ICE: compiler/rustc_middle/src/ty/sty.rs:399:33: upvar_tys called before capture types are inferred

[chengniansun]

Code

fn server() -> impl {
    ().map2(|| "")
}
trait FilterBase2 {
    fn map2<F>(self, F) -> Map2<F> {}
}
struct Map2<segment2> {
    _func: F,
}
impl<F> FilterBase2 for F {}

Meta

rustc --version --verbose:

rustc 1.49.0-nightly (338f939a8 2020-11-02)
binary: rustc
commit-hash: 338f939a8d77061896cd0a1ca87a2c6d1f4ec359
commit-date: 2020-11-02
host: x86_64-unknown-linux-gnu
release: 1.49.0-nightly

Error output

error: at least one trait must be specified
 --> reduced-mutant.rs:1:16
  |
1 | fn server() -> impl {
  |                ^^^^

error[E0412]: cannot find type `F` in this scope
  --> reduced-mutant.rs:8:12
   |
8  |       _func: F,
   |              ^
   |
help: a trait with a similar name exists
   |
8  |     _func: Fn,
   |            ^^
help: you might be missing a type parameter
   |
7  | struct Map2<segment2, F> {
   |                     ^^^

warning: type parameter `segment2` should have an upper camel case name
 --> reduced-mutant.rs:7:13
  |
7 | struct Map2<segment2> {
  |             ^^^^^^^^ help: convert the identifier to upper camel case (notice the capitalization): `Segment2`
  |
  = note: `#[warn(non_camel_case_types)]` on by default

error[E0601]: `main` function not found in crate `reduced_mutant`
  --> reduced-mutant.rs:1:1
   |
1  | / fn server() -> impl {
2  | |     ().map2(|| "")
3  | | }
4  | | trait FilterBase2 {
...  |
9  | | }
10 | | impl<F> FilterBase2 for F {}
   | |____________________________^ consider adding a `main` function to `reduced-mutant.rs`

error: internal compiler error: /rustc/338f939a8d77061896cd0a1ca87a2c6d1f4ec359/compiler/rustc_middle/src/ty/sty.rs:399:33: upvar_tys called before capture types are inferred

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 1.49.0-nightly (338f939a8 2020-11-02) running on x86_64-unknown-linux-gnu

query stack during panic:
#0 [typeck] type-checking `server`
#1 [mir_built] building MIR for `server`
end of query stack
error: aborting due to 4 previous errors; 1 warning emitted

Some errors have detailed explanations: E0412, E0601.
For more information about an error, try `rustc --explain E0412`.

