ICE with std::mem::size_of with `repr(packed)` plus associated type

[grind086]

The compiler panics when there's a std::mem::size_of call for a struct with repr(packed) that contains a matrix type from nalgebra. I'm fairly new to rust and I'm not sure how to isolate what within the nalgebra crate might be causing this.

src/main.rs:

use nalgebra as na;

#[repr(packed)]
struct Foo(na::Vector3<f32>);

fn main() {
    std::mem::size_of::<Foo>();
}

Cargo.toml

[package]
name = "test"
version = "0.1.0"
authors = ["Robert Grindeland <rgrindeland@gmail.com>"]
edition = "2018"

[dependencies]
nalgebra = "0.16.13"

Result of RUST_BACKTRACE=1 cargo build --verbose

$ RUST_BACKTRACE=1 cargo build --verbose
       Fresh rand_core v0.4.0
       Fresh libm v0.1.2
       Fresh rawpointer v0.1.0
       Fresh rand_core v0.3.1
       Fresh num-traits v0.2.6
       Fresh winapi v0.3.6
       Fresh typenum v1.10.0
       Fresh matrixmultiply v0.1.15
       Fresh num-complex v0.2.1
       Fresh approx v0.3.1
       Fresh rand v0.5.6
       Fresh generic-array v0.11.1
       Fresh alga v0.7.2
       Fresh nalgebra v0.16.13
   Compiling test v0.1.0 (C:\Users\Rob\Documents\Programming\cpp\compiler-bug)
     Running `rustc --edition=2018 --crate-name test 'src\main.rs' --color always --crate-type bin --emit=dep-info,link -C debuginfo=2 -C metadata=9be42db9345f3907 -C extra-filename=-9be42db9345f3907 --out-dir 'C:\Users\Rob\Documents\Programming\cpp\compiler-bug\target\debug\deps' -C 'incremental=C:\Users\Rob\Documents\Programming\cpp\compiler-bug\target\debug\incremental' -L 'dependency=C:\Users\Rob\Documents\Programming\cpp\compiler-bug\target\debug\deps' --extern 'nalgebra=C:\Users\Rob\Documents\Programming\cpp\compiler-bug\target\debug\deps\libnalgebra-4080678600ea4cae.rlib'`
error: internal compiler error: librustc_typeck\check\wfcheck.rs:261: inference variables in nalgebra::base::matrix::Matrix<f32, nalgebra::base::dimension::U3, nalgebra::base::dimension::U1, nalgebra::base::array_storage::ArrayStorage<_, _, _>>
 --> src\main.rs:4:1
  |
4 | struct Foo(na::Vector3<f32>);
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

