Compiler error on #[async_trait] when async-trait is not in Cargo.toml

[scull7]

I tried this code:

#[async_trait]
pub trait Thing {
    type Item;
    
    fn not_async(&self) -> String

    async fn get_thing(&self) -> anyhow::Result<Self::Item>;
}

I expected to see this happen:

I would expect the compiler to complain about the missing crate

Instead, this happened:

thread 'rustc' panicked at 'called `Option::unwrap()` on a `None` value', /rustc/d3fb005a39e62501b8b0b356166e515ae24e2e54/src/librustc_hir/definitions.rs:358:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

error: internal compiler error: unexpected panic

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

note: rustc 1.45.2 (d3fb005a3 2020-07-31) running on x86_64-apple-darwin

note: compiler flags: -C embed-bitcode=no -C debuginfo=2 -C incremental -C linker=clang --crate-type lib

note: some of the compiler flags provided by cargo are hidden

Meta

rustc --version --verbose:

rustc 1.45.2 (d3fb005a3 2020-07-31)
binary: rustc
commit-hash: d3fb005a39e62501b8b0b356166e515ae24e2e54
commit-date: 2020-07-31
host: x86_64-apple-darwin
release: 1.45.2
LLVM version: 10.0
<version>

Backtrace

thread 'rustc' panicked at 'called `Option::unwrap()` on a `None` value', /rustc/d3fb005a39e62501b8b0b356166e515ae24e2e54/src/librustc_hir/definitions.rs:358:9
stack backtrace:
   0: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
   1: core::fmt::write
   2: std::io::Write::write_fmt
   3: std::panicking::default_hook::{{closure}}
   4: std::panicking::default_hook
   5: rustc_driver::report_ice
   6: std::panicking::rust_panic_with_hook
   7: rust_begin_unwind
   8: core::panicking::panic_fmt
   9: core::panicking::panic
  10: rustc_middle::hir::map::Map::def_kind
  11: core::ops::function::FnOnce::call_once
  12: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  13: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  14: rustc_data_structures::stack::ensure_sufficient_stack
  15: rustc_query_system::query::plumbing::get_query_impl
  16: rustc_middle::ty::util::<impl rustc_middle::ty::context::TyCtxt>::closure_base_def_id
  17: rustc_typeck::collect::generics_of
  18: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::generics_of>::compute
  19: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  20: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  21: rustc_query_system::query::plumbing::get_query_impl
  22: rustc_query_system::query::plumbing::ensure_query_impl
  23: rustc_hir::intravisit::walk_expr
  24: rustc_hir::intravisit::walk_expr
  25: rustc_hir::intravisit::walk_body
  26: rustc_hir::intravisit::walk_trait_item
  27: <rustc_typeck::collect::CollectItemTypesVisitor as rustc_hir::intravisit::Visitor>::visit_trait_item
  28: rustc_middle::hir::map::Map::visit_item_likes_in_module
  29: rustc_typeck::collect::collect_mod_item_types
  30: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::collect_mod_item_types>::compute
  31: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  32: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  33: rustc_query_system::query::plumbing::get_query_impl
  34: rustc_query_system::query::plumbing::ensure_query_impl
  35: rustc_typeck::check_crate
  36: rustc_interface::passes::analysis
  37: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::analysis>::compute
  38: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  39: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  40: rustc_query_system::query::plumbing::get_query_impl
  41: rustc_middle::ty::context::tls::enter_global
  42: rustc_interface::interface::run_compiler_in_existing_thread_pool
  43: rustc_ast::attr::with_globals
<backtrace>

[jonas-schievink]

Please try this on the newest nightly

[scull7]

I attempted to compile on nightly using with cargo +nightly build, received the following error:

thread 'rustc' panicked at 'called `Option::unwrap()` on a `None` value', compiler/rustc_middle/src/hir/map/mod.rs:178:30
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

error: internal compiler error: unexpected panic

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.48.0-nightly (9b4154193 2020-09-14) running on x86_64-apple-darwin

note: compiler flags: -C embed-bitcode=no -C debuginfo=2 -C incremental -C linker=clang --crate-type lib

note: some of the compiler flags provided by cargo are hidden

[jyn514]

Possibly related to #71104.

[fanninpm]

Playground link, for reference.

Have you tried it with the latest nightly this time around? I can't get it to ICE with rustc 1.48.0-nightly (fb1dc34a8 2020-09-21) (on both Mac and the playground).

[Dylan-DPC]

This no longer ICEs and the current output is:

error: cannot find attribute `async_trait` in this scope
 --> src/lib.rs:1:3
  |
1 | #[async_trait]
  |   ^^^^^^^^^^^
  |
  = help: consider importing this attribute macro:
          async_trait::async_trait
  = note: `async_trait` is in scope, but it is a crate, not an attribute

error[[E0706]](https://doc.rust-lang.org/nightly/error_codes/E0706.html): functions in traits cannot be declared `async`
 --> src/lib.rs:7:5
  |
7 |     async fn get_thing(&self) -> anyhow::Result<Self::Item>;
  |     -----^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |     |
  |     `async` because of this
  |
  = note: `async` trait functions are not currently supported
  = note: consider using the `async-trait` crate: https://crates.io/crates/async-trait
  = note: [see issue #91611 <https://github.com/rust-lang/rust/issues/91611>](https://github.com/rust-lang/rust/issues/91611) for more information
  = help: [add `#![feature(async_fn_in_trait)]`](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=c4034bf4f00df0a1b23a57ad19bbd30e#) to the crate attributes to enable

For more information about this error, try `rustc --explain E0706`.
error: could not compile `playground` (lib) due to 2 previous errors