ICE: BoundRegion { var: 0, kind: BrNamed(DefId(0:9 ~ rust_bug[3fc9]::or::'a), 'a) } is a region but value is Type(_)

[cfcosta]

I don't have much context on this, was doing some thinkering on what would be the best way to do something not really interesting, and got this ICE. This bug happens on both Nightly and Stable.

Code

This is the original code I managed to replicate the issue:

pub struct Something;

type Validator<'a> = dyn 'a + Send + Sync + Fn(&'a Something) -> Result<(), ()>;

pub static ALL_VALIDATORS: &[(&'static str, &'static Validator)] = &[(
    "validate that credits and debits balance",
    &validate_something,
)];

fn or<'a>(first: &'static Validator<'a>, second: &'static Validator<'a>) -> Validator<'a> {
    return Box::new(move |something: &'_ Something| -> Result<(), ()> {
        first(something).or_else(|_| second(something))
    })
}

fn validate_something(_: &Something) -> Result<(), ()> {
    Ok(())
}

fn main() {}

This code fails with the ICE error. Removing the return on the Box of the or function turns it from an ICE to a normal compiler error.

A member on the Rust discord (@5225225) also reported that this, more minimal test case also returns the same error:

fn or<'a>(first: &'static (dyn Fn(&'a i32))) -> dyn 'a + Fn(&'a i32) {
   return Box::new(panic!());
}

fn main() {}

Meta

rustc +nightly --version --verbose:

rustc 1.59.0-nightly (48a5999fc 2021-12-01)
binary: rustc
commit-hash: 48a5999fceeea84a8971634355287faa349909d4
commit-date: 2021-12-01
host: x86_64-unknown-linux-gnu
release: 1.59.0-nightly
LLVM version: 13.0.0

rustc +stable --version --verbose:

rustc 1.57.0 (f1edd0429 2021-11-29)
binary: rustc
commit-hash: f1edd0429582dd29cccacaf50fd134b05593bd9c
commit-date: 2021-11-29
host: x86_64-unknown-linux-gnu
release: 1.57.0
LLVM version: 13.0.0

Error output

error: internal compiler error: /rustc/48a5999fceeea84a8971634355287faa349909d4/compiler/rustc_infer/src/infer/canonical/substitute.rs:76:18: BoundRegion { var: 0, kind: BrNamed(DefId(0:9 ~ rust_bug[3fc9]::or::'a), 'a) } is a region but value is Type(_)

thread 'rustc' panicked at 'Box<dyn Any>', compiler/rustc_errors/src/lib.rs:1171:9
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 1.59.0-nightly (48a5999fc 2021-12-01) running on x86_64-unknown-linux-gnu

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

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

query stack during panic:
#0 [evaluate_obligation] evaluating trait selection obligation `for<'a> alloc::boxed::Box<[closure@src/main.rs:11:21: 13:6]>: core::ops::function::Fn<(&'a Something,)>`
#1 [typeck] type-checking `or`
end of query stack
error: could not compile `rust-bug`

Backtrace

error: internal compiler error: /rustc/48a5999fceeea84a8971634355287faa349909d4/compiler/rustc_infer/src/infer/canonical/substitute.rs:76:18: BoundRegion { var: 0, kind: BrNamed(DefId(0:9 ~ rust_bug[3fc9]::or::'a), 'a) } is a region but value is Type(_)

