impossible case reached: bad combination of types for cast

[mhobbs-8B]

Running Arch Linux: 3.17.6-1-ARCH #1 SMP PREEMPT Sun Dec 7 23:43:32 UTC 2014 x86_64 GNU/Linux

rustc 1.0.0-nightly (f4f10db 2015-01-17 20:31:08 +0000)
binary: rustc
commit-hash: f4f10db
commit-date: 2015-01-17 20:31:08 +0000
host: x86_64-unknown-linux-gnu
release: 1.0.0-nightly

Here's the line that caused the error:
pub static mut SOCKS_HOST: *const str = 0 as *const str;

backtrace:

thread 'rustc' panicked at 'Box<Any>', /home/rustbuild/src/rust-buildbot/slave/nightly-dist-rustc-linux/build/src/libsyntax/diagnostic.rs:126

stack backtrace:
   1:     0x7f81445c3c90 - sys::backtrace::write::hda88ebe91818f572tXt
   2:     0x7f81445e5b90 - failure::on_fail::h9fbfe25f5b38e775qeA
   3:     0x7f8144554300 - rt::unwind::begin_unwind_inner::h1bd92865247a942cjTz
   4:     0x7f813efd7770 - rt::unwind::begin_unwind::h15336451338054780329
   5:     0x7f813efd7700 - diagnostic::SpanHandler::span_bug::h110bf60630d186b1VoF
   6:     0x7f814293e690 - session::Session::impossible_case::h7839f1024fe36b1etFp
   7:     0x7f8143d5eb50 - trans::consts::const_expr_unadjusted::he1dcbfb2818dd7e8Gfo
   8:     0x7f8143d5cdb0 - trans::consts::const_expr::h734b9de8ebda8b92N4n
   9:     0x7f8143c977b0 - trans::base::get_item_val::h8df99413e1d50374a3u
  10:     0x7f8143d64450 - trans::consts::trans_static::hfe38a6a23470d6e4UJo
  11:     0x7f8143c952c0 - trans::base::trans_item::h25a1b35201e5520bCyu
  12:     0x7f8143d7d320 - trans::base::trans_mod::h63dc8a5716cd3e9eeEu
  13:     0x7f8143c952c0 - trans::base::trans_item::h25a1b35201e5520bCyu
  14:     0x7f8143d804d0 - trans::base::trans_crate::hcee70ebbe1e36918juv
  15:     0x7f8144b26a70 - driver::phase_4_translate_to_llvm::h1d3249612b78766ewOa
  16:     0x7f8144b06960 - driver::compile_input::h9092b12341e3a857Cba
  17:     0x7f8144bc8340 - run_compiler::h62323e6edb706ae8nac
  18:     0x7f8144bc6ab0 - thunk::F.Invoke<A, R>::invoke::h12018745279237426453
  19:     0x7f8144bc5a10 - rt::unwind::try::try_fn::h1504517046915204584
  20:     0x7f814464cc00 - rust_try_inner
  21:     0x7f814464cbf0 - rust_try
  22:     0x7f8144bc5cc0 - thunk::F.Invoke<A, R>::invoke::h3360625291245025634
  23:     0x7f81445d37f0 - sys::thread::thread_start::h4faa993964f784ad5Nw
  24:     0x7f813e7f3250 - start_thread
  25:     0x7f8144205219 - clone
  26:                0x0 - <unknown>

[nathantypanski]

This is falling through the match expression on /src/librustc_trans/trans/consts.rs#L518-L521

&'static str -> *const str panics also:

ice.rs:1:35: 1:51 error: internal compiler error: impossible case reached: bad combination of types for cast
ice.rs:1 pub static mut fail: *const str = "" as *const str;
                                           ^~~~~~~~~~~~~~~~
note: the compiler unexpectedly panicked. this is a bug.
note: we would appreciate a bug report: http://doc.rust-lang.org/complement-bugreport.html
note: run with `RUST_BACKTRACE=1` for a backtrace
thread 'rustc' panicked at 'Box<Any>', /home/nathan/prj/rust/rust/src/libsyntax/diagnostic.rs:126

stack backtrace:
   1:     0x7ffbb1e686d0 - sys::backtrace::write::hfb11ddfd0e7f0658eRt
   2:     0x7ffbb1e8a5a0 - failure::on_fail::hbcb8cd329aec6ff6J4z
   3:     0x7ffbb1df8e20 - rt::unwind::begin_unwind_inner::haafd3e91071bc3e1XJz
   4:     0x7ffbaca18810 - rt::unwind::begin_unwind::h6185406380551317121
   5:     0x7ffbaca187a0 - diagnostic::SpanHandler::span_bug::h6c67dceaab6289dcEpF
   6:     0x7ffbb01eb3b0 - session::Session::impossible_case::h3d86ed69bec12c961fp
   7:     0x7ffbb16033e0 - trans::consts::const_expr_unadjusted::h7bbb3fd0d30587f7ado
   8:     0x7ffbb1601640 - trans::consts::const_expr::h62680ecd661789d2h2n
   9:     0x7ffbb153bfe0 - trans::base::get_item_val::heeb56e6127c59fe8IYu
  10:     0x7ffbb1608ce0 - trans::consts::trans_static::h24dedd3ba4c51141fHo
  11:     0x7ffbb1539af0 - trans::base::trans_item::h386d32b9df74fe59iuu
  12:     0x7ffbb1624ce0 - trans::base::trans_crate::h777b6fde95f212b0Lpv
  13:     0x7ffbb23d2d40 - driver::phase_4_translate_to_llvm::he23925e56602061eTNa
  14:     0x7ffbb23b2c30 - driver::compile_input::hb4efdf66e0f650f5Cba
  15:     0x7ffbb247d9a0 - run_compiler::h9d3e14b442c4d365l9b
  16:     0x7ffbb247c110 - thunk::F.Invoke<A, R>::invoke::h14209112065483412921
  17:     0x7ffbb247b070 - rt::unwind::try::try_fn::h1021622462190646014
  18:     0x7ffbb1efa120 - rust_try_inner
  19:     0x7ffbb1efa110 - rust_try
  20:     0x7ffbb247b320 - thunk::F.Invoke<A, R>::invoke::h14035172896832106325
  21:     0x7ffbb1e78210 - sys::thread::thread_start::he2d36a2cbcaf629dzGw
  22:     0x7ffbac233250 - start_thread
  23:     0x7ffbb1aa9219 - clone
  24:                0x0 - <unknown>

