MIR-borrowck: ICE: this path should not cause illegal move

[arielb1]

MIR-borrowck: moves out of arrays and slices cause an ICE instead of a correct error. For example, this code (the compile-fail test E0508):

struct NonCopy;

fn main() {
    let array = [NonCopy; 1];
    let _value = array[0]; //~ ERROR E0508
}

Causes the following ICE with MIR borrowck:

error[E0508]: cannot move out of type `[NonCopy; 1]`, a non-copy array (Ast)
 --> e0509.rs:5:18
  |
5 |     let _value = array[0]; //~ ERROR E0508
  |                  ^^^^^^^^
  |                  |
  |                  cannot move out of here
  |                  help: consider using a reference instead: `&array[0]`

error: internal compiler error: rust://src/librustc_mir/util/borrowck_errors.rs:274: this path should not cause illegal move
 --> e0509.rs:5:18
  |
5 |     let _value = array[0]; //~ ERROR E0508
  |                  ^^^^^^^^

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-dev running on x86_64-unknown-linux-gnu

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

thread 'rustc' panicked at 'Box<Any>', rust://src/librustc_errors/lib.rs:450:8
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
             at rust://src/libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: std::sys_common::backtrace::_print
             at rust://src/libstd/sys_common/backtrace.rs:69
   2: std::panicking::default_hook::{{closure}}
             at rust://src/libstd/sys_common/backtrace.rs:58
             at rust://src/libstd/panicking.rs:381
   3: std::panicking::default_hook
             at rust://src/libstd/panicking.rs:391
   4: std::panicking::rust_panic_with_hook
             at rust://src/libstd/panicking.rs:577
   5: std::panicking::begin_panic
             at rust://src/libstd/panicking.rs:538
   6: rustc_errors::Handler::span_bug
             at ./<panic macros>:3
   7: rustc::session::opt_span_bug_fmt::{{closure}}
             at rust://src/librustc/session/mod.rs:980
   8: rustc::session::span_bug_fmt
             at rust://src/librustc/ty/context.rs:1538
             at rust://src/librustc/ty/context.rs:1527
             at rust://src/libstd/thread/local.rs:377
             at rust://src/libstd/thread/local.rs:288
             at rust://src/librustc/ty/context.rs:1523
             at rust://src/librustc/ty/context.rs:1538
             at rust://src/librustc/session/mod.rs:977
             at rust://src/librustc/session/mod.rs:970
   9: rustc_mir::util::borrowck_errors::BorrowckErrors::cannot_move_out_of_interior_noncopy
             at rust://src/librustc_mir/util/borrowck_errors.rs:274
  10: rustc_mir::borrow_check::mir_borrowck::{{closure}}
             at rust://src/librustc_mir/borrow_check.rs:83
  11: rustc_mir::borrow_check::mir_borrowck
             at rust://src/librustc/infer/mod.rs:375
             at rust://src/librustc/ty/context.rs:1511
             at rust://src/libstd/thread/local.rs:377
             at rust://src/libstd/thread/local.rs:288
             at rust://src/librustc/ty/context.rs:1508
             at rust://src/librustc/ty/context.rs:1319
             at rust://src/librustc/infer/mod.rs:375
             at rust://src/librustc_mir/borrow_check.rs:61
  12: rustc::dep_graph::graph::DepGraph::with_task_impl
             at rust://src/librustc/ty/maps/plumbing.rs:390
             at rust://src/librustc/dep_graph/graph.rs:287
  13: rustc::ty::maps::<impl rustc::ty::maps::queries::mir_borrowck<'tcx>>::force
             at rust://src/librustc/dep_graph/graph.rs:203
             at rust://src/librustc/ty/maps/plumbing.rs:442
             at rust://src/librustc_errors/lib.rs:566
             at rust://src/librustc/ty/maps/plumbing.rs:435
             at rust://src/librustc/ty/maps/plumbing.rs:130
             at rust://src/librustc/ty/maps/plumbing.rs:434
  14: rustc::ty::maps::<impl rustc::ty::maps::queries::mir_borrowck<'tcx>>::try_get
             at rust://src/librustc/ty/maps/plumbing.rs:313
             at rust://src/librustc/ty/maps/plumbing.rs:471
  15: rustc::ty::maps::TyCtxtAt::mir_borrowck
             at rust://src/librustc/ty/maps/plumbing.rs:510
  16: rustc::ty::maps::<impl rustc::ty::context::TyCtxt<'a, 'tcx, 'lcx>>::mir_borrowck
             at rust://src/librustc/ty/maps/plumbing.rs:503
  17: rustc_driver::driver::phase_3_run_analysis_passes::{{closure}}::{{closure}}
             at rust://src/librustc_driver/driver.rs:1095
  18: rustc::ty::context::TyCtxt::create_and_enter
             at rust://src/librustc/util/common.rs:120
             at rust://src/librustc_driver/driver.rs:1093
             at rust://src/librustc/ty/context.rs:1511
             at rust://src/libstd/thread/local.rs:377
             at rust://src/libstd/thread/local.rs:288
             at rust://src/librustc/ty/context.rs:1508
             at rust://src/librustc/ty/context.rs:1495
             at rust://src/libstd/thread/local.rs:377
             at rust://src/libstd/thread/local.rs:288
             at rust://src/librustc/ty/context.rs:1492
             at rust://src/librustc/ty/context.rs:1136
  19: rustc_driver::driver::compile_input
             at rust://src/librustc_driver/driver.rs:1041
             at rust://src/librustc_driver/driver.rs:210
  20: rustc_driver::run_compiler
             at rust://src/librustc_driver/lib.rs:252

It should be fixed to emit the same error as the AST.