ICE that can only be reproduced on playbot/play.rust-lang.org: casting a shared reference to a `*const` to a `*mut _` (lack of type required)

[bstrie]

Test case, that mysteriously passes on my machine but fails on the playpen:

fn main() {
    &2 as *const i32 as *mut _;
}

Playpen output:

<anon>:2:5: 2:31 error: internal compiler error: cat_expr Errd
<anon>:2     &2 as *const i32 as *mut _;
             ^~~~~~~~~~~~~~~~~~~~~~~~~~
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 'Box<Any>', /home/rustbuild/src/rust-buildbot/slave/beta-dist-rustc-linux/build/src/libsyntax/diagnostic.rs:149


playpen: application terminated with error code 101
Program ended.

Local output:

ice.rs:2:5: 2:31 error: cannot determine a type for this expression: unconstrained type [E0101]
ice.rs:2     &2 as *const i32 as *mut _;
             ^~~~~~~~~~~~~~~~~~~~~~~~~~
error: aborting due to previous error

Very strange...

[lilyball]

Seems like a Beta vs Nightly difference. Switching to the nightly for playpen yields

<anon>:2:5: 2:31 error: cannot determine a type for this expression: unconstrained type [E0101]
<anon>:2     &2 as *const i32 as *mut _;
             ^~~~~~~~~~~~~~~~~~~~~~~~~~

[pnkfelix]

yeah this is probably one of the cases that was "resolved" by #24367 . ("Resolved" is in quotes because the team would prefer to fix the issues that lead us to call cat_expr when it might return Err.)

[pnkfelix]

I closed this since the issue is resolved on nightly and the team had already decided not to backport the "fix" to the beta channel.