ICE: unhandled type unhandled type: &'{erased} mut Closure

[matthiaskrgr]

auto-reduced (treereduce-rust):

pub struct Statement;

pub struct Rows<'stmt>(&'stmt Statement);

impl<'stmt> Iterator for Rows<'stmt> {
    type Item = String;

    fn next() -> Option<Self::Item> {
        let stmt = Statement;
        let rows = Rows(&stmt);
        rows.map(|row| row).next()

        // x
        //
    }
}

fn get_names() -> Option<String> {
    let stmt = Statement;
    let rows = Rows(&stmt);
    rows.map(|row| row).next()

    // x
    //
}

original code

original:

// This is a reduction of a concrