ICE when non-const in const path.

This is that backtrace and error.

ico@arch ted $ cargo run
   Compiling ted v0.1.0 (file:///home/ico/code/projects/ted)
src/text/buffer.rs:112:21: 112:27 error: paths in constants may only refer to constants or functions [E0014]
src/text/buffer.rs:112             0.0 ... vwidth => {
                                           ^~~~~~
src/text/buffer.rs:112:21: 112:27 help: run `rustc --explain E0014` to see a detailed explanation
src/text/buffer.rs:112:21: 112:27 error: non-constant path in constant expr
src/text/buffer.rs:112             0.0 ... vwidth => {
                                           ^~~~~~
src/text/buffer.rs:112:13: 112:20 error: internal compiler error: literals of different types in range pat
src/text/buffer.rs:112             0.0 ... vwidth => {
                                   ^~~~~~~
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
thread 'rustc' panicked at 'Box<Any>', ../src/libsyntax/diagnostic.rs:176

stack backtrace:
   1:     0x7f461dc9b679 - sys::backtrace::write::h8f163fbc2fd53e94Gds
   2:     0x7f461dca3506 - panicking::on_panic::hf28d92e1ddd2bb33rex
   3:     0x7f461dc694ee - rt::unwind::begin_unwind_inner::hba29b41ea2e4f2655Gw
   4:     0x7f461ac6de17 - rt::unwind::begin_unwind::h12470989743939357431
   5:     0x7f461ac6ddd6 - diagnostic::SpanHandler::span_bug::hee88dc31e7766ce0kZA
   6:     0x7f461bb52d93 - session::Session::span_bug::he4c27021eec2e8b8W7v
   7:     0x7f461bc5698e - middle::check_const::CheckCrateVisitor<'a, 'tcx>.Visitor<'v>::visit_pat::h6fd474360a009684h2f
   8:     0x7f461bc5d8fe - visit::walk_arm::h14700536703337769097
   9:     0x7f461bc5d719 - visit::walk_expr::h10555032929647284522
  10:     0x7f461bc554f0 - middle::check_const::CheckCrateVisitor<'a, 'tcx>.Visitor<'v>::visit_expr::hd39087c11f22e55el6f
  11:     0x7f461bc572ba - middle::check_const::CheckCrateVisitor<'a, 'tcx>.Visitor<'v>::visit_block::hc9ec746ad3afb9d783f
  12:     0x7f461bc56009 - middle::check_const::CheckCrateVisitor<'a, 'tcx>::fn_like::closure.86088
  13:     0x7f461bc55c54 - middle::check_const::CheckCrateVisitor<'a, 'tcx>::fn_like::he12f169b1eb8f048AMf
  14:     0x7f461bc5b1ea - visit::walk_impl_item::h13192287562712281624
  15:     0x7f461bc5acd0 - visit::walk_item::h2458628646849006222
  16:     0x7f461bc5a4f0 - middle::check_const::CheckCrateVisitor<'a, 'tcx>.Visitor<'v>::visit_item::hee874e109ff405c7NWf
  17:     0x7f461bc5a8df - visit::walk_item::h2458628646849006222
  18:     0x7f461bc5a4f0 - middle::check_const::CheckCrateVisitor<'a, 'tcx>.Visitor<'v>::visit_item::hee874e109ff405c7NWf
  19:     0x7f461bc5a8df - visit::walk_item::h2458628646849006222
  20:     0x7f461bc5a4f0 - middle::check_const::CheckCrateVisitor<'a, 'tcx>.Visitor<'v>::visit_item::hee874e109ff405c7NWf
  21:     0x7f461bc6319a - middle::check_const::check_crate::h8c2477442470bbbdxDg
  22:     0x7f461e1e80e0 - driver::phase_3_run_analysis_passes::closure.20587
  23:     0x7f461e1c6e95 - middle::ty::ctxt<'tcx>::create_and_enter::h9762542764631600212
  24:     0x7f461e1c1ffd - driver::phase_3_run_analysis_passes::h5985136415815979015
  25:     0x7f461e1a5716 - driver::compile_input::hcbc3a92ec764e7e5Tba
  26:     0x7f461e31038b - run_compiler::h0a02618e9f046bf8Obc
  27:     0x7f461e30dc57 - boxed::F.FnBox<A>::call_box::h16881755907780588363
  28:     0x7f461e30d6c4 - rt::unwind::try::try_fn::h16221945257817858538
  29:     0x7f461dca30a8 - __rust_try
  30:     0x7f461dc8f902 - rt::unwind::try::inner_try::h9ca0fee771d29e74YCw
  31:     0x7f461e30d858 - boxed::F.FnBox<A>::call_box::h16992707776166869464
  32:     0x7f461dca24f3 - sys::thread::Thread::new::thread_start::hda9462d1945ff67eLMv
  33:     0x7f46178a74a3 - start_thread
  34:     0x7f461d92d12c - clone
  35:                0x0 - <unknown>

Could not compile `ted`.

To learn more, run the command again with --verbose.
ico@arch ted $

This is the code that caused it.

fn next_letter_position(&self, x_index: f32, y_index: f32, width: f32) -> (f32, f32) {
    let vwidth = &self.viewport.x / 2.0;

    match x_index * width {
        0.0 ... vwidth => {
            (x_index + 1.0, y_index)
        },
        _ => (0.0, y_index - 1.0)
    }
}

rustc version

 rustc 1.4.0-nightly (10d69db0a 2015-08-23)

[alexispurslane]

I managed to reproduce this bug, and found it can be avoided by making vwidth constant.

[alexispurslane]

It looks like rust throws an ICE when it can't compare values in a range, here:

...
                match const_eval::compare_lit_exprs(self.tcx, start, end) {
                    Some(Ordering::Less) |
                    Some(Ordering::Equal) => {}
                    Some(Ordering::Greater) => {
                        span_err!(self.tcx.sess, start.span, E0030,
                            "lower range bound must be less than or equal to upper");
                    }
                    None => {
                        self.tcx.sess.span_bug(
                            start.span, "literals of different types in range pat");
                    }
                }
...

Edit: This is in librustc/middle/check_const.rs, lines 372-383

[alexispurslane]

Maybe self.tcx.sess.span_bug should be changed to span_err! to make it a non-ICE. If I do, what E00 should it be? E0014?

[arielb1]

@ChristopherDumas

An error message is already issued. It should just ignore it.

[alexispurslane]

@arielb1 I'm not sure what you mean. It looks to me like span_bug throws an ICE, and span_err! just issues a compile warning/error.

[arielb1]

@ChristopherDumas

Right, but global_expr already emitted an error (paths in constants may only refer to constants or functions). You don't want to emit another one.

[alexispurslane]

Ok i get it!

[alexispurslane]

It turns out that the error is already caught in compare_lit_exprs, so visit_pat should ignore the error, and let compare_lit_exprs handle it. The reason for two errors is that there are multiple things wrong with @ivegotasthma's code.

[oli-obk]

this doesn't ice anymore