rust-lang / rust-lang/rust

ICE: `error performing ParamEnvAnd { ... }` possibly related to (lack of) HRTBs in closures

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A-closures A-higher-ranked A-trait-system C-bug fixed-by-next-solver I-ICE S-bug-has-test T-compiler
Dominant language
Rust
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Description

Credits to @kvverti for finding the following ICE while experimenting with some of my code that was producing HRTB-related errors.

Code
#![allow(warnings)]

trait Foo {}

impl<F> Foo for F where F: FnMut(&()) {}

struct Bar<F> {
    f: F,
}

impl<F> Foo for Bar<F> where F: Foo {}

fn assert_foo<F>(_: F)
where
    Bar<F>: Foo,
{
}

fn main() {
    assert_foo(|_| ());
}
Meta

rustc --version --verbose:

rustc 1.77.2 (25ef9e3d8 2024-04-09)
binary: rustc
commit-hash: 25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04
commit-date: 2024-04-09
host: x86_64-pc-windows-msvc
release: 1.77.2
LLVM version: 17.0.6
Error output

Command: cargo build

note: no errors encountered even though `span_delayed_bug` issued

note: those delayed bugs will now be shown as internal compiler errors

error: internal compiler error: error performing ParamEnvAnd { param_env: ParamEnv { caller_bounds: [], reveal: UserFacing }, value: ProvePredicate { predicate: Binder { value: TraitPredicate(<Bar<{closure@src\main.rs:20:16: 20:19}> as Foo>, polarity:Positive), bound_vars: [] } } }
  --> src\main.rs:20:5
   |
20 |     assert_foo(|_| ());
   |     ^^^^^^^^^^^^^^^^^^
   |
note: delayed at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04\compiler\rustc_trait_selection\src\traits\query\type_op\mod.rs:164:29 - disabled backtrace    
  --> src\main.rs:20:5
   |
20 |     assert_foo(|_| ());
   |     ^^^^^^^^^^^^^^^^^^

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 1.77.2 (25ef9e3d8 2024-04-09) running on x86_64-pc-windows-msvc

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

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

query stack during panic:
end of query stack
error: could not compile `rustc-ice-mre` (bin "rustc-ice-mre")
Backtrace 

note: no errors encountered even though `span_delayed_bug` issued

note: those delayed bugs will now be shown as internal compiler errors

error: internal compiler error: error performing ParamEnvAnd { param_env: ParamEnv { caller_bounds: [], reveal: UserFacing }, value: ProvePredicate { predicate: Binder { value: TraitPredicate(<Bar<{closure@src\main.rs:20:16: 20:19}> as Foo>, polarity:Positive), bound_vars: [] } } }
  --> src\main.rs:20:5
   |
20 |     assert_foo(|_| ());
   |     ^^^^^^^^^^^^^^^^^^
   |
note: delayed at /rustc/25ef9e3d85d934b27d9dada2f9dd52b1dc63bb04\compiler\rustc_trait_selection\src\traits\query\type_op\mod.rs:164:29
         0: std::backtrace::Backtrace::force_capture
         1: std::backtrace::Backtrace::capture
         2: <rustc_errors::DiagCtxt>::flush_delayed
         3: <rustc_errors::DiagCtxt>::emit_diagnostic
         4: <rustc_errors::diagnostic::Diagnostic as core::cmp::PartialEq>::eq
         5: <rustc_borrowck::type_check::liveness::local_use_map::LocalUseMapBuild as rustc_middle::mir::visit::Visitor>::visit_local
         6: <rustc_borrowck::type_check::TypeVerifier as rustc_middle::mir::visit::Visitor>::visit_body
         7: <rustc_borrowck::type_check::TypeVerifier as rustc_middle::mir::visit::Visitor>::visit_constant
         8: <rustc_borrowck::type_check::TypeVerifier as rustc_middle::mir::visit::Visitor>::visit_body
         9: <rustc_borrowck::type_check::relate_tys::NllTypeRelatingDelegate as rustc_infer::infer::relate::nll::TypeRelatingDelegate>::push_outlives
        10: <rustc_borrowck::member_constraints::MemberConstraintSet<rustc_middle::ty::sty::RegionVid> as core::default::Default>::default
        11: <rustc_borrowck::MirBorrowckCtxt>::consume_operand
        12: rustc_borrowck::mir_borrowck
        13: <rustc_query_impl::plumbing::QueryCtxt as rustc_query_system::query::QueryContext>::load_side_effects
        14: rustc_query_impl::query_callbacks
        15: <rustc_query_impl::plumbing::QueryCtxt as rustc_query_system::query::QueryContext>::load_side_effects
        16: <rustc_query_impl::plumbing::QueryCtxt as rustc_query_system::query::QueryContext>::load_side_effects
        17: rustc_interface::proc_macro_decls::proc_macro_decls_static
        18: <time::date_time::DateTime<time::date_time::offset_kind::Fixed> as core::convert::From<std::time::SystemTime>>::from
        19: rustc_interface::passes::analysis
        20: rustc_query_impl::profiling_support::alloc_self_profile_query_strings
        21: rustc_query_impl::profiling_support::alloc_self_profile_query_strings
        22: rustc_query_impl::profiling_support::alloc_self_profile_query_strings
        23: rustc_query_impl::profiling_support::alloc_self_profile_query_strings
        24: rustc_query_impl::profiling_support::alloc_self_profile_query_strings
        25: rustc_driver_impl::args::arg_expand_all
        26: rustc_driver_impl::args::arg_expand_all
        27: <rustc_middle::ty::SymbolName as core::fmt::Debug>::fmt
        28: <rustc_middle::ty::SymbolName as core::fmt::Debug>::fmt
        29: <rustc_middle::ty::SymbolName as core::fmt::Debug>::fmt
        30: std::sys::pal::windows::thread::Thread::new
        31: BaseThreadInitThunk
        32: RtlUserThreadStart
  --> src\main.rs:20:5
   |
20 |     assert_foo(|_| ());
   |     ^^^^^^^^^^^^^^^^^^

