ICE on nightly 2017-11-07: casting *const i64 to *mut _

[jeehoonkang]

• meta

  $ rustc --version
  rustc 1.23.0-nightly (ee2286149 2017-11-07)
  
  $ uname -a
  Darwin Jeehoon-Kangs-MacBook-Pro.local 16.7.0 Darwin Kernel Version 16.7.0: Thu Jun 15 17:36:27 PDT 2017; root:xnu-3789.70.16~2/RELEASE_X86_64 x86_64
  

• minimal example: https://play.rust-lang.org/?gist=231bf59b18642fcaba9a939dd43c41d8&version=nightly

  use std::ptr;
  
  fn main() {
      let p1: *const i64 = ptr::null();
      let p2 = p1 as *mut _;
  }

• error message (from playground)

     Compiling playground v0.0.1 (file:///playground)
  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 (ee2286149 2017-11-07) running on x86_64-unknown-linux-gnu
  
  thread 'rustc' panicked at 'explicit panic', /checkout/src/librustc_typeck/check/cast.rs:108:17
  note: Run with `RUST_BACKTRACE=1` for a backtrace.
  
  error: Could not compile `playground`.
  
  To learn more, run the command again with --verbose.
  

[est31]

bisect-rust says the regression is in commit dce604a PR #44295

cc @plietar @arielb1

[zmt00]

The example on the playground now just reports an error instead of producing an ICE on stable and nightly, which I believe is working as intended.

   Compiling playground v0.0.1 (file:///playground)
error[E0641]: cannot cast to a pointer of an unknown kind
 --> src/main.rs:5:14
  |
5 |     let p2 = p1 as *mut _;
  |              ^^^^^^------
  |                    |
  |                    help: consider giving more type information
  |
  = note: The type information given here is insufficient to check whether the pointer cast is valid

error: aborting due to previous error

For more information about this error, try `rustc --explain E0641`.
error: Could not compile `playground`.

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

[jeehoonkang]

Thanks!!

[est31]

Does this need a test? @cramertj