transmute const generic parameter

[DutchGhost]

I know you should never ever ever do this, yet it causes an ICE.
Also note I didn't turn on the #![feature(const_transmute)] feature

#![feature(const_generics)]

use std::mem::transmute;

struct Bug<const N: fn(usize)>;

fn main() {
    let x = Bug::<{
        unsafe { transmute(|x: u8| {}) }
        
    }>;
}

Backtrace:

Standard Error

   Compiling playground v0.0.1 (/playground)
warning: the feature `const_generics` is incomplete and may cause the compiler to crash
 --> src/main.rs:1:12
  |
1 | #![feature(const_generics)]
  |            ^^^^^^^^^^^^^^

error[E0658]: The use of std::mem::transmute() is gated in constants
 --> src/main.rs:9:18
  |
9 |         unsafe { transmute(|x: u8| {}) }
  |                  ^^^^^^^^^^^^^^^^^^^^^
  |
  = note: for more information, see https://github.com/rust-lang/rust/issues/53605
  = help: add #![feature(const_transmute)] to the crate attributes to enable

thread 'rustc' panicked at 'Size mismatch when transmuting!
src: OpTy {
    op: Immediate(
        Scalar(
            <ZST>,
        ),
    ),
    layout: TyLayout {
        ty: [closure@src/main.rs:9:28: 9:38],
        details: LayoutDetails {
            variants: Single {
                index: 0,
            },
            fields: Arbitrary {
                offsets: [],
                memory_index: [],
            },
            abi: Aggregate {
                sized: true,
            },
            align: AbiAndPrefAlign {
                abi: Align {
                    pow2: 0,
                },
                pref: Align {
                    pow2: 3,
                },
            },
            size: Size {
                raw: 0,
            },
        },
    },
}
dest: PlaceTy {
    place: Ptr(
        MemPlace {
            ptr: AllocId(0).0x0,
            align: Align {
                pow2: 3,
            },
            meta: None,
        },
    ),
    layout: TyLayout {
        ty: fn(usize),
        details: LayoutDetails {
            variants: Single {
                index: 0,
            },
            fields: Union(
                0,
            ),
            abi: Scalar(
                Scalar {
                    value: Pointer,
                    valid_range: 1..=18446744073709551615,
                },
            ),
            align: AbiAndPrefAlign {
                abi: Align {
                    pow2: 3,
                },
                pref: Align {
                    pow2: 3,
                },
            },
            size: Size {
                raw: 8,
            },
        },
    },
}', src/librustc_mir/interpret/place.rs:865:9
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.25/src/backtrace/libunwind.rs:97
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.25/src/backtrace/mod.rs:66
   2: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:47
   3: std::sys_common::backtrace::print
             at src/libstd/sys_common/backtrace.rs:36
   4: std::panicking::default_hook::{{closure}}
             at src/libstd/panicking.rs:197
   5: std::panicking::default_hook
             at src/libstd/panicking.rs:211
   6: rustc::util::common::panic_hook
   7: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:478
   8: std::panicking::continue_panic_fmt
             at src/libstd/panicking.rs:381
   9: std::panicking::begin_panic_fmt
             at src/libstd/panicking.rs:336
  10: rustc_mir::interpret::place::<impl rustc_mir::interpret::eval_context::InterpretCx<M>>::copy_op_transmute
  11: rustc_mir::interpret::intrinsics::<impl rustc_mir::interpret::eval_context::InterpretCx<M>>::emulate_intrinsic
  12: <rustc_mir::const_eval::CompileTimeInterpreter as rustc_mir::interpret::machine::Machine>::call_intrinsic
  13: rustc_mir::interpret::terminator::<impl rustc_mir::interpret::eval_context::InterpretCx<M>>::eval_fn_call
  14: rustc_mir::interpret::step::<impl rustc_mir::interpret::eval_context::InterpretCx<M>>::run
  15: rustc_mir::const_eval::eval_body_using_ecx
  16: rustc_mir::const_eval::const_eval_raw_provider
