Internal compiler error: compiler/rustc_trait_selection/src/traits/codegen.rs:78:17

[someguynamedjosh]

Code

trait Output<'a> {
    type Type;
    fn convert() -> Self::Type;
}

impl<'a> Output<'a> for i32 {
    type Type = i32;
    
    fn convert() -> i32 {
        0
    }
}

struct Wrapper;

impl Wrapper {
    fn do_something_wrapper<O, F>(&mut self, use_output: F)
    where
        O: for<'a> Output<'a>,
        F: for<'a> FnOnce(<O as Output<'a>>::Type)
    {
        let output = <O as Output>::convert();
        use_output(output)
    }
}

fn main() {
    let mut wrapper = Wrapper;
    wrapper.do_something_wrapper::<i32, _>(|value| ());
}

Meta

Using Rust Playground's nightly build:

Nightly channel
Build using the Nightly version: 1.50.0-nightly
(2020-11-30 b7ebc6b0c1ba3c27ebb1)

Error output

   Compiling playground v0.0.1 (/playground)
warning: unused variable: `value`
  --> src/main.rs:29:45
   |
29 |     wrapper.do_something_wrapper::<i32, _>(|value| ());
   |                                             ^^^^^ help: if this is intentional, prefix it with an underscore: `_value`
   |
   = note: `#[warn(unused_variables)]` on by default

error: internal compiler error: compiler/rustc_trait_selection/src/traits/codegen.rs:78:17: Encountered error `OutputTypeParameterMismatch(Binder(<[closure@src/main.rs:29:44: 29:54] as std::ops::FnOnce<(<i32 as Output<'_>>::Type,)>>), Binder(<[closure@src/main.rs:29:44: 29:54] as std::ops::FnOnce<(i32,)>>), Sorts(ExpectedFound { expected: i32, found: <i32 as Output<'_>>::Type }))` selecting `Binder(<[closure@src/main.rs:29:44: 29:54] as std::ops::FnOnce<(i32,)>>)` during codegen

thread 'rustc' panicked at 'Box<Any>', compiler/rustc_errors/src/lib.rs:958:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

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 1.50.0-nightly (b7ebc6b0c 2020-11-30) running on x86_64-unknown-linux-gnu

note: compiler flags: -C embed-bitcode=no -C codegen-units=1 -C debuginfo=2 --crate-type bin

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

query stack during panic:
#0 [codegen_fulfill_obligation] checking if `std::ops::FnOnce` fulfills its obligations
#1 [resolve_instance] resolving instance `<[closure@src/main.rs:29:44: 29:54] as std::ops::FnOnce<(i32,)>>::call_once`
end of query stack
error: aborting due to previous error; 1 warning emitted

error: could not compile `playground`

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

Backtrace

(On my own computer with the stable build)

rustc 1.48.0 (7eac88abb 2020-11-16)
binary: rustc
commit-hash: 7eac88abb2e57e752f3302f02be5f3ce3d7adfb4
commit-date: 2020-11-16
host: x86_64-unknown-linux-gnu
release: 1.48.0
LLVM version: 11.0

   Compiling bug v0.1.0 (/tmp/bug)
warning: unused variable: `value`
  --> src/main.rs:29:45
   |
29 |     wrapper.do_something_wrapper::<i32, _>(|value| ());
   |                                             ^^^^^ help: if this is intentional, prefix it with an underscore: `_value`
   |
   = note: `#[warn(unused_variables)]` on by default

error: internal compiler error: compiler/rustc_trait_selection/src/traits/codegen/mod.rs:75:17: Encountered error `OutputTypeParameterMismatch(Binder(<[closure@src/main.rs:29:44: 29:54] as std::ops::FnOnce<(<i32 as Output<'_>>::Type,)>>), Binder(<[closure@src/main.rs:29:44: 29:54] as std::ops::FnOnce<(i32,)>>), Sorts(ExpectedFound { expected: i32, found: <i32 as Output<'_>>::Type }))` selecting `Binder(<[closure@src/main.rs:29:44: 29:54] as std::ops::FnOnce<(i32,)>>)` during codegen

