rustc panics compiling async_trait with an associated type

[hirrolot]

rustc panics if I define an associated type inside an #[async_trait] trait and implement it for a structure:

Inside src/main.rs:

#[macro_use]
extern crate async_trait;

#[async_trait]
trait MyTrait {
    type MyType;

    async fn call_boxed(&self) -> Self::MyType;
}

struct MyStruct;

#[async_trait]
impl MyTrait for MyStruct {
    type MyType = i32;

    async fn call_boxed(&self) -> Self::MyType {
        self.call().await
    }
}

impl MyStruct {
    async fn call(&self) -> Self::Output {
        5
    }
}

fn main() {}

Inside Cargo.toml:

[package]
name = "bug"
version = "0.1.0"
edition = "2018"

[dependencies]
async-trait = "0.1.15"

Meta

$ RUST_BACKTRACE=1 cargo check --verbose
       Fresh unicode-xid v0.2.0
       Fresh proc-macro2 v1.0.5
       Fresh quote v1.0.2
       Fresh syn v1.0.5
       Fresh async-trait v0.1.15
    Checking bug v0.1.0 (/home/gymmasssorla/bug)
     Running `rustc --edition=2018 --crate-name bug src/main.rs --color always --crate-type bin --emit=dep-info,metadata -C debuginfo=2 -C metadata=8e79409b6a7339ca -C extra-filename=-8e79409b6a7339ca --out-dir /home/gymmasssorla/bug/target/debug/deps -C incremental=/home/gymmasssorla/bug/target/debug/incremental -L dependency=/home/gymmasssorla/bug/target/debug/deps --extern async_trait=/home/gymmasssorla/bug/target/debug/deps/libasync_trait-447b246b76a3f45f.so`
error[E0223]: ambiguous associated type
  --> src/main.rs:23:29
   |
23 |     async fn call(&self) -> Self::Output {
   |                             ^^^^^^^^^^^^ help: use fully-qualified syntax: `<MyStruct as Trait>::Output`

thread 'rustc' panicked at 'called `Option::unwrap()` on a `None` value', src/libcore/option.rs:378:21
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/git.colasdn.top-1ecc6299db9ec823/backtrace-0.3.37/src/backtrace/libunwind.rs:88
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/git.colasdn.top-1ecc6299db9ec823/backtrace-0.3.37/src/backtrace/mod.rs:66
   2: std::sys_common::backtrace::_print_fmt
             at src/libstd/sys_common/backtrace.rs:77
   3: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
             at src/libstd/sys_common/backtrace.rs:61
   4: core::fmt::write
             at src/libcore/fmt/mod.rs:1028
   5: std::io::Write::write_fmt
             at src/libstd/io/mod.rs:1412
   6: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:65
   7: std::sys_common::backtrace::print
             at src/libstd/sys_common/backtrace.rs:50
   8: std::panicking::default_hook::{{closure}}
             at src/libstd/panicking.rs:189
   9: std::panicking::default_hook
             at src/libstd/panicking.rs:206
  10: rustc_driver::report_ice
  11: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:473
  12: std::panicking::continue_panic_fmt
             at src/libstd/panicking.rs:376
  13: rust_begin_unwind
             at src/libstd/panicking.rs:303
  14: core::panicking::panic_fmt
             at src/libcore/panicking.rs:84
  15: core::panicking::panic
             at src/libcore/panicking.rs:49
  16: rustc_typeck::check::closure::<impl rustc_typeck::check::FnCtxt>::supplied_sig_of_closure
  17: rustc_typeck::check::closure::<impl rustc_typeck::check::FnCtxt>::check_expr_closure
  18: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_kind
  19: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_with_expectation_and_needs
  20: rustc_typeck::check::FnCtxt::check_argument_types
  21: rustc_typeck::check::callee::<impl rustc_typeck::check::FnCtxt>::confirm_builtin_call
  22: rustc_typeck::check::callee::<impl rustc_typeck::check::FnCtxt>::check_call
  23: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_kind
  24: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_with_expectation_and_needs
  25: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_return_expr
  26: rustc_typeck::check::check_fn
  27: rustc::ty::context::GlobalCtxt::enter_local
  28: rustc_typeck::check::typeck_tables_of
  29: rustc::ty::query::__query_compute::typeck_tables_of
  30: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::typeck_tables_of>::compute
  31: rustc::dep_graph::graph::DepGraph::with_task_impl
  32: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  33: rustc::ty::query::__query_compute::typeck_tables_of
  34: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::typeck_tables_of>::compute
  35: rustc::dep_graph::graph::DepGraph::with_task_impl
  36: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  37: rustc_typeck::collect::checked_type_of
  38: rustc_typeck::collect::type_of
  39: rustc::ty::query::__query_compute::type_of
  40: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::type_of>::compute
  41: rustc::dep_graph::graph::DepGraph::with_task_impl
  42: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  43: rustc::hir::intravisit::walk_expr
  44: rustc::hir::intravisit::Visitor::visit_fn
  45: rustc::hir::intravisit::walk_impl_item
  46: rustc::hir::map::Map::visit_item_likes_in_module
  47: rustc_typeck::collect::collect_mod_item_types
  48: rustc::ty::query::__query_compute::collect_mod_item_types
  49: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::collect_mod_item_types>::compute
  50: rustc::dep_graph::graph::DepGraph::with_task_impl
  51: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  52: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::ensure_query
  53: rustc_typeck::check_crate::{{closure}}::{{closure}}
  54: rustc::util::common::time
  55: rustc_typeck::check_crate
  56: rustc_interface::passes::analysis
  57: rustc::ty::query::__query_compute::analysis
  58: rustc::dep_graph::graph::DepGraph::with_task_impl
  59: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  60: rustc_interface::passes::BoxedGlobalCtxt::access::{{closure}}
  61: rustc_interface::passes::create_global_ctxt::{{closure}}
  62: rustc_interface::passes::BoxedGlobalCtxt::enter
  63: rustc_interface::interface::run_compiler_in_existing_thread_pool
  64: std::thread::local::LocalKey<T>::with
  65: scoped_tls::ScopedKey<T>::set
  66: syntax::with_globals
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose 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 1.40.0-nightly (1721c9685 2019-10-12) running on x86_64-unknown-linux-gnu

