Adding functions through crate level syntax extensions crashes compiler

[Rantanen]

Having a MultiDecorator push function items on an attribute defined on the crate level (#![...) will result in the compiler crashing if these functions are called from the code.

#![decorator]  // Changing this to #[decorator] prevents the crash.

fn main() {
    decorated_method();  // Commenting out this line prevents the crash.
}

Full reproduction case is at https://github.com/Rantanen/com-export-rs/tree/issue
intercom-issue.zip

Use cargo run --example example

Meta

rustc --version --verbose:
rustc 1.22.0-nightly (f6d7514 2017-10-17)
binary: rustc
commit-hash: f6d7514
commit-date: 2017-10-17
host: x86_64-pc-windows-msvc
release: 1.22.0-nightly
LLVM version: 4.0

Backtrace:

thread 'rustc' panicked at 'Box<Any>', src\librustc_errors\lib.rs:492:8
stack backtrace:
   0: _rdl_shrink_in_place
   1: std::panicking::Location::column
   2: std::panicking::Location::column
   3: std::panicking::rust_panic_with_hook
   4: <unknown>
   5: rustc_errors::Handler::bug
   6: rustc::session::bug_fmt
   7: rustc::session::bug_fmt
   8: rustc::session::bug_fmt
   9: rustc::hir::map::Map::read
  10: rustc::hir::map::Map::span
  11: rustc::ty::maps::<impl rustc::ty::maps::queries::def_span<'tcx>>::ensure
  12: rustc::ty::maps::<impl rustc::ty::maps::queries::def_span<'tcx>>::try_get
  13: rustc::ty::maps::TyCtxtAt::def_span
  14: rustc::ty::maps::<impl rustc::ty::maps::queries::lookup_deprecation_entry<'tcx>>::try_get
  15: rustc::ty::maps::TyCtxtAt::lookup_deprecation_entry
  16: rustc::middle::stability::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::check_stability
  17: <rustc::middle::stability::Checker<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_path

Edit: I removed the branch repro branch from the repository. It was causing problems with Codecov, which figured it was the default branch. Zip file of the repro case attached instead.

[TimNN]

I'm not sure this is a bug or not -- I don't think plugins were intended to be used like this. But maybe the compiler should report a better error in that case.

[Rantanen]

Yeah, the "emit crate-level code" use case can be handled by macros so getting this to work isn't on that high priority I guess.

But it would be nice if rustc didn't panic on it. :)

[Rantanen]

Closing in favor of proc macros over syntax extensions. There are still ICEs with proc macros in the crate-level case, but those are described in #41430 in more detail.