ICE: With `writeln!` after recent changes in std::fmt

[japaric]

STR

use std::fmt::Show;
use std::io::PipeStream;

struct Program {
    stdin: PipeStream,
}

impl Program {
    fn send<T: Show>(&mut self, line: T) -> &mut Program {
        // OK
        //match writeln!(&mut self.stdin, "{}", line) {
        // ICE
        match writeln!(self.stdin, "{}", line) {
            Err(_) => panic!(),
            Ok(_) => self,
        }
    }
}

fn main() {}

Output

task 'rustc' panicked at 'index out of bounds: the len is 6 but the index is 6', /var/tmp/paludis/build/dev-lang-rust-scm/work/rust-scm/src/libsyntax/lib.rs:1

stack backtrace:
   1:     0x7f7ac0e18a30 - rt::backtrace::imp::write::h2b9052e6d9bc7115y9s
   2:     0x7f7ac0e1bbd0 - <unknown>
   3:     0x7f7ac15bdea0 - unwind::begin_unwind_inner::h045530faf4b26040nbd
   4:     0x7f7ac15bdb20 - unwind::begin_unwind_fmt::hbb3cb48652ded377y8c
   5:     0x7f7ac15bdae0 - rust_begin_unwind
   6:     0x7f7ac15fa590 - panicking::panic_fmt::hc3aa7deba1f6ed540Nl
   7:     0x7f7ac15ff980 - panicking::panic_bounds_check::h40d1ef7dd63df707yMl
   8:     0x7f7abec8bba0 - codemap::FileMap::get_line::haca5f2812f60e330m4E
   9:     0x7f7abecba5c0 - <unknown>
  10:     0x7f7abecb6fe0 - diagnostic::EmitterWriter.Emitter::emit::h8944016a574210b0lrG
  11:     0x7f7abecb5860 - diagnostic::Handler::emit::hef6d94e096dac3f1F8F
  12:     0x7f7abec88380 - diagnostic::SpanHandler::span_err::he4174115bd82cc5fEWF
  13:     0x7f7ac00875d0 - middle::typeck::infer::InferCtxt<'a, 'tcx>::type_error_message_str_with_expected::h0350e4ffa557951e6rF
  14:     0x7f7abffd1cc0 - middle::typeck::infer::InferCtxt<'a, 'tcx>::type_error_message::h216c2650f9e1a343qxF
  15:     0x7f7abffdb420 - <unknown>
  16:     0x7f7abffdb420 - <unknown>
  17:     0x7f7ac0011ca0 - middle::typeck::check::check_decl_local::hba8b231eaafb10e9vao
  18:     0x7f7ac0011e60 - middle::typeck::check::check_stmt::ha5de4679bb4bc747vco
  19:     0x7f7abff93bc0 - <unknown>
  20:     0x7f7abffdb420 - <unknown>
  21:     0x7f7abfec6f70 - middle::typeck::check::_match::check_match::h4e3330be3e1c359eyz8
  22:     0x7f7abffdb420 - <unknown>
  23:     0x7f7abff93bc0 - <unknown>
  24:     0x7f7abff6b9b0 - <unknown>
  25:     0x7f7abff904c0 - <unknown>
  26:     0x7f7abff96bd0 - <unknown>
  27:     0x7f7abff8c2b0 - middle::typeck::check::check_item::hd604129538ea4d11VQi
  28:     0x7f7abff90150 - middle::typeck::check::check_item_types::h1a3e4c15e3ead8aeXvi
  29:     0x7f7ac0333c60 - <unknown>
  30:     0x7f7ac0332e70 - middle::typeck::check_crate::he5192d314e6838dfhdM
  31:     0x7f7ac1ab8bf0 - driver::driver::phase_3_run_analysis_passes::he238813c217c3b94efS
  32:     0x7f7ac1aada10 - driver::driver::compile_input::h117f94c1b348a398YVR
  33:     0x7f7ac1b323d0 - <unknown>
  34:     0x7f7ac1b322c0 - <unknown>
  35:     0x7f7ac193ef30 - <unknown>
  36:     0x7f7ac193ed20 - <unknown>
  37:     0x7f7ac1e52b70 - <unknown>
  38:     0x7f7ac160cfe0 - <unknown>
  39:     0x7f7ac160cfd0 - rust_try
  40:     0x7f7ac15bb800 - unwind::try::h03ead95328113b2fIZc
  41:     0x7f7ac15bb690 - task::Task::run::hed7dc0cf620a0172y5b
  42:     0x7f7ac1e528b0 - <unknown>
  43:     0x7f7ac15bceb0 - <unknown>
  44:     0x7f7abc08a1d0 - start_thread
  45:     0x7f7ac12941b9 - clone
  46:                0x0 - <unknown>

Version

Equivalent code was compiling with:

rustc 0.13.0-nightly (e09d98603 2014-11-18 23:51:43 +0000)

But now it's ICEing on: 1d81776

I think #19040 may have introduced the ICE.

cc @alexcrichton

This is a dupe of #14091, closing.

The real error here is obscured by a well-known bug in codemap that causes diagnostics to blow up if they originate in code expanded from external macros. We really need to fix that one...