note: compiler flags: -C debuginfo=2 -C incremental --crate-type bin

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

query stack during panic:
#0 [typeck_tables_of] processing `MyStruct::call`
#1 [typeck_tables_of] processing `MyStruct::call::{{closure}}#0`
#2 [type_of] processing `MyStruct::call::{{closure}}#0`
#3 [collect_mod_item_types] collecting item types in top-level module
#4 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to previous error

For more information about this error, try `rustc --explain E0223`.
error: could not compile `bug`.

Caused by:
  process didn't exit successfully: `rustc --edition=2018 --crate-name bug src/main.rs --color always --crate-type bin --emit=dep-info,metadata -C debuginfo=2 -C metadata=8e79409b6a7339ca -C extra-filename=-8e79409b6a7339ca --out-dir /home/gymmasssorla/bug/target/debug/deps -C incremental=/home/gymmasssorla/bug/target/debug/incremental -L dependency=/home/gymmasssorla/bug/target/debug/deps --extern async_trait=/home/gymmasssorla/bug/target/debug/deps/libasync_trait-447b246b76a3f45f.so` (exit code: 101)

[hirrolot]

Why E-needs-mcve?

[jonas-schievink]

@Gymmasssorla Your code still depends on async_trait, which does rather heavy code generation. You might be able to minimize the example further by running cargo expand.

[hirrolot]

@jonas-schievink

I have executed cargo expand and fixed some compilation errors, but now the compiler doesn't panic at all. Is it a bug raised by async-trait?

trait MyTrait {
    type MyType;
    fn call_boxed<'life0, 'async_trait>(
        &'life0 self,
    ) -> ::core::pin::Pin<
        Box<
            dyn ::core::future::Future<Output = Self::MyType> + ::core::marker::Send + 'async_trait,
        >,
    >
    where
        'life0: 'async_trait,
        Self: 'async_trait;
}
struct MyStruct;
impl MyTrait for MyStruct {
    type MyType = i32;
    fn call_boxed<'life0, 'async_trait>(
        &'life0 self,
    ) -> ::core::pin::Pin<
        Box<
            dyn ::core::future::Future<Output = Self::MyType> + ::core::marker::Send + 'async_trait,
        >,
    >
    where
        'life0: 'async_trait,
        Self: 'async_trait,
    {
        #[allow(clippy::used_underscore_binding)]
        async fn __call_boxed(_self: &MyStruct) -> <MyStruct as MyTrait>::MyType {
            _self.call().await
        }
        Box::pin(__call_boxed(self))
    }
}
impl MyStruct {
    async fn call(&self) -> Self::Output {
        5
    }
}
fn main() {}

The playground link: https://play.rust-lang.org/?version=nightly&mode=debug&edition=2018&gist=f0658bacf89df3cd99dfa092c82ffd9a.

[bbigras]

I might have a minimal case:

rustc 1.40.0-nightly (e413dc3 2019-10-14)

[dependencies]
tiberius = "0.3.2"

use tiberius::transaction::Transaction;

async fn suivi_log(
    conn: Transaction<std::boxed::Box<dyn tiberius::BoxableIo>>,
) -> Transaction<std::boxed::Box<dyn tiberius::BoxableIo>> {
    conn
}

fn main() {}

error[E0603]: module `transaction` is private
 --> src/main.rs:1:15
  |
1 | use tiberius::transaction::Transaction;
  |               ^^^^^^^^^^^