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 1.77.2 (25ef9e3d8 2024-04-09) running on x86_64-pc-windows-msvc

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

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

query stack during panic:
end of query stack
error: could not compile `rustc-ice-mre` (bin "rustc-ice-mre")

Notes

The code compiles successfully if the closure is explicitly typed like so:

assert_foo(|_: &()| ()); // OK

Or if an identify function is used like so:

fn id<F: FnMut(&())>(f: F) -> F { f }

assert_foo(id(|_| ())); // OK

My original code produces an error (not ICE) that seems to be a diagnostics bug, complaining about trait bounds not being satisfied when it should really state something along the lines of implementation of FnMut is not general enough.
An MRE is provided below.

Original code and error 

trait Foo {}

impl<F> Foo for F where F: FnMut(&()) {}

struct Bar<F> {
    f: F,
}

impl<F> Foo for Bar<F> where F: Foo {}

fn main() -> impl Foo {
    Bar { f: (|a| ()) }
}

error[E0277]: the trait bound `Bar<{closure@src\main.rs:12:15: 12:18}>: Foo` is not satisfied
  --> src\main.rs:11:14
   |
11 | fn main() -> impl Foo {
   |              ^^^^^^^^ the trait `Foo` is not implemented for `Bar<{closure@src\main.rs:12:15: 12:18}>`
   |
   = help: the trait `Foo` is implemented for `Bar<{closure@src\main.rs:12:15: 12:18}>`

error[E0277]: `main` has invalid return type `impl Foo`
  --> src\main.rs:11:14
   |
11 | fn main() -> impl Foo {
   |              ^^^^^^^^ `main` can only return types that implement `Termination`
   |
   = help: consider using `()`, or a `Result`

For more information about this error, try `rustc --explain E0277`.
error: could not compile `rustc-ice-mre` (bin "rustc-ice-mre") due to 2 previous errors

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by reproducing the minimal example with the listed rustc 1.77.2 toolchain and compare it with the explicitly typed and identity-function variants. The relevant compiler location named in the report is compiler/rustc_trait_selection/src/traits/query/type_op/mod.rs:164; investigate the ParamEnvAnd/ProvePredicate ICE and verify that the original example produces a diagnostic rather than an internal compiler error.

Written by the indexing model from the issue text.

Assessment

Tech stack
rust
Domain
compilers
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Clearly specified
Newbie friendliness
38/100

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