I believe the case happening here is (expr::cast_integral, expr::cast_other), based on
a similar, but not quite equivalent, failure with the following code:

fn main() {
    let mut fail: *const str = 0 as *const str;
}

error: internal compiler error: translating unsupported cast: usize (cast_integral) -> *const str (cast_other)
note: the compiler unexpectedly panicked. this is a bug.
note: we would appreciate a bug report: http://doc.rust-lang.org/complement-bugreport.html
note: run with `RUST_BACKTRACE=1` for a backtrace
thread 'rustc' panicked at 'Box<Any>', /home/nathan/prj/rust/rust/src/libsyntax/diagnostic.rs:185

stack backtrace:
   1:     0x7f373294c6d0 - sys::backtrace::write::hfb11ddfd0e7f0658eRt
   2:     0x7f373296e5a0 - failure::on_fail::hbcb8cd329aec6ff6J4z
   3:     0x7f37328dce20 - rt::unwind::begin_unwind_inner::haafd3e91071bc3e1XJz
   4:     0x7f372d4fc810 - rt::unwind::begin_unwind::h6185406380551317121
   5:     0x7f372d4fd0b0 - diagnostic::Handler::bug::h22dd58059bfb9b94EvF
   6:     0x7f3730a00710 - session::Session::bug::ha3b9a2f7768518e0Ucp
   7:     0x7f373209a930 - trans::expr::trans_imm_cast::h6237da60fefe9c376ek
   8:     0x7f373207e5a0 - trans::expr::trans_unadjusted::he8968cac83a4541c4ii
   9:     0x7f3732037ed0 - trans::expr::trans::h8455960f4e8fd42dCBh
  10:     0x7f3732036d30 - trans::expr::trans_into::h83699b23dbd8bfcf8xh
  11:     0x7f37321378a0 - trans::_match::mk_binding_alloca::h10237289352598662242
  12:     0x7f37320363a0 - trans::base::init_local::h919eb93f221f2a7065s
  13:     0x7f3732037330 - trans::controlflow::trans_block::h2d166cd595ca56b6Z2d
  14:     0x7f3732101a70 - trans::base::trans_closure::h7bc248b8281c1222wWt
  15:     0x7f3732022930 - trans::base::trans_fn::h79df99adfc5fa22276t
  16:     0x7f373201daf0 - trans::base::trans_item::h386d32b9df74fe59iuu
  17:     0x7f3732108ce0 - trans::base::trans_crate::h777b6fde95f212b0Lpv
  18:     0x7f3732eb6d40 - driver::phase_4_translate_to_llvm::he23925e56602061eTNa
  19:     0x7f3732e96c30 - driver::compile_input::hb4efdf66e0f650f5Cba
  20:     0x7f3732f619a0 - run_compiler::h9d3e14b442c4d365l9b
  21:     0x7f3732f60110 - thunk::F.Invoke<A, R>::invoke::h14209112065483412921
  22:     0x7f3732f5f070 - rt::unwind::try::try_fn::h1021622462190646014
  23:     0x7f37329de120 - rust_try_inner
  24:     0x7f37329de110 - rust_try
  25:     0x7f3732f5f320 - thunk::F.Invoke<A, R>::invoke::h14035172896832106325
  26:     0x7f373295c210 - sys::thread::thread_start::he2d36a2cbcaf629dzGw
  27:     0x7f372cd17250 - start_thread
  28:     0x7f373258d219 - clone
  29:                0x0 - <unknown>

The above bugs out somewhere in src/librustc_trans/trans/expr.rs#L2047-L2061

Should either of these casts actually succeed?

[shepmaster]

Saw a similar case:

static mut static_trait: *mut (Trait + 'static) = 0 as *mut _;
pub trait Trait {}
pub fn main() {}

on rustc 1.0.0-dev (342ab53bf 2015-02-15 12:20:31 +0000)

[tamird]

Triage: still ICEs.

fn main() {
    let mut fail: *const str = 0 as *const str;
}

and

static mut static_trait: *mut (Trait + 'static) = 0 as *mut _;
pub trait Trait {}
pub fn main() {}