thread 'rustc' panicked at 'called `Option::unwrap()` on a `None` value', src/libcore/option.rs:378:21
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/git.colasdn.top-1ecc6299db9ec823/backtrace-0.3.37/src/backtrace/libunwind.rs:88
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/git.colasdn.top-1ecc6299db9ec823/backtrace-0.3.37/src/backtrace/mod.rs:66
   2: std::sys_common::backtrace::_print_fmt
             at src/libstd/sys_common/backtrace.rs:77
   3: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
             at src/libstd/sys_common/backtrace.rs:61
   4: core::fmt::write
             at src/libcore/fmt/mod.rs:1028
   5: std::io::Write::write_fmt
             at src/libstd/io/mod.rs:1412
   6: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:65
   7: std::sys_common::backtrace::print
             at src/libstd/sys_common/backtrace.rs:50
   8: std::panicking::default_hook::{{closure}}
             at src/libstd/panicking.rs:189
   9: std::panicking::default_hook
             at src/libstd/panicking.rs:206
  10: rustc_driver::report_ice
  11: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:473
  12: std::panicking::continue_panic_fmt
             at src/libstd/panicking.rs:376
  13: rust_begin_unwind
             at src/libstd/panicking.rs:303
  14: core::panicking::panic_fmt
             at src/libcore/panicking.rs:84
  15: core::panicking::panic
             at src/libcore/panicking.rs:49
  16: rustc_typeck::check::closure::<impl rustc_typeck::check::FnCtxt>::supplied_sig_of_closure
  17: rustc_typeck::check::closure::<impl rustc_typeck::check::FnCtxt>::check_expr_closure
  18: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_kind
  19: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_with_expectation_and_needs
  20: rustc_typeck::check::FnCtxt::check_argument_types
  21: rustc_typeck::check::callee::<impl rustc_typeck::check::FnCtxt>::confirm_builtin_call
  22: rustc_typeck::check::callee::<impl rustc_typeck::check::FnCtxt>::check_call
  23: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_kind
  24: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_expr_with_expectation_and_needs
  25: rustc_typeck::check::expr::<impl rustc_typeck::check::FnCtxt>::check_return_expr
  26: rustc_typeck::check::check_fn
  27: rustc::ty::context::GlobalCtxt::enter_local
  28: rustc_typeck::check::typeck_tables_of
  29: rustc::ty::query::__query_compute::typeck_tables_of
  30: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::typeck_tables_of>::compute
  31: rustc::dep_graph::graph::DepGraph::with_task_impl
  32: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  33: rustc::ty::query::__query_compute::typeck_tables_of
  34: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::typeck_tables_of>::compute
  35: rustc::dep_graph::graph::DepGraph::with_task_impl
  36: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  37: rustc_typeck::collect::checked_type_of
  38: rustc_typeck::collect::type_of
  39: rustc::ty::query::__query_compute::type_of
  40: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::type_of>::compute
  41: rustc::dep_graph::graph::DepGraph::with_task_impl
  42: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  43: rustc::hir::intravisit::walk_expr
  44: rustc::hir::intravisit::Visitor::visit_fn
  45: rustc::hir::intravisit::walk_item
  46: <rustc_typeck::collect::CollectItemTypesVisitor as rustc::hir::intravisit::Visitor>::visit_item
  47: rustc::hir::map::Map::visit_item_likes_in_module
  48: rustc_typeck::collect::collect_mod_item_types
  49: rustc::ty::query::__query_compute::collect_mod_item_types
  50: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors for rustc::ty::query::queries::collect_mod_item_types>::compute
  51: rustc::dep_graph::graph::DepGraph::with_task_impl
  52: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  53: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::ensure_query
  54: rustc_typeck::check_crate::{{closure}}::{{closure}}
  55: rustc::util::common::time
  56: rustc_typeck::check_crate
  57: rustc_interface::passes::analysis
  58: rustc::ty::query::__query_compute::analysis
  59: rustc::dep_graph::graph::DepGraph::with_task_impl
  60: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt>::get_query
  61: rustc_interface::passes::BoxedGlobalCtxt::access::{{closure}}
  62: rustc_interface::passes::create_global_ctxt::{{closure}}
  63: rustc_interface::passes::BoxedGlobalCtxt::enter
  64: rustc_interface::interface::run_compiler_in_existing_thread_pool
  65: std::thread::local::LocalKey<T>::with
  66: scoped_tls::ScopedKey<T>::set
  67: syntax::with_globals
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose 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 1.40.0-nightly (e413dc36a 2019-10-14) running on x86_64-unknown-linux-gnu

note: compiler flags: -C debuginfo=2 -C incremental --crate-type bin

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

query stack during panic:
#0 [typeck_tables_of] processing `suivi_log`
#1 [typeck_tables_of] processing `suivi_log::{{closure}}#0`
#2 [type_of] processing `suivi_log::{{closure}}#0`
#3 [collect_mod_item_types] collecting item types in top-level module
#4 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to previous error

For more information about this error, try `rustc --explain E0603`.
error: could not compile `rs-suivi`.

To learn more, run the command again with --verbose.

[estebank]

I can no longer reproduce this with a fresh master build and I believe this was fixed by https://github.com/rust-lang/rust/pull/65235/files#diff-35fad773654cfed45bea0a2abcbe12a6L691-L692

cc @nikomatsakis

[hirrolot]

I am too, closing the issue.