Panic on Option::unwrap inside rustc_typeck::check::compare_method::compare_const_impl

[Ruin0x11]

I got an ICE after adding #![feature(associated_consts)] to a project and migrating to nightly. Would appreciate help.

   Compiling sabi v0.1.0 (file:///home/nuko/build/sabi)
     Running `rustc --crate-name sabi src/main.rs --crate-type bin --emit=dep-info,link -C debuginfo=2 -C metadata=8ef730904cdb3202 -C extra-filename=-8ef730904cdb3202 --out-dir /home/nuko/build/sabi/target/debug/deps -L dependency=/home/nuko/build/sabi/target/debug/deps --extern lazy_static=/home/nuko/build/sabi/target/debug/deps/liblazy_static-18005fa1be5dd889.rlib --extern rustbox=/home/nuko/build/sabi/target/debug/deps/librustbox-0ce884825441c60e.rlib --extern chrono=/home/nuko/build/sabi/target/debug/deps/libchrono-6725d8b05e3d1a1e.rlib --extern enum_derive=/home/nuko/build/sabi/target/debug/deps/libenum_derive-571a57db87053f20.rlib --extern macro_attr=/home/nuko/build/sabi/target/debug/deps/libmacro_attr-8f0b61e973dcd6c1.rlib --extern backtrace=/home/nuko/build/sabi/target/debug/deps/libbacktrace-db0734c9c79848f2.rlib --extern goap=/home/nuko/build/sabi/target/debug/deps/libgoap-cae2f3d8a34a9aef.rlib --extern env_logger=/home/nuko/build/sabi/target/debug/deps/libenv_logger-ce278d65fff484a8.rlib --extern infinigen=/home/nuko/build/sabi/target/debug/deps/libinfinigen-95df6657b2a24fa0.rlib --extern serde=/home/nuko/build/sabi/target/debug/deps/libserde-46dd15ab79d4d223.rlib --extern slog=/home/nuko/build/sabi/target/debug/deps/libslog-eea2cd42d168e09d.rlib --extern slog_stream=/home/nuko/build/sabi/target/debug/deps/libslog_stream-738219c3754c3ec3.rlib --extern calx_ecs=/home/nuko/build/sabi/target/debug/deps/libcalx_ecs-c3b37e6a0ec71fa3.rlib --extern tcod=/home/nuko/build/sabi/target/debug/deps/libtcod-fa9483bd403fbbc0.rlib --extern toml=/home/nuko/build/sabi/target/debug/deps/libtoml-fb537ab82d6cf526.rlib --extern bitflags=/home/nuko/build/sabi/target/debug/deps/libbitflags-40c9799a6d297c75.rlib --extern uuid=/home/nuko/build/sabi/target/debug/deps/libuuid-9c058fc6aef3689f.rlib --extern rand=/home/nuko/build/sabi/target/debug/deps/librand-76456d761c2cb637.rlib --extern serde_derive=/home/nuko/build/sabi/target/debug/deps/libserde_derive-583ac15462b70281.so -L /home/nuko/build/sabi/target/debug/build/termbox-sys-679ef25ef47d21c5/out/lib -L native=/home/nuko/build/sabi/target/debug/build/backtrace-sys-1b1714f3e656f8c7/out/.libs -L native=/home/nuko/build/sabi/target/debug/build/miniz-sys-07cc64aa136ffbd3/out -L native=/home/nuko/build/sabi/target/debug/build/tcod-sys-7ff280fd359ac283/out -L native=/usr/lib -L native=/usr/lib -L native=/usr/lib -L /home/nuko/build/sabi/target/debug/build/tcod-sys-7ff280fd359ac283/out`
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: run with `RUST_BACKTRACE=1` for a backtrace

