cargo-clippy panics on MaybeUninit::<AtomicPtr<T>>::uninit().assume_init()

[yukiiiteru]

Code

Here is the MVP code, there must be MaybeUninit::uninit().assume_init() for AtomicPtr with generic type T:

use std::{mem::MaybeUninit, sync::atomic::AtomicPtr};

struct Foo<T> {
    ptr: AtomicPtr<T>,
}

impl<T> Foo<T> {
    unsafe fn foo() {
        let _: Self = MaybeUninit::uninit().assume_init();
    }
}

cargo build works, but cargo clippy crashes.

Meta

rustc --version --verbose:

stable:

rustc 1.80.0 (051478957 2024-07-21)
binary: rustc
commit-hash: 051478957371ee0084a7c0913941d2a8c4757bb9
commit-date: 2024-07-21
host: x86_64-unknown-linux-gnu
release: 1.80.0
LLVM version: 18.1.7

nightly:

rustc 1.82.0-nightly (8e86c9567 2024-08-01)
binary: rustc
commit-hash: 8e86c9567154dc5a9ada15ab196d23eae2bd7d89
commit-date: 2024-08-01
host: x86_64-unknown-linux-gnu
release: 1.82.0-nightly
LLVM version: 19.1.0

Both stable and nightly builds crash.

Error output

error: internal compiler error: /rustc/8e86c9567154dc5a9ada15ab196d23eae2bd7d89/compiler/rustc_middle/src/ty/layout.rs:961:21: failed to get layout for `std::sync::atomic::AtomicPtr<T>`: Unknown(Alias(Projection, AliasTy { args: [T/#0], def_id: DefId(2:2227 ~ core[5b06]::ptr::metadata::Pointee::Metadata), .. })),
                                despite it being a field (#0) of an existing layout: TyAndLayout {
                                    ty: Foo<T>,
                                    layout: Layout {
                                        size: Size(8 bytes),
                                        align: AbiAndPrefAlign {
                                            abi: Align(8 bytes),
                                            pref: Align(8 bytes),
                                        },
                                        abi: Aggregate {
                                            sized: true,
                                        },
                                        fields: Arbitrary {
                                            offsets: [
                                                Size(0 bytes),
                                            ],
                                            memory_index: [
                                                0,
                                            ],
                                        },
                                        largest_niche: None,
                                        variants: Single {
                                            index: 0,
                                        },
                                        max_repr_align: Some(
                                            Align(8 bytes),
                                        ),
                                        unadjusted_abi_align: Align(8 bytes),
                                    },
                                }

Backtrace

stable:

$ RUST_BACKTRACE=1 cargo clippy
    Checking ice-reproduce v0.1.0 (/tmp/ice-reproduce)
warning: struct `Foo` is never constructed
 --> src/lib.rs:3:8
  |
3 | struct Foo<T> {
  |        ^^^
  |
  = note: `#[warn(dead_code)]` on by default

warning: associated function `foo` is never used
 --> src/lib.rs:8:15
  |
7 | impl<T> Foo<T> {
  | -------------- associated function in this implementation
8 |     unsafe fn foo() {
  |               ^^^

error: internal compiler error: /rustc/8e86c9567154dc5a9ada15ab196d23eae2bd7d89/compiler/rustc_middle/src/ty/layout.rs:961:21: failed to get layout for `std::sync::atomic::AtomicPtr<T>`: Unknown(Alias(Projection, AliasTy { args: [T/#0], def_id: DefId(2:2227 ~ core[5b06]::ptr::metadata::Pointee::Metadata), .. })),
                                despite it being a field (#0) of an existing layout: TyAndLayout {
                                    ty: Foo<T>,
                                    layout: Layout {
                                        size: Size(8 bytes),
                                        align: AbiAndPrefAlign {
                                            abi: Align(8 bytes),
                                            pref: Align(8 bytes),
                                        },
                                        abi: Aggregate {
                                            sized: true,
                                        },
                                        fields: Arbitrary {
                                            offsets: [
                                                Size(0 bytes),
                                            ],
                                            memory_index: [
                                                0,
                                            ],
                                        },
                                        largest_niche: None,
                                        variants: Single {
                                            index: 0,
                                        },
                                        max_repr_align: Some(
                                            Align(8 bytes),
                                        ),
                                        unadjusted_abi_align: Align(8 bytes),
                                    },
                                }

