`-Znext-solver`: ICE with closure capturing iterated variable in 2021 edition

[madsmtm]

Code

Using rustc --edition=2021 -Znext-solver=globally foo.rs.

fn main() {
    for item in &[1, 2, 3] {
        let _ = || *item;
    }
}

Manually minimized from original code in objc2, specifically here.

Meta

rustc --version --verbose:

rustc 1.77.0-nightly (30dfb9e04 2024-01-14)
binary: rustc
commit-hash: 30dfb9e046aeb878db04332c74de76e52fb7db10
commit-date: 2024-01-14
host: aarch64-apple-darwin
release: 1.77.0-nightly
LLVM version: 17.0.6

Error output

thread 'rustc' panicked at compiler/rustc_mir_build/src/build/expr/as_place.rs:253:31:
called `Option::unwrap()` on a `None` value

Backtrace

stack backtrace:
   0: _rust_begin_unwind
   1: core::panicking::panic_fmt
   2: core::panicking::panic
   3: core::option::unwrap_failed
   4: <rustc_mir_build::build::Builder>::expr_into_dest
   5: <rustc_mir_build::build::Builder>::in_scope::<<rustc_mir_build::build::Builder>::expr_into_dest::{closure#0}::{closure#0}, ()>
   6: <rustc_mir_build::build::Builder>::expr_into_dest::{closure#0}
   7: <rustc_mir_build::build::Builder>::expr_into_dest
   8: rustc_mir_build::build::mir_build::{closure#0}
   9: rustc_mir_build::build::mir_built
      [... omitted 2 frames ...]
  10: <rustc_mir_build::check_unsafety::UnsafetyVisitor>::visit_inner_body
  11: <rustc_mir_build::check_unsafety::UnsafetyVisitor as rustc_middle::thir::visit::Visitor>::visit_expr
  12: <rustc_mir_build::check_unsafety::UnsafetyVisitor as rustc_middle::thir::visit::Visitor>::visit_expr
  13: rustc_middle::thir::visit::walk_stmt::<rustc_mir_build::check_unsafety::UnsafetyVisitor>
  14: <rustc_mir_build::check_unsafety::UnsafetyVisitor as rustc_middle::thir::visit::Visitor>::visit_block
  15: <rustc_mir_build::check_unsafety::UnsafetyVisitor as rustc_middle::thir::visit::Visitor>::visit_expr
  16: <rustc_mir_build::check_unsafety::UnsafetyVisitor as rustc_middle::thir::visit::Visitor>::visit_expr
  17: rustc_middle::thir::visit::walk_expr::<rustc_mir_build::check_unsafety::UnsafetyVisitor>
  18: <rustc_mir_build::check_unsafety::UnsafetyVisitor as rustc_middle::thir::visit::Visitor>::visit_expr
  19: <rustc_mir_build::check_unsafety::UnsafetyVisitor as rustc_middle::thir::visit::Visitor>::visit_expr
  20: <rustc_mir_build::check_unsafety::UnsafetyVisitor as rustc_middle::thir::visit::Visitor>::visit_block
  21: <rustc_mir_build::check_unsafety::UnsafetyVisitor as rustc_middle::thir::visit::Visitor>::visit_expr
  22: <rustc_mir_build::check_unsafety::UnsafetyVisitor as rustc_middle::thir::visit::Visitor>::visit_expr
  23: <rustc_mir_build::check_unsafety::UnsafetyVisitor as rustc_middle::thir::visit::Visitor>::visit_expr
  24: rustc_middle::thir::visit::walk_expr::<rustc_mir_build::check_unsafety::UnsafetyVisitor>
  25: <rustc_mir_build::check_unsafety::UnsafetyVisitor as rustc_middle::thir::visit::Visitor>::visit_expr
  26: <rustc_mir_build::check_unsafety::UnsafetyVisitor as rustc_middle::thir::visit::Visitor>::visit_expr
  27: <rustc_mir_build::check_unsafety::UnsafetyVisitor as rustc_middle::thir::visit::Visitor>::visit_expr
  28: <rustc_mir_build::check_unsafety::UnsafetyVisitor as rustc_middle::thir::visit::Visitor>::visit_expr
  29: <rustc_mir_build::check_unsafety::UnsafetyVisitor as rustc_middle::thir::visit::Visitor>::visit_expr
  30: <rustc_mir_build::check_unsafety::UnsafetyVisitor as rustc_middle::thir::visit::Visitor>::visit_expr
  31: rustc_mir_build::check_unsafety::check_unsafety
      [... omitted 2 frames ...]
  32: <rustc_middle::hir::map::Map>::par_body_owners::<rustc_interface::passes::analysis::{closure#1}::{closure#0}>::{closure#0}
  33: <rustc_session::session::Session>::time::<(), rustc_interface::passes::analysis::{closure#1}>
  34: rustc_interface::passes::analysis
      [... omitted 2 frames ...]
  35: <rustc_middle::ty::context::GlobalCtxt>::enter::<rustc_driver_impl::run_compiler::{closure#0}::{closure#0}::{closure#3}, core::result::Result<(), rustc_span::ErrorGuaranteed>>
  36: <rustc_interface::interface::Compiler>::enter::<rustc_driver_impl::run_compiler::{closure#0}::{closure#0}, core::result::Result<core::option::Option<rustc_interface::queries::Linker>, rustc_span::ErrorGuaranteed>>
  37: rustc_span::set_source_map::<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_interface::interface::run_compiler<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#0}>::{closure#0}::{closure#0}>
  38: <scoped_tls::ScopedKey<rustc_span::SessionGlobals>>::set::<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#0}>::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>
  39: rustc_span::create_session_globals_then::<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#0}>::{closure#0}, core::result::Result<(), rustc_span::ErrorGuaranteed>>::{closure#0}>
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

[compiler-errors]

Given that this only triggers on edition=2021, I wonder if this has to do with type information used in precise captures. We may need to normalize types in mem-categorization or something 🤔

[matthiaskrgr]

I wonder if this is the same as #119786 but the new solver triggers it more easily

[compiler-errors]

No, that issue #119786 seems to have to do with capturing an upvar which is supposed to have an opaque type. This one has to do with lazy normalization we do in the new solver. Both have to do with bugs in closure upvar computation, but I don't believe they're fixed in the same way.

[matthiaskrgr]

seems to be fixed