thread 'main' panicked at 'Box<Any>', librustc_errors\lib.rs:538:9
stack backtrace:
   0: <std::sync::mpsc::select::Select as core::fmt::Debug>::fmt
   1: std::path::<impl core::convert::From<std::path::PathBuf> for std::ffi::os_str::OsString>::from
   2: std::panicking::take_hook
   3: std::panicking::take_hook
   4: <rustc::ty::sty::Binder<rustc::ty::ProjectionPredicate<'tcx>> as rustc::ty::ToPredicate<'tcx>>::to_predicate
   5: std::panicking::rust_panic_with_hook
   6: rustc_typeck::collect::early_bound_lifetimes_from_generics
   7: rustc_typeck::collect::early_bound_lifetimes_from_generics
   8: <rustc_typeck::outlives::explicit::ExplicitPredicatesMap<'tcx> as core::fmt::Debug>::fmt
   9: <rustc_typeck::outlives::explicit::ExplicitPredicatesMap<'tcx> as core::fmt::Debug>::fmt
  10: <rustc_typeck::outlives::explicit::ExplicitPredicatesMap<'tcx> as core::fmt::Debug>::fmt
  11: <rustc_typeck::outlives::explicit::ExplicitPredicatesMap<'tcx> as core::fmt::Debug>::fmt
  12: <rustc_typeck::outlives::explicit::ExplicitPredicatesMap<'tcx> as core::fmt::Debug>::fmt
  13: <rustc_typeck::outlives::explicit::ExplicitPredicatesMap<'tcx> as core::fmt::Debug>::fmt
  14: <rustc_typeck::outlives::explicit::ExplicitPredicatesMap<'tcx> as core::fmt::Debug>::fmt
  15: <rustc_typeck::outlives::explicit::ExplicitPredicatesMap<'tcx> as core::fmt::Debug>::fmt
  16: <rustc_typeck::check::method::probe::ProbeScope as core::fmt::Debug>::fmt
  17: <rustc_typeck::check::upvar::InferBorrowKind<'a, 'gcx, 'tcx> as rustc::middle::expr_use_visitor::Delegate<'tcx>>::mutate
  18: <rustc::traits::query::outlives_bounds::OutlivesBound<'a> as rustc::ty::context::Lift<'tcx>>::lift_to_tcx
  19: rustc::ty::context::tls::track_diagnostic
  20: rustc::dep_graph::graph::DepGraph::assert_ignored
  21: rustc::ty::adjustment::<impl core::convert::From<rustc::ty::adjustment::AutoBorrowMutability> for rustc::hir::Mutability>::from
  22: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::try_print_query_stack
  23: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::try_print_query_stack
  24: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::try_print_query_stack
  25: <rustc_typeck::outlives::implicit_infer::IgnoreSelfTy as core::fmt::Debug>::fmt
  26: <rustc_typeck::check::regionck::RegionCtxt<'a, 'gcx, 'tcx> as rustc::hir::intravisit::Visitor<'gcx>>::nested_visit_map
  27: rustc_typeck::check_crate
  28: <humantime::date::Error as std::error::Error>::cause
  29: <rustc_driver::pretty::NoAnn<'hir> as rustc_driver::pretty::HirPrinterSupport<'hir>>::sess
  30: <humantime::date::Error as std::error::Error>::cause
  31: rustc_driver::driver::compile_input
  32: rustc_driver::run_compiler
  33: <rustc_driver::profile::trace::Query as core::fmt::Debug>::fmt
  34: rustc_driver::run_compiler
  35: <rustc_driver::profile::trace::Query as core::fmt::Debug>::fmt
  36: _rust_maybe_catch_panic
  37: <unknown>
  38: rustc_driver::main
  39: <unknown>
  40: std::panicking::update_panic_count
  41: _rust_maybe_catch_panic
  42: std::rt::lang_start_internal
  43: <unknown>
  44: <unknown>
  45: BaseThreadInitThunk
  46: RtlUserThreadStart
query stack during panic:
#0 [check_item_well_formed] processing `Foo`
end of query stack
error: aborting due to previous error


note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.31.1 (b6c32da9b 2018-12-18) running on x86_64-pc-windows-msvc

note: compiler flags: -C debuginfo=2 -C incremental --crate-type bin

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

error: Could not compile `test`.

Caused by:
  process didn't exit successfully: `rustc --edition=2018 --crate-name test 'src\main.rs' --color always --crate-type bin --emit=dep-info,link -C debuginfo=2 -C metadata=9be42db9345f3907 -C extra-filename=-9be42db9345f3907 --out-dir 'C:\Users\Rob\Documents\Programming\cpp\compiler-bug\target\debug\deps' -C 'incremental=C:\Users\Rob\Documents\Programming\cpp\compiler-bug\target\debug\incremental' -L 'dependency=C:\Users\Rob\Documents\Programming\cpp\compiler-bug\target\debug\deps' --extern 'nalgebra=C:\Users\Rob\Documents\Programming\cpp\compiler-bug\target\debug\deps\libnalgebra-4080678600ea4cae.rlib'` (exit code: 101)

[memoryruins]

Slightly minimized (this can be reduced much more); the ICE in the following also occurs with std::mem::size_of commented out

https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=2d169e6074e39a9cc9057ac3f5562f2c

use std::any::Any;
use std::fmt::Debug;
use std::marker::PhantomData;

#[repr(packed)]
struct Foo(Vector3<f32>);

fn main() {
    // std::mem::size_of::<Foo>();
}

#[repr(C)]
#[derive(Clone, Copy)]
pub struct Matrix<N: Scalar, R: Dim, C: Dim, S> {
    pub data: S,
    _phantoms: PhantomData<(N, R, C)>,
}

type MatrixMN<N, R, C> = Matrix<N, R, C, Owned<N, R, C>>;
type VectorN<N, D> = MatrixMN<N, D, U1>;
type Vector3<N> = VectorN<N, U3>;

pub trait Dim: Any + Debug + Copy + PartialEq + Send + Sync {}

#[derive(Debug, Copy, Clone, Hash, PartialEq, Eq)]
pub struct U1;
impl Dim for U1 {}