thread 'rustc' panicked at 'Box<dyn Any>', compiler/rustc_errors/src/lib.rs:1171:9
stack backtrace:
   0: std::panicking::begin_panic::<rustc_errors::ExplicitBug>
   1: std::panic::panic_any::<rustc_errors::ExplicitBug>
   2: <rustc_errors::HandlerInner>::bug
   3: <rustc_errors::Handler>::bug
   4: rustc_middle::ty::context::tls::with_opt::<rustc_middle::util::bug::opt_span_bug_fmt<rustc_span::span_encoding::Span>::{closure#0}, ()>
   5: rustc_middle::util::bug::opt_span_bug_fmt::<rustc_span::span_encoding::Span>
   6: rustc_middle::util::bug::bug_fmt
   7: rustc_infer::infer::canonical::substitute::substitute_value::<rustc_middle::ty::ParamEnvAnd<rustc_middle::traits::query::type_op::Normalize<rustc_middle::ty::Predicate>>>::{closure#0}
   8: <&rustc_middle::ty::TyS as rustc_middle::ty::fold::TypeFoldable>::super_fold_with::<rustc_middle::ty::fold::BoundVarReplacer>
   9: <&rustc_middle::ty::list::List<rustc_middle::ty::subst::GenericArg> as rustc_middle::ty::fold::TypeFoldable>::fold_with::<rustc_middle::ty::fold::BoundVarReplacer>
  10: <&rustc_middle::ty::TyS as rustc_middle::ty::fold::TypeFoldable>::super_fold_with::<rustc_middle::ty::fold::BoundVarReplacer>
  11: <rustc_middle::ty::fold::BoundVarReplacer as rustc_middle::ty::fold::TypeFolder>::fold_predicate
  12: <rustc_infer::infer::InferCtxtBuilder>::enter_with_canonical::<rustc_middle::ty::ParamEnvAnd<rustc_middle::ty::Predicate>, core::result::Result<rustc_middle::traits::select::EvaluationResult, rustc_middle::traits::select::OverflowError>, rustc_traits::evaluate_obligation::evaluate_obligation::{closure#0}>
  13: rustc_traits::evaluate_obligation::evaluate_obligation
  14: <rustc_query_system::dep_graph::graph::DepGraph<rustc_middle::dep_graph::dep_node::DepKind>>::with_task::<rustc_middle::ty::context::TyCtxt, rustc_middle::infer::canonical::Canonical<rustc_middle::ty::ParamEnvAnd<rustc_middle::ty::Predicate>>, core::result::Result<rustc_middle::traits::select::EvaluationResult, rustc_middle::traits::select::OverflowError>>
  15: rustc_data_structures::stack::ensure_sufficient_stack::<(core::result::Result<rustc_middle::traits::select::EvaluationResult, rustc_middle::traits::select::OverflowError>, rustc_query_system::dep_graph::graph::DepNodeIndex), rustc_query_system::query::plumbing::execute_job<rustc_query_impl::plumbing::QueryCtxt, rustc_middle::infer::canonical::Canonical<rustc_middle::ty::ParamEnvAnd<rustc_middle::ty::Predicate>>, core::result::Result<rustc_middle::traits::select::EvaluationResult, rustc_middle::traits::select::OverflowError>>::{closure#3}>
  16: rustc_query_system::query::plumbing::get_query::<rustc_query_impl::queries::evaluate_obligation, rustc_query_impl::plumbing::QueryCtxt>
  17: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::evaluate_obligation
  18: <rustc_infer::infer::InferCtxt as rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt>::predicate_may_hold
  19: <core::iter::adapters::copied::Copied<core::slice::iter::Iter<rustc_middle::ty::sty::Binder<rustc_middle::ty::sty::ExistentialPredicate>>> as core::iter::traits::iterator::Iterator>::try_fold::<(), core::iter::traits::iterator::Iterator::all::check<rustc_middle::ty::sty::Binder<rustc_middle::ty::sty::ExistentialPredicate>, <rustc_infer::infer::InferCtxt as rustc_trait_selection::traits::error_reporting::suggestions::InferCtxtExt>::suggest_impl_trait::{closure#5}::{closure#0}>::{closure#0}, core::ops::control_flow::ControlFlow<()>>
  20: <core::iter::adapters::map::Map<core::iter::adapters::filter_map::FilterMap<core::slice::iter::Iter<&rustc_hir::hir::Expr>, <rustc_infer::infer::InferCtxt as rustc_trait_selection::traits::error_reporting::suggestions::InferCtxtExt>::suggest_impl_trait::{closure#2}>, <rustc_infer::infer::InferCtxt as rustc_trait_selection::traits::error_reporting::suggestions::InferCtxtExt>::suggest_impl_trait::{closure#3}> as core::iter::traits::iterator::Iterator>::try_fold::<(), core::iter::traits::iterator::Iterator::all::check<&rustc_middle::ty::TyS, <rustc_infer::infer::InferCtxt as rustc_trait_selection::traits::error_reporting::suggestions::InferCtxtExt>::suggest_impl_trait::{closure#5}>::{closure#0}, core::ops::control_flow::ControlFlow<()>>
  21: <rustc_infer::infer::InferCtxt as rustc_trait_selection::traits::error_reporting::suggestions::InferCtxtExt>::suggest_impl_trait
  22: <rustc_infer::infer::InferCtxt as rustc_trait_selection::traits::error_reporting::InferCtxtExt>::report_selection_error
  23: <rustc_infer::infer::InferCtxt as rustc_trait_selection::traits::error_reporting::InferCtxtPrivExt>::report_fulfillment_error
  24: <rustc_infer::infer::InferCtxt as rustc_trait_selection::traits::error_reporting::InferCtxtExt>::report_fulfillment_errors
  25: <rustc_typeck::check::fn_ctxt::FnCtxt>::type_inference_fallback