Backtrace

thread 'rustc' panicked at 'Box<Any>', compiler/rustc_errors/src/lib.rs:958:9
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_middle::ty::sty::ClosureSubsts::upvar_tys
   9: <rustc_trait_selection::opaque_types::ConstrainOpaqueTypeRegionVisitor<OP> as rustc_middle::ty::fold::TypeVisitor>::visit_ty
  10: <core::iter::adapters::Copied<I> as core::iter::traits::iterator::Iterator>::try_fold
  11: rustc_middle::ty::structural_impls::<impl rustc_middle::ty::fold::TypeFoldable for &rustc_middle::ty::TyS>::super_visit_with
  12: <rustc_trait_selection::opaque_types::ConstrainOpaqueTypeRegionVisitor<OP> as rustc_middle::ty::fold::TypeVisitor>::visit_ty
  13: <rustc_infer::infer::InferCtxt as rustc_trait_selection::opaque_types::InferCtxtExt>::constrain_opaque_types
  14: rustc_typeck::check::regionck::RegionCtxt::visit_fn_body
  15: rustc_hir::intravisit::walk_expr
  16: <rustc_typeck::check::regionck::RegionCtxt as rustc_hir::intravisit::Visitor>::visit_expr
  17: rustc_hir::intravisit::walk_expr
  18: <rustc_typeck::check::regionck::RegionCtxt as rustc_hir::intravisit::Visitor>::visit_expr
  19: <rustc_typeck::check::regionck::RegionCtxt as rustc_hir::intravisit::Visitor>::visit_expr
  20: rustc_typeck::check::regionck::RegionCtxt::visit_fn_body
  21: rustc_typeck::check::regionck::<impl rustc_typeck::check::fn_ctxt::FnCtxt>::regionck_fn
  22: rustc_infer::infer::InferCtxtBuilder::enter
  23: rustc_typeck::check::typeck
  24: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  25: rustc_data_structures::stack::ensure_sufficient_stack
  26: rustc_query_system::query::plumbing::get_query_impl
  27: rustc_middle::ty::context::TyCtxt::typeck_opt_const_arg
  28: rustc_mir_build::thir::cx::Cx::new
  29: rustc_infer::infer::InferCtxtBuilder::enter
  30: rustc_mir_build::build::mir_built
  31: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::mir_built>::compute
  32: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  33: rustc_data_structures::stack::ensure_sufficient_stack
  34: rustc_query_system::query::plumbing::get_query_impl
  35: rustc_mir::transform::check_unsafety::unsafety_check_result
  36: core::ops::function::FnOnce::call_once
  37: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::unsafety_check_result>::compute
  38: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  39: rustc_data_structures::stack::ensure_sufficient_stack
  40: rustc_query_system::query::plumbing::get_query_impl
  41: rustc_query_system::query::plumbing::ensure_query_impl
  42: rustc_mir::transform::mir_const
  43: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::mir_const>::compute
  44: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  45: rustc_data_structures::stack::ensure_sufficient_stack
  46: rustc_query_system::query::plumbing::get_query_impl
  47: rustc_mir::transform::mir_promoted
  48: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::mir_promoted>::compute
  49: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  50: rustc_data_structures::stack::ensure_sufficient_stack
  51: rustc_query_system::query::plumbing::get_query_impl
  52: rustc_mir::borrow_check::mir_borrowck
  53: core::ops::function::FnOnce::call_once
  54: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::mir_borrowck>::compute
  55: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  56: rustc_data_structures::stack::ensure_sufficient_stack
  57: rustc_query_system::query::plumbing::get_query_impl
  58: rustc_typeck::collect::type_of::type_of
  59: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::type_of>::compute
  60: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  61: rustc_data_structures::stack::ensure_sufficient_stack
  62: rustc_query_system::query::plumbing::get_query_impl
  63: rustc_typeck::check::check::check_item_type
  64: rustc_middle::hir::map::Map::visit_item_likes_in_module
  65: rustc_typeck::check::check::check_mod_item_types
  66: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::check_mod_item_types>::compute
  67: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  68: rustc_data_structures::stack::ensure_sufficient_stack
  69: rustc_query_system::query::plumbing::get_query_impl
  70: rustc_query_system::query::plumbing::ensure_query_impl
  71: rustc_session::utils::<impl rustc_session::session::Session>::time
  72: rustc_typeck::check_crate
  73: rustc_interface::passes::analysis
  74: rustc_middle::ty::query::<impl rustc_query_system::query::config::QueryAccessors<rustc_middle::ty::context::TyCtxt> for rustc_middle::ty::query::queries::analysis>::compute
  75: rustc_query_system::dep_graph::graph::DepGraph<K>::with_task_impl
  76: rustc_data_structures::stack::ensure_sufficient_stack
  77: rustc_query_system::query::plumbing::get_query_impl
  78: rustc_interface::passes::QueryContext::enter

NOTE: The bug is found by our work-in-progress compiler testing tool Kira, and the test program is reduced/minimized by Perses

[jyn514]

@chengniansun does this still panic after #78432 ? That only merged a couple days ago so you'll need to update your version of nightly.

[jyn514]

Hmm I checked and it does, and it also panics before. So probably unrelated?

cc @arora-aman just in case

[jyn514]

Note that this works fine on +nightly-2020-06-22.

[chengniansun]

@chengniansun does this still panic after #78432 ? That only merged a couple days ago so you'll need to update your version of nightly.

[chengniansun]

Sorry, I accidentally closed the issue.

@jyn514 Yes, you are right. It still crashes on the latest nightly version. I have a cron job to update my rust version everyday.

[arora-aman]

I think we ended up (incorrectly) removing a check in a64ad51#diff-98923b31651a0150fc5eae47f5ceb44f716b521762db4e37cf9292dac7b3e040L724-L733

We shouldn't be calling upvars_ty if tupled_upvars_ty is ty::Infer. This is a separate issue than that was fixed in #78432

[arora-aman]

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