ICE when trying to use &impl in a binding

[smarnach]

This code results in an ICE on the playground:

#![feature(impl_trait_in_bindings)]

use std::ops::Add;

fn main() {
    let i: i32 = 0;
    let j: &impl Add = &i;
}

This may be a duplicate of #54600, but I can't really tell. Error message:

   Compiling playground v0.0.1 (/playground)
warning: unused variable: `j`
 --> src/main.rs:7:9
  |
7 |     let j: &impl Add = &i;
  |         ^ help: consider using `_j` instead
  |
  = note: #[warn(unused_variables)] on by default

error: internal compiler error: broken MIR in DefId(0/0:4 ~ playground[bf48]::main[0]) (_2 = &(*_3)): bad assignment (&impl std::ops::Add = &i32): NoSolution
 --> src/main.rs:7:24
  |
7 |     let j: &impl Add = &i;
  |                        ^^

thread 'main' panicked at 'no errors encountered even though `delay_span_bug` issued', librustc_errors/lib.rs:334:17
note: Run with `RUST_BACKTRACE=1` for a 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 1.31.0-nightly (8c4ad4e9e 2018-10-04) 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.

[estebank]

error: internal compiler error: broken MIR in DefId(0/0:4 ~ playground[bf48]::main[0]) (_2 = &(*_3)): bad assignment (&impl std::ops::Add = &i32): NoSolution
 --> src/main.rs:7:24
  |
7 |     let j: &impl Add = &i;
  |                        ^^

thread 'main' panicked at 'no errors encountered even though `delay_span_bug` issued', librustc_errors/lib.rs:334:17
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: std::sys_common::backtrace::print
             at libstd/sys_common/backtrace.rs:71
             at libstd/sys_common/backtrace.rs:59
   2: std::panicking::default_hook::{{closure}}
             at libstd/panicking.rs:211
   3: std::panicking::default_hook
             at libstd/panicking.rs:227
   4: rustc::util::common::panic_hook
   5: std::panicking::rust_panic_with_hook
             at libstd/panicking.rs:480
   6: std::panicking::begin_panic
   7: <rustc_errors::Handler as core::ops::drop::Drop>::drop
   8: core::ptr::drop_in_place
   9: core::ptr::drop_in_place
  10: core::ptr::drop_in_place
  11: syntax::with_globals
  12: __rust_maybe_catch_panic
             at libpanic_unwind/lib.rs:102
  13: rustc_driver::run
  14: rustc_driver::main
  15: std::rt::lang_start::{{closure}}
  16: std::panicking::try::do_call
             at libstd/rt.rs:59
             at libstd/panicking.rs:310
  17: __rust_maybe_catch_panic
             at libpanic_unwind/lib.rs:102
  18: std::rt::lang_start_internal
             at libstd/panicking.rs:289
             at libstd/panic.rs:392
             at libstd/rt.rs:58
  19: main
  20: __libc_start_main
  21: <unknown>
query stack during panic:
end of query stack

error: internal compiler error: unexpected panic

[varkor]

cc @alexreg

[alexreg]

Yeah, impl Trait in bindings is horribly broken, sorry. It’s just not implemented right, internally. I’ll be sure to add this as a test case when I get back to work on it next week or so. Thanks for the report though.