ICE: not allowed to compare these idents

[alexcrichton]

#![feature(macro_rules)]
macro_rules! input_state(( $ ex : expr ) => ( { byte_var ! new } ))
mod tests {
    fn Or_NoMatch() { (0.apply & input_state!("a").is_none) }
}

error: internal compiler error: unexpected failure
note: the compiler hit an unexpected failure path. this is a bug.
note: we would appreciate a bug report: http://static.rust-lang.org/doc/master/complement-bugreport.html
note: run with `RUST_BACKTRACE=1` for a backtrace
task 'rustc' failed at 'not allowed to compare these idents: &ast::Ident{name: 59u32, ctxt: 19u32}, &ast::Ident{name: 0u32, ctxt: 0u32}. Probably related to issue #6993', /Users/rustbuild/src/rust-buildbot/slave/nightly-mac/build/src/libsyntax/ast.rs:68
stack backtrace:
   1:        0x10c08d175 - rt::backtrace::imp::write::h32a901d3233d0bdeE1F::v0.11.pre
   2:        0x10bffa26e - rt::unwind::begin_unwind_inner::h52cff5c2686d96bdIBF::v0.11.pre
   3:        0x10bff8d97 - rt::unwind::begin_unwind_fmt::hdb4700a1dfec81b3SAF::v0.11.pre
   4:        0x10b78236c - parse::parser::Parser<'a>::parse_stmt::he515390da1e27d25hND::v0.11.pre
   5:        0x10b78aa63 - parse::parser::Parser<'a>::parse_block_tail_::h2f51e97e8d565df8BYD::v0.11.pre
   6:        0x10b77118e - parse::parser::Parser<'a>::parse_bottom_expr::h4988a2bceb66a1beDnC::v0.11.pre
   7:        0x10b779bf7 - parse::parser::Parser<'a>::parse_dot_or_call_expr::h6392555e78fda78fREC::v0.11.pre
   8:        0x10b77d49c - parse::parser::Parser<'a>::parse_prefix_expr::h96ba6280abc96291BWC::v0.11.pre
   9:        0x10b77e277 - parse::parser::Parser<'a>::parse_binops::hac39d19878dc62fdk3C::v0.11.pre
  10:        0x10b77ebdd - parse::parser::Parser<'a>::parse_assign_expr::hdab4d37969fe0c21I6C::v0.11.pre
  11:        0x10b8c6bc4 - ext::tt::macro_rules::ParserAnyMacro<'a>.MacResult::make_expr::h1faeaf54f539b3b50xZ::v0.11.pre
  12:        0x10b80b86c - ext::expand::expand_expr::h25209d1545858b2aCXR::v0.11.pre
  13:        0x10b812560 - ext::expand::MacroExpander<'a, 'b>.Folder::fold_expr::hea28abcb466d80caeOS::v0.11.pre
  14:        0x10b8144ce - fold::noop_fold_expr::h2300662414445522736::v0.11.pre
  15:        0x10b80a9b5 - ext::expand::expand_expr::h25209d1545858b2aCXR::v0.11.pre
  16:        0x10b812560 - ext::expand::MacroExpander<'a, 'b>.Folder::fold_expr::hea28abcb466d80caeOS::v0.11.pre
  17:        0x10b813d69 - fold::noop_fold_expr::h2300662414445522736::v0.11.pre
  18:        0x10b80a9b5 - ext::expand::expand_expr::h25209d1545858b2aCXR::v0.11.pre
  19:        0x10b812560 - ext::expand::MacroExpander<'a, 'b>.Folder::fold_expr::hea28abcb466d80caeOS::v0.11.pre
  20:        0x10b8138d2 - fold::noop_fold_expr::h2300662414445522736::v0.11.pre
  21:        0x10b80a9b5 - ext::expand::expand_expr::h25209d1545858b2aCXR::v0.11.pre
  22:        0x10b81f387 - ext::expand::expand_block_elts::ha491c8964ad51f24bKS::v0.11.pre
  23:        0x10b84b63d - ext::expand::expand_block::h75f7ec8aef4d573avJS::v0.11.pre
  24:        0x10b81baa4 - ext::expand::MacroExpander<'a, 'b>.Folder::fold_block::h486720cd6877aaf1nPS::v0.11.pre
  25:        0x10b8246d1 - fold::noop_fold_item::h11788381394573765963::v0.11.pre
  26:        0x10b81ff52 - ext::expand::expand_item::h27c9057d930da5ae8aS::v0.11.pre
  27:        0x10b8274f3 - ext::expand::MacroExpander<'a, 'b>.Folder::fold_item::h9c937407fdde583evOS::v0.11.pre
  28:        0x10b82748c - fold::noop_fold_mod::closure.25703
  29:        0x10b827052 - iter::Iterator::collect::h12687141241212812692::v0.11.pre
  30:        0x10b8268b8 - fold::Folder::fold_mod::h16438108110856807369::v0.11.pre
  31:        0x10b82478f - fold::noop_fold_item::h11788381394573765963::v0.11.pre
  32:        0x10b81fe5d - ext::expand::expand_item::h27c9057d930da5ae8aS::v0.11.pre
  33:        0x10b8274f3 - ext::expand::MacroExpander<'a, 'b>.Folder::fold_item::h9c937407fdde583evOS::v0.11.pre
  34:        0x10b82748c - fold::noop_fold_mod::closure.25703
  35:        0x10b827052 - iter::Iterator::collect::h12687141241212812692::v0.11.pre
  36:        0x10b8268b8 - fold::Folder::fold_mod::h16438108110856807369::v0.11.pre
  37:        0x10b84c0c6 - ext::expand::expand_crate::h15557a7b962e1dbb9PS::v0.11.pre
  38:        0x109acd6a7 - driver::driver::phase_2_configure_and_expand::closure.89779
  39:        0x109accb29 - util::common::time::h1661115251862896670::v0.11.pre
  40:        0x109acaa94 - driver::driver::phase_2_configure_and_expand::hb3d8bf5849d428a2V9h::v0.11.pre
  41:        0x109b0e076 - driver::driver::compile_input::h3c36b14f5a6b267dgEi::v0.11.pre
  42:        0x109b35671 - run_compiler::h9fb8ea47126bd32bsaq::v0.11.pre
  43:        0x109b4d1ed - main_args::closure.93974
  44:        0x109b4b962 - monitor::closure.93852
  45:        0x109b464bb - task::TaskBuilder::try::closure.93618
  46:        0x1092afb8c - task::spawn_opts::closure.7397
  47:        0x10c0847d8 - rt::task::Task::run::closure.28413
  48:        0x10c0a570c - rust_try
  49:        0x10c084657 - rt::task::Task::run::h6132448717581d41XqD::v0.11.pre
  50:        0x1092afa0f - task::spawn_opts::closure.7369
  51:        0x10c08bad6 - rt::thread::thread_start::h63737de03963ea2288D::v0.11.pre
  52:     0x7fff92309899 - _pthread_body
  53:     0x7fff9230972a - _pthread_struct_init

[lilyball]

I think this is a dupe of #10536.

The backtrace is a bit different than the original case for #10536, but both end up ICE'ing inside parse_stmt for the same reason, and there's already a minimal reproduction case in #10536 for this exact same variant.