unexpected compiler panic in cast.rs

[avadacatavra]

Not totally sure why this happened. When I forgot an extern crate the compiler panicked with the following 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/blob/master/CONTRIBUTING.md#bug-reports

note: rustc 1.23.0-nightly (e21df8020 2017-11-13) running on x86_64-apple-darwin

note: run with `RUST_BACKTRACE=1` for a backtrace

thread 'rustc' panicked at 'explicit panic', src/librustc_typeck/check/cast.rs:110:17
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
stack backtrace:
   0: std::sys::imp::backtrace::tracing::imp::unwind_backtrace
   1: std::sys_common::backtrace::_print
   2: std::panicking::default_hook::{{closure}}
   3: std::panicking::default_hook
   4: std::panicking::rust_panic_with_hook
   5: std::panicking::begin_panic
   6: rustc_typeck::check::cast::<impl rustc_typeck::check::FnCtxt<'a, 'gcx, 'tcx>>::pointer_kind
   7: rustc_typeck::check::cast::<impl rustc_typeck::check::FnCtxt<'a, 'gcx, 'tcx>>::pointer_kind
   8: rustc_typeck::check::cast::<impl rustc_typeck::check::FnCtxt<'a, 'gcx, 'tcx>>::pointer_kind
   9: rustc_typeck::check::cast::CastCheck::check
  10: rustc_typeck::check::FnCtxt::check_casts
  11: <std::thread::local::LocalKey<T>>::with
  12: rustc::ty::context::GlobalCtxt::enter_local
  13: _ZN12rustc_typeck5check16typeck_tables_of17h2991cb3aa7f93926E.llvm.5BE90B30
  14: rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_tables_of<'tcx>>::compute_result
  15: _ZN5rustc9dep_graph5graph8DepGraph14with_task_impl17hdc0895b856803ac5E.llvm.E968ED05
  16: rustc_errors::Handler::track_diagnostics
  17: rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::cycle_check
  18: rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_tables_of<'tcx>>::force
  19: rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_tables_of<'tcx>>::try_get
  20: rustc::ty::maps::TyCtxtAt::typeck_tables_of
  21: rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_tables_of<'tcx>>::ensure
  22: rustc::session::Session::track_errors
  23: _ZN12rustc_typeck5check18typeck_item_bodies17h619021d8d31ccdb0E.llvm.5BE90B30
  24: rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_item_bodies<'tcx>>::compute_result
  25: _ZN5rustc9dep_graph5graph8DepGraph14with_task_impl17h09adb0a33cf7a8d7E.llvm.E968ED05
  26: rustc_errors::Handler::track_diagnostics
  27: rustc::ty::maps::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::cycle_check
  28: rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_item_bodies<'tcx>>::force
  29: rustc::ty::maps::<impl rustc::ty::maps::queries::typeck_item_bodies<'tcx>>::try_get
  30: rustc::ty::maps::TyCtxtAt::typeck_item_bodies
  31: rustc::ty::maps::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::typeck_item_bodies
  32: rustc_typeck::check_crate
  33: <std::thread::local::LocalKey<T>>::with
  34: <std::thread::local::LocalKey<T>>::with
  35: rustc::ty::context::TyCtxt::create_and_enter
  36: rustc_driver::driver::compile_input
  37: rustc_driver::run_compiler

[kennytm]

Hi do you have the code that caused this bug? Thanks!

[avadacatavra]

Instead of using std::cell::{Ref, RefCell, RefMut};, I switched to use accountable_refcell::{RefCell, Ref, RefMut}; in https://dxr.mozilla.org/servo/source/components/script/dom/bindings/cell.rs#7

accountable_refcell was in the Cargo.toml, but I'd forgotten to put an extern crate in lib.rs. Then I ran ./mach check (equiv to cargo check)

[kennytm]

@avadacatavra I just noticed that the nightly version in the report is rustc 1.23.0-nightly (e21df8020 2017-11-13). Could you update the nightly to the current one (1.24.0-nightly (73bca2b9f 2017-11-28)) and try again?

[arielb1]

This reproduces the ICE (on beta but not on stable)

use std::fmt;
fn main() {
    let foo: *mut (fmt::Display,) = 0 as *mut _;
}

Now the question is whether @avadacatavra had a different reproduction

[Deewiant]

Bisecting using @arielb1's latest example points to #44295 as the cause. (Not sure exactly which commit — the three commits preceding 1e9e319 don't compile and I didn't feel like sorting it out.)

[arielb1]

So I found the "real" example:

use std::fmt;
struct Lorem {
    ipsum: Ipsum
}
fn main() {
    let foo: *mut Lorem = 0 as *mut _;
}