#[derive(Debug, Copy, Clone, Hash, PartialEq, Eq)]
pub struct U3;
impl Dim for U3 {}

pub trait Scalar: Copy + PartialEq + Debug + Any {}
impl<T: Copy + PartialEq + Debug + Any> Scalar for T {}

pub unsafe trait Storage<N: Scalar, R: Dim, C: Dim = U1>: Debug + Sized {
    type RStride: Dim;
    type CStride: Dim;
}
pub unsafe trait StorageMut<N: Scalar, R: Dim, C: Dim = U1>: Storage<N, R, C> {}

pub unsafe trait ContiguousStorage<N: Scalar, R: Dim, C: Dim = U1>:
    Storage<N, R, C>
{
}

pub unsafe trait ContiguousStorageMut<N: Scalar, R: Dim, C: Dim = U1>:
    ContiguousStorage<N, R, C> + StorageMut<N, R, C>
{
}

pub trait Allocator<N: Scalar, R: Dim, C: Dim = U1>: Any + Sized {
    type Buffer: ContiguousStorageMut<N, R, C> + Clone;
}

pub struct DefaultAllocator;
pub type Owned<N, R, C = U1> = <DefaultAllocator as Allocator<N, R, C>>::Buffer;

error: internal compiler error: src/librustc_typeck/check/wfcheck.rs:255: inference variables in Matrix<f32, U3, U1, _>
 --> src/main.rs:6:1
  |
6 | struct Foo(Vector3<f32>);
  | ^^^^^^^^^^^^^^^^^^^^^^^^^

thread 'rustc' panicked at 'Box<Any>', src/librustc_errors/lib.rs:543:9
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:39
   1: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:70
   2: std::panicking::default_hook::{{closure}}
             at src/libstd/sys_common/backtrace.rs:58
             at src/libstd/panicking.rs:200
   3: std::panicking::default_hook
             at src/libstd/panicking.rs:215
   4: rustc::util::common::panic_hook
   5: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:482
   6: std::panicking::begin_panic
   7: rustc_errors::Handler::span_bug
   8: rustc::util::bug::opt_span_bug_fmt::{{closure}}
   9: rustc::ty::context::tls::with_opt::{{closure}}
  10: rustc::ty::context::tls::with_context_opt
  11: rustc::ty::context::tls::with_opt
  12: rustc::util::bug::opt_span_bug_fmt
  13: rustc::util::bug::span_bug_fmt
  14: rustc_typeck::check::wfcheck::check_type_defn::{{closure}}::{{closure}}::{{closure}}
  15: rustc::ty::context::GlobalCtxt::enter_local
  16: rustc_typeck::check::wfcheck::check_item_well_formed
  17: rustc::ty::query::__query_compute::check_item_well_formed
  18: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors<'tcx> for rustc::ty::query::queries::check_item_well_formed<'tcx>>::compute
  19: rustc::dep_graph::graph::DepGraph::with_task_impl
  20: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::try_get_with
  21: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::ensure_query
  22: rustc::hir::Crate::visit_all_item_likes
  23: rustc::util::common::time
  24: rustc_typeck::check_crate
  25: <std::thread::local::LocalKey<T>>::with
  26: rustc::ty::context::TyCtxt::create_and_enter
  27: rustc_driver::driver::compile_input
  28: rustc_driver::run_compiler_with_pool
  29: <scoped_tls::ScopedKey<T>>::set
  30: rustc_driver::run_compiler
  31: <scoped_tls::ScopedKey<T>>::set
query stack during panic:
#0 [check_item_well_formed] processing `Foo`
end of query stack
error: aborting due to previous error

note: rustc 1.34.0-nightly (f6fac4225 2019-02-03) running on x86_64-unknown-linux-gnu

note: compiler flags: -C codegen-units=1 -C debuginfo=2 --crate-type bin

rustc 1.34.0-nightly (f6fac4225 2019-02-03)

[memoryruins]

Minimized further:
https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=e1c3725bd288e50631a4cf100538469f

pub struct Matrix<S> {}
pub struct DefaultAllocator;

pub trait Allocator {
    type Buffer;
}

#[repr(packed)]
struct Foo(Matrix<<DefaultAllocator as Allocator>::Buffer>);

[hellow554]

Even more:

#[repr(packed)]
pub struct Foo(<Vec<u32> as IntoIterator>::Item);

The ICE does not happen without the #[repr(packed)] attribute (also neat: this code would compile without warning when used as a testcase)

[hellow554]

Also note, that this "never worked" (I went back to nightly-2018-03-01, and even there it panics).

[pnkfelix]

triage. Marking P-high mostly because 1. it is an ICE and 2. I want to ensure it is at the front of the T-compiler queue for next week's meeting.

[pnkfelix]

(also neat: this code would compile without warning when used as a testcase)

@hellow554 can you clarify what you meant by this parenthetical? Are you saying if I add #[test] somewhere to the file it compiles without any error or warning?

[pnkfelix]

triage: assigning to self.