  17: rustc::ty::query::__query_compute::const_eval_raw
  18: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::const_eval_raw>::compute
  19: rustc::dep_graph::graph::DepGraph::with_task_impl
  20: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  21: rustc_mir::const_eval::const_eval_provider
  22: rustc::ty::query::__query_compute::const_eval
  23: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::const_eval>::compute
  24: rustc::dep_graph::graph::DepGraph::with_task_impl
  25: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  26: <rustc::traits::project::AssocTypeNormalizer as rustc::ty::fold::TypeFolder>::fold_const
  27: <smallvec::SmallVec<A> as core::iter::traits::collect::FromIterator<<A as smallvec::Array>::Item>>::from_iter
  28: rustc::ty::fold::TypeFoldable::fold_with
  29: rustc::ty::structural_impls::<impl rustc::ty::fold::TypeFoldable for &rustc::ty::TyS>::super_fold_with
  30: <rustc::traits::project::AssocTypeNormalizer as rustc::ty::fold::TypeFolder>::fold_ty
  31: rustc::traits::project::normalize
  32: rustc_typeck::check::FnCtxt::instantiate_value_path
  33: rustc_typeck::check::FnCtxt::check_expr_kind
  34: rustc_typeck::check::FnCtxt::check_expr_with_expectation_and_needs
  35: rustc_typeck::check::FnCtxt::check_decl_initializer
  36: rustc_typeck::check::FnCtxt::check_decl_local
  37: rustc_typeck::check::FnCtxt::check_stmt
  38: rustc_typeck::check::FnCtxt::check_block_with_expected
  39: rustc_typeck::check::FnCtxt::check_expr_kind
  40: rustc_typeck::check::FnCtxt::check_expr_with_expectation_and_needs
  41: rustc_typeck::check::FnCtxt::check_return_expr
  42: rustc_typeck::check::check_fn
  43: rustc::ty::context::GlobalCtxt::enter_local
  44: rustc_typeck::check::typeck_tables_of
  45: rustc::ty::query::__query_compute::typeck_tables_of
  46: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::typeck_tables_of>::compute
  47: rustc::dep_graph::graph::DepGraph::with_task_impl
  48: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  49: rustc::ty::<impl rustc::ty::context::TyCtxt>::par_body_owners
  50: rustc_typeck::check::typeck_item_bodies
  51: rustc::ty::query::__query_compute::typeck_item_bodies
  52: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::typeck_item_bodies>::compute
  53: rustc::dep_graph::graph::DepGraph::with_task_impl
  54: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  55: rustc::util::common::time
  56: rustc_typeck::check_crate
  57: rustc_interface::passes::analysis
  58: rustc::ty::query::__query_compute::analysis
  59: rustc::dep_graph::graph::DepGraph::with_task_impl
  60: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  61: rustc::ty::context::tls::enter_global
  62: rustc_interface::passes::BoxedGlobalCtxt::access::{{closure}}
  63: rustc_interface::passes::create_global_ctxt::{{closure}}
  64: rustc_interface::interface::run_compiler_in_existing_thread_pool
  65: std::thread::local::LocalKey<T>::with
  66: scoped_tls::ScopedKey<T>::set
  67: syntax::with_globals
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
query stack during panic:
#0 [const_eval_raw] const-evaluating `main::{{constant}}#0`
#1 [const_eval] const-evaluating + checking `main::{{constant}}#0`
#2 [typeck_tables_of] processing `main`
#3 [typeck_item_bodies] type-checking all item bodies
#4 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to previous error

For more information about this error, try `rustc --explain E0658`.

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/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.37.0-nightly (03ee55bb1 2019-06-01) running on x86_64-unknown-linux-gnu

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

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

error: Could not compile `playground`.

To learn more, run the command again with --verbose.

[JohnTitor]

This is still ICE but needs #![feature(const_compare_raw_pointers)] feature gate. playground

[JohnTitor]

It might be fixed (via glacier), could someone confirm?

[Alexendoo]

Fixed by #67192