thread 'rustc' panicked at 'called `Option::unwrap()` on a `None` value', /checkout/src/libcore/option.rs:329
stack backtrace:
   0: std::sys::imp::backtrace::tracing::imp::unwind_backtrace
             at /checkout/src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: std::sys_common::backtrace::_print
             at /checkout/src/libstd/sys_common/backtrace.rs:71
   2: std::panicking::default_hook::{{closure}}
             at /checkout/src/libstd/sys_common/backtrace.rs:60
             at /checkout/src/libstd/panicking.rs:355
   3: std::panicking::default_hook
             at /checkout/src/libstd/panicking.rs:365
   4: std::panicking::rust_panic_with_hook
             at /checkout/src/libstd/panicking.rs:549
   5: std::panicking::begin_panic
             at /checkout/src/libstd/panicking.rs:511
   6: std::panicking::begin_panic_fmt
             at /checkout/src/libstd/panicking.rs:495
   7: rust_begin_unwind
             at /checkout/src/libstd/panicking.rs:471
   8: core::panicking::panic_fmt
             at /checkout/src/libcore/panicking.rs:69
   9: core::panicking::panic
             at /checkout/src/libcore/panicking.rs:49
  10: rustc_typeck::check::compare_method::compare_const_impl
  11: rustc_typeck::check::check_impl_items_against_trait
  12: rustc_typeck::check::check_item_type
  13: rustc_typeck::check::check_item_types
  14: rustc_typeck::check_crate
  15: rustc_driver::driver::phase_3_run_analysis_passes::{{closure}}
  16: rustc_driver::driver::phase_3_run_analysis_passes
  17: rustc_driver::driver::compile_input
  18: rustc_driver::run_compiler
  19: std::panicking::try::do_call
  20: __rust_maybe_catch_panic
             at /checkout/src/libpanic_unwind/lib.rs:98
  21: <F as alloc::boxed::FnBox<A>>::call_box
  22: std::sys::imp::thread::Thread::new::thread_start
             at /checkout/src/liballoc/boxed.rs:650
             at /checkout/src/libstd/sys_common/thread.rs:21
             at /checkout/src/libstd/sys/unix/thread.rs:84
  23: start_thread
  24: clone

$ rustc --version
rustc 1.18.0-nightly (2b4c91158 2017-04-25)

This might be the call to unwrap that panics.

[Ruin0x11]

Also, the state of the code I was working on was such that I was implementing a trait with provided methods, but accidentally implementing over the provided methods and not providing all the required methods.

[Ruin0x11]

Ok, the error was due to having the incorrect type on an associated constant:

// In library
pub trait ManagedChunk: Serialize + Deserialize {
    const SECTOR_SIZE: usize = 4096;

    const REGION_WIDTH: i32 = 16;
}

// ...

// In binary project
impl ManagedChunk for SerialChunk {
    const SECTOR_SIZE: u32 = 4096;

    const REGION_WIDTH: u32 = 16;
}

Fixing that makes the compiler panic go away.

But this example errors correctly on playground (nightly/debug):

#![feature(associated_consts)]

trait MyTrait: Clone {
    const MY_CONST: usize = 4096;
    const MY_OTHER_CONST: i32 = 16;
}

#[derive(Clone)]
struct Dude {
    
}

impl MyTrait for Dude {
    const MY_CONST: u32 = 4096;
    const MY_OTHER_CONST: u32 = 16;
}

fn main() {
    println!("{}", Dude::MY_CONST);
    println!("{}", Dude::MY_OTHER_CONST);
}

Output:

rustc 1.18.0-nightly (63c77214c 2017-04-24)
error[E0326]: implemented const `MY_CONST` has an incompatible type for trait
  --> <anon>:14:21
   |
4  |     const MY_CONST: usize = 4096;
   |                     ----- type in trait
...
14 |     const MY_CONST: u32 = 4096;
   |                     ^^^ expected usize, found u32

error[E0326]: implemented const `MY_OTHER_CONST` has an incompatible type for trait
  --> <anon>:15:27
   |
5  |     const MY_OTHER_CONST: i32 = 16;
   |                           --- type in trait
...
15 |     const MY_OTHER_CONST: u32 = 16;
   |                           ^^^ expected i32, found u32

error: aborting due to 2 previous errors