  26: <rustc_infer::infer::InferCtxtBuilder>::enter::<&rustc_middle::ty::context::TypeckResults, <rustc_typeck::check::inherited::InheritedBuilder>::enter<rustc_typeck::check::typeck_with_fallback<rustc_typeck::check::typeck::{closure#0}>::{closure#1}, &rustc_middle::ty::context::TypeckResults>::{closure#0}>
  27: rustc_typeck::check::typeck
  28: <rustc_query_system::dep_graph::graph::DepGraph<rustc_middle::dep_graph::dep_node::DepKind>>::with_task::<rustc_middle::ty::context::TyCtxt, rustc_span::def_id::LocalDefId, &rustc_middle::ty::context::TypeckResults>
  29: rustc_data_structures::stack::ensure_sufficient_stack::<(&rustc_middle::ty::context::TypeckResults, rustc_query_system::dep_graph::graph::DepNodeIndex), rustc_query_system::query::plumbing::execute_job<rustc_query_impl::plumbing::QueryCtxt, rustc_span::def_id::LocalDefId, &rustc_middle::ty::context::TypeckResults>::{closure#3}>
  30: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::plumbing::QueryCtxt, rustc_query_system::query::caches::DefaultCache<rustc_span::def_id::LocalDefId, &rustc_middle::ty::context::TypeckResults>>
  31: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::typeck
  32: rustc_typeck::check::typeck
  33: <rustc_query_system::dep_graph::graph::DepGraph<rustc_middle::dep_graph::dep_node::DepKind>>::with_task::<rustc_middle::ty::context::TyCtxt, rustc_span::def_id::LocalDefId, &rustc_middle::ty::context::TypeckResults>
  34: rustc_data_structures::stack::ensure_sufficient_stack::<(&rustc_middle::ty::context::TypeckResults, rustc_query_system::dep_graph::graph::DepNodeIndex), rustc_query_system::query::plumbing::execute_job<rustc_query_impl::plumbing::QueryCtxt, rustc_span::def_id::LocalDefId, &rustc_middle::ty::context::TypeckResults>::{closure#3}>
  35: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::plumbing::QueryCtxt, rustc_query_system::query::caches::DefaultCache<rustc_span::def_id::LocalDefId, &rustc_middle::ty::context::TypeckResults>>
  36: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::typeck
  37: <rustc_middle::hir::map::Map>::par_body_owners::<rustc_typeck::check::typeck_item_bodies::{closure#0}>
  38: rustc_typeck::check::typeck_item_bodies
  39: <rustc_query_system::dep_graph::graph::DepGraph<rustc_middle::dep_graph::dep_node::DepKind>>::with_task::<rustc_middle::ty::context::TyCtxt, (), ()>
  40: rustc_data_structures::stack::ensure_sufficient_stack::<((), rustc_query_system::dep_graph::graph::DepNodeIndex), rustc_query_system::query::plumbing::execute_job<rustc_query_impl::plumbing::QueryCtxt, (), ()>::{closure#3}>
  41: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::plumbing::QueryCtxt, rustc_query_system::query::caches::DefaultCache<(), ()>>
  42: rustc_query_system::query::plumbing::get_query::<rustc_query_impl::queries::typeck_item_bodies, rustc_query_impl::plumbing::QueryCtxt>
  43: <rustc_session::session::Session>::time::<(), rustc_typeck::check_crate::{closure#7}>
  44: rustc_typeck::check_crate
  45: rustc_interface::passes::analysis
  46: <rustc_query_system::dep_graph::graph::DepGraph<rustc_middle::dep_graph::dep_node::DepKind>>::with_task::<rustc_middle::ty::context::TyCtxt, (), core::result::Result<(), rustc_errors::ErrorReported>>
  47: rustc_data_structures::stack::ensure_sufficient_stack::<(core::result::Result<(), rustc_errors::ErrorReported>, rustc_query_system::dep_graph::graph::DepNodeIndex), rustc_query_system::query::plumbing::execute_job<rustc_query_impl::plumbing::QueryCtxt, (), core::result::Result<(), rustc_errors::ErrorReported>>::{closure#3}>
  48: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::plumbing::QueryCtxt, rustc_query_system::query::caches::DefaultCache<(), core::result::Result<(), rustc_errors::ErrorReported>>>
  49: rustc_query_system::query::plumbing::get_query::<rustc_query_impl::queries::analysis, rustc_query_impl::plumbing::QueryCtxt>
  50: <rustc_interface::passes::QueryContext>::enter::<rustc_driver::run_compiler::{closure#1}::{closure#2}::{closure#3}, core::result::Result<(), rustc_errors::ErrorReported>>
  51: <rustc_interface::interface::Compiler>::enter::<rustc_driver::run_compiler::{closure#1}::{closure#2}, core::result::Result<core::option::Option<rustc_interface::queries::Linker>, rustc_errors::ErrorReported>>
  52: rustc_span::with_source_map::<core::result::Result<(), rustc_errors::ErrorReported>, rustc_interface::interface::create_compiler_and_run<core::result::Result<(), rustc_errors::ErrorReported>, rustc_driver::run_compiler::{closure#1}>::{closure#1}>
  53: <scoped_tls::ScopedKey<rustc_span::SessionGlobals>>::set::<rustc_interface::util::setup_callbacks_and_run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<core::result::Result<(), rustc_errors::ErrorReported>, rustc_driver::run_compiler::{closure#1}>::{closure#0}, core::result::Result<(), rustc_errors::ErrorReported>>::{closure#0}::{closure#0}, core::result::Result<(), rustc_errors::ErrorReported>>
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 1.59.0-nightly (48a5999fc 2021-12-01) running on x86_64-unknown-linux-gnu