thread 'rustc' panicked at 'Box<Any>', compiler/rustc_errors/src/lib.rs:945:9
stack backtrace:
   0: std::panicking::begin_panic
   1: rustc_errors::HandlerInner::bug
   2: rustc_errors::Handler::bug
   3: rustc_middle::util::bug::opt_span_bug_fmt::{{closure}}
   4: rustc_middle::ty::context::tls::with_opt::{{closure}}
   5: rustc_middle::ty::context::tls::with_opt
   6: rustc_middle::util::bug::opt_span_bug_fmt
   7: rustc_middle::util::bug::bug_fmt
   8: rustc_infer::infer::InferCtxtBuilder::enter
   9: rustc_trait_selection::traits::codegen::codegen_fulfill_obligation
  10: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::codegen_fulfill_obligation>::compute
  11: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  12: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  13: rustc_data_structures::stack::ensure_sufficient_stack
  14: rustc_query_system::query::plumbing::get_query_impl
  15: rustc_ty::instance::inner_resolve_instance
  16: rustc_ty::instance::resolve_instance
  17: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::resolve_instance>::compute
  18: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  19: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  20: rustc_data_structures::stack::ensure_sufficient_stack
  21: rustc_query_system::query::plumbing::get_query_impl
  22: rustc_middle::ty::instance::Instance::resolve_opt_const_arg
  23: rustc_middle::ty::instance::Instance::resolve
  24: <rustc_mir::monomorphize::collector::MirNeighborCollector as rustc_middle::mir::visit::Visitor>::visit_terminator
  25: rustc_mir::monomorphize::collector::collect_neighbours
  26: rustc_mir::monomorphize::collector::collect_items_rec
  27: rustc_mir::monomorphize::collector::collect_items_rec
  28: rustc_session::utils::<impl rustc_session::session::Session>::time
  29: rustc_mir::monomorphize::collector::collect_crate_mono_items
  30: rustc_mir::monomorphize::partitioning::collect_and_partition_mono_items
  31: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::collect_and_partition_mono_items>::compute
  32: rustc_middle::dep_graph::<impl rustc_query_system::dep_graph::DepKind for rustc_middle::dep_graph::dep_node::DepKind>::with_deps
  33: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  34: rustc_data_structures::stack::ensure_sufficient_stack
  35: rustc_query_system::query::plumbing::get_query_impl
  36: rustc_codegen_ssa::base::codegen_crate
  37: <rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_ssa::traits::backend::CodegenBackend>::codegen_crate
  38: rustc_session::utils::<impl rustc_session::session::Session>::time
  39: rustc_interface::passes::QueryContext::enter
  40: rustc_interface::queries::Queries::ongoing_codegen
  41: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
  42: rustc_span::with_source_map
  43: scoped_tls::ScopedKey<T>::set
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

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 (7eac88abb 2020-11-16) running on x86_64-unknown-linux-gnu

note: compiler flags: -C embed-bitcode=no -C debuginfo=2 -C incremental --crate-type bin

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

query stack during panic:
#0 [codegen_fulfill_obligation] checking if `std::ops::FnOnce` fulfills its obligations
#1 [resolve_instance] resolving instance `<[closure@src/main.rs:29:44: 29:54] as std::ops::FnOnce<(i32,)>>::call_once`
#2 [collect_and_partition_mono_items] collect_and_partition_mono_items
end of query stack
error: aborting due to previous error; 1 warning emitted

error: could not compile `bug`

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

[connorskees]

a bit smaller,

trait Output<'a> {
    type Type;
    fn convert() -> Self::Type;
}

impl<'a> Output<'a> for i32 {
    type Type = ();

    fn convert() {}
}

fn do_something<O, F>(use_output: F)
where
    O: for<'a> Output<'a>,
    F: for<'a> FnOnce(<O as Output<'a>>::Type),
{
    use_output(O::convert())
}

fn main() {
    do_something::<i32, _>(|value| ());
}

[jonas-schievink]

(also happens on stable, not a regression)

[jackh726]

Closing as duplicate of #62529