thread 'rustc' panicked at /rustc/8e86c9567154dc5a9ada15ab196d23eae2bd7d89/compiler/rustc_middle/src/ty/layout.rs:961:21:
Box<dyn Any>
stack backtrace:
   0: std::panicking::begin_panic::<rustc_errors::ExplicitBug>
   1: <rustc_errors::diagnostic::BugAbort as rustc_errors::diagnostic::EmissionGuarantee>::emit_producing_guarantee
   2: rustc_middle::util::bug::opt_span_bug_fmt::<rustc_span::span_encoding::Span>::{closure#0}
   3: rustc_middle::ty::context::tls::with_opt::<rustc_middle::util::bug::opt_span_bug_fmt<rustc_span::span_encoding::Span>::{closure#0}, !>::{closure#0}
   4: rustc_middle::ty::context::tls::with_context_opt::<rustc_middle::ty::context::tls::with_opt<rustc_middle::util::bug::opt_span_bug_fmt<rustc_span::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
   5: rustc_middle::util::bug::bug_fmt
   6: <rustc_const_eval::interpret::eval_context::InterpCx<rustc_const_eval::const_eval::machine::CompileTimeMachine>>::project_field::<rustc_const_eval::interpret::operand::OpTy>
   7: <rustc_const_eval::interpret::validity::ValidityVisitor<rustc_const_eval::const_eval::machine::CompileTimeMachine> as rustc_const_eval::interpret::visitor::ValueVisitor<rustc_const_eval::const_eval::machine::CompileTimeMachine>>::visit_value
   8: <rustc_const_eval::interpret::eval_context::InterpCx<rustc_const_eval::const_eval::machine::CompileTimeMachine>>::validate_operand_internal
   9: rustc_const_eval::util::check_validity_requirement::check_validity_requirement
  10: <rustc_const_eval::provide::{closure#2} as core::ops::function::FnOnce<(rustc_middle::ty::context::TyCtxt, (rustc_middle::ty::layout::ValidityRequirement, rustc_middle::ty::ParamEnvAnd<rustc_middle::ty::Ty>))>>::call_once
      [... omitted 3 frames ...]
  11: clippy_utils::ty::is_uninit_value_valid_for_ty
  12: clippy_lints::methods::uninit_assumed_init::check
  13: <clippy_lints::methods::Methods>::check_methods
  14: <clippy_lints::methods::Methods as rustc_lint::passes::LateLintPass>::check_expr
  15: <rustc_lint::late::LateContextAndPass<rustc_lint::late::RuntimeCombinedLateLintPass> as rustc_hir::intravisit::Visitor>::visit_expr::{closure#0}::{closure#0}
  16: <rustc_lint::late::LateContextAndPass<rustc_lint::late::RuntimeCombinedLateLintPass> as rustc_hir::intravisit::Visitor>::visit_expr
  17: rustc_hir::intravisit::walk_block::<rustc_lint::late::LateContextAndPass<rustc_lint::late::RuntimeCombinedLateLintPass>>
  18: <rustc_lint::late::LateContextAndPass<rustc_lint::late::RuntimeCombinedLateLintPass> as rustc_hir::intravisit::Visitor>::visit_block
  19: <rustc_lint::late::LateContextAndPass<rustc_lint::late::RuntimeCombinedLateLintPass> as rustc_hir::intravisit::Visitor>::visit_expr::{closure#0}::{closure#0}
  20: <rustc_lint::late::LateContextAndPass<rustc_lint::late::RuntimeCombinedLateLintPass> as rustc_hir::intravisit::Visitor>::visit_expr
  21: <rustc_lint::late::LateContextAndPass<rustc_lint::late::RuntimeCombinedLateLintPass> as rustc_hir::intravisit::Visitor>::visit_nested_body
  22: <rustc_lint::late::LateContextAndPass<rustc_lint::late::RuntimeCombinedLateLintPass> as rustc_hir::intravisit::Visitor>::visit_fn
  23: <rustc_lint::late::LateContextAndPass<rustc_lint::late::RuntimeCombinedLateLintPass> as rustc_hir::intravisit::Visitor>::visit_nested_item
  24: rustc_lint::late::check_crate::{closure#0}
  25: rustc_lint::late::check_crate
  26: rustc_interface::passes::analysis
      [... omitted 1 frame ...]
  27: rustc_interface::interface::run_compiler::<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

note: we would appreciate a bug report: https://github.com/rust-lang/rust-clippy/issues/new?template=ice.yml

note: please make sure that you have updated to the latest nightly

note: please attach the file at `/tmp/ice-reproduce/rustc-ice-2024-08-02T14_18_52-3442737.txt` to your bug report

note: compiler flags: --crate-type lib -C embed-bitcode=no -C debuginfo=2 -C incremental=[REDACTED] -C target-feature=+aes,+avx2,+bmi1,+bmi2,+f16c,+fma,+fxsr,+lzcnt,+movbe,+pclmulqdq,+popcnt,+rdrand,+rdseed,+xsave,+xsaveopt -C force-frame-pointers=yes

note: some of the compiler flags provided by cargo are hidden

query stack during panic:
#0 [check_validity_requirement] checking validity requirement for `Foo<T>`: allows being left uninitialized
#1 [analysis] running analysis passes on this crate
end of query stack
note: Clippy version: clippy 0.1.82 (8e86c95 2024-08-01)

warning: the type `Foo<T>` does not permit being left uninitialized
 --> src/lib.rs:9:23
  |
9 |         let _: Self = MaybeUninit::uninit().assume_init();
  |                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |                       |
  |                       this code causes undefined behavior when executed
  |                       help: use `MaybeUninit<T>` instead, and only call `assume_init` after initialization is done
  |
note: raw pointers must be initialized (in this struct field)
 --> src/lib.rs:4:5
  |
4 |     ptr: AtomicPtr<T>,
  |     ^^^^^^^^^^^^^^^^^
  = note: `#[warn(invalid_value)]` on by default

warning: `ice-reproduce` (lib) generated 3 warnings
error: could not compile `ice-reproduce` (lib); 3 warnings emitted

nightly has the same messages.

[ChrisDenton]

Clippy shouldn't panic here but do note that MaybeUninit::uninit().assume_init() is documented as causing immediate undefined behaviour.

[y21]

This looks very similar to #119620, probably the same underlying issue that's causing the ICE here?

[yukiiiteru]

Clippy shouldn't panic here but do note that MaybeUninit::uninit().assume_init() is documented as causing immediate undefined behaviour.

Yes it's really an UB, but it's not a reason to panic.

[Noratrieb]

yes, this is a duplicate of #119620
closing as such, thank you for the report!