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

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

query stack during panic:
#0 [evaluate_obligation] evaluating trait selection obligation `for<'a> alloc::boxed::Box<[closure@src/main.rs:11:21: 13:6]>: core::ops::function::Fn<(&'a Something,)>`
#1 [typeck] type-checking `or`
#2 [typeck] type-checking `or::{closure#0}::{closure#0}`
#3 [typeck_item_bodies] type-checking all item bodies
#4 [analysis] running analysis passes on this crate
end of query stack

[5225225]

fn or<'a>(first: &'static (dyn Fn(&'a i32))) -> dyn Fn(&'a i32) {
   return Box::new(panic!());
}

This ICEs in the playground, but interestingly, this does not

fn or<'a>(first: &'static (dyn Fn(&'a i32))) -> dyn Fn(&'a i32) {
    Box::new(panic!())
}

Also, the <'a> is needed, you can't use &'static for all of the lifetimes. Same with just dropping the &'a i32 and taking an i32 directly, that fails to ICE.

[5225225]

also...

trait Foo<'a> {}

fn or<'a>(first: &'static dyn Foo<'a>) -> dyn Foo<'a> {
    return Box::new(panic!());
}

also ICEs but it's a different ICE. Fun! I'll go report that.

[5225225]

Reported that ICE as #91803, the root cause might be similar.

[cfcosta]

Thanks for all the help @5225225!

[5225225]

Bisected this

Looks like --regress=ice is acting weirdly. I'm re-running the bisect with a script that greps for "BoundRegion" and it's finding different nightlies. Maybe the behaviour in that commit that confuses bisect-rustc.

********************************************************************************
Regression in nightly-2021-04-01
********************************************************************************

fetching https://static.rust-lang.org/dist/2021-03-31/channel-rust-nightly-git-commit-hash.txt
nightly manifest 2021-03-31: 40 B / 40 B [===========================================] 100.00 % 638.13 KB/s converted 2021-03-31 to 74874a690bc95443292496ff5df5cc5c8cb56e0b
fetching https://static.rust-lang.org/dist/2021-04-01/channel-rust-nightly-git-commit-hash.txt
nightly manifest 2021-04-01: 40 B / 40 B [===========================================] 100.00 % 575.33 KB/s converted 2021-04-01 to 4fdac23f3171e2f8864d359a21da600dd3faafc9
looking for regression commit between 2021-03-31 and 2021-04-01
refreshing repository at "/home/jess/src/rust"
From https://github.com/rust-lang/rust
 * branch                    HEAD       -> FETCH_HEAD
opening existing repository at "/home/jess/src/rust"
fetching (via local git) commits from 74874a690bc95443292496ff5df5cc5c8cb56e0b to 4fdac23f3171e2f8864d359a21da600dd3faafc9
refreshing repository at "/home/jess/src/rust"
From https://github.com/rust-lang/rust
 * branch                    HEAD       -> FETCH_HEAD
opening existing repository at "/home/jess/src/rust"
looking up first commit
looking up second commit
checking that commits are by bors and thus have ci artifacts...
finding bors merge commits
found 6 bors merge commits in the specified range
  commit[0] 2021-03-30UTC: Auto merge of #83652 - xu-cheng:ipv4-octal, r=sfackler
  commit[1] 2021-03-30UTC: Auto merge of #83692 - Dylan-DPC:rollup-2a2m3jy, r=Dylan-DPC
  commit[2] 2021-03-31UTC: Auto merge of #83666 - Amanieu:instrprof-order, r=tmandry
  commit[3] 2021-03-31UTC: Auto merge of #83681 - jyn514:blanket-impls-tweaks, r=Aaron1011
  commit[4] 2021-03-31UTC: Auto merge of #83684 - cjgillot:csp, r=petrochenkov
  commit[5] 2021-03-31UTC: Auto merge of #76814 - jackh726:binder-refactor, r=nikomatsakis
ERROR: no CI builds available between 74874a690bc95443292496ff5df5cc5c8cb56e0b and 4fdac23f3171e2f8864d359a21da600dd3faafc9 within last 167 days

is the new error.