: rustc_middle::ty::<impl rustc_middle::ty::context::TyCtxt>::par_body_owners
  40: rustc_interface::passes::analysis
  41: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  42: rustc_data_structures::stack::ensure_sufficient_stack
  43: rustc_query_system::query::plumbing::force_query_with_job
  44: rustc_query_system::query::plumbing::get_query_impl
  45: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::analysis
  46: rustc_interface::passes::QueryContext::enter
  47: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
  48: rustc_span::with_source_map
  49: rustc_interface::interface::create_compiler_and_run
  50: rustc_span::with_session_globals
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

error: internal compiler error: unexpected panic

note: 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: rustc 1.52.0-nightly (3a5d45f68 2021-03-09) running on x86_64-unknown-linux-gnu

note: compiler flags: --crate-type staticlib

query stack during panic:
#0 [unsafety_check_result] unsafety-checking `UNINIT`
#1 [mir_const] processing MIR for `UNINIT`
#2 [mir_const_qualif] const checking `UNINIT`
#3 [mir_promoted] processing `UNINIT`
#4 [mir_borrowck] borrow-checking `UNINIT`
#5 [analysis] running analysis passes on this crate
end of query stack

[jyn514]

This isn't really a bug, it's just that it has bad diagnostics because it uses rustc_layout_scalar_valid_range_start, which is a perma-unstable attribute. I would recommend against reporting bugs that need rustc_* attributes unless they cause unsoundness.

[jyn514]

MCVE:

#![feature(rustc_attrs)]
#[rustc_layout_scalar_valid_range_start(A)]
struct T {}
const C: T = T {};

[chengniansun]

@jyn514

Should I exclude all test programs that have a line starting with #[rustc_?

Thanks.

[jyn514]

I don't personally feel comfortable setting a policy that we'll never fix ICEs with rustc_ attributes, but they are definitely less likely to be bugs than other ICEs.

a line starting with #[rustc_

Note that this isn't sufficient to catch programs that have an attribute, you can have arbitrary macros that play with conditional compilation, like cfg_if. Catching #[rustc_ and #[cfg_attr(xxx, rustc_ will probably hit the common cases, though (you may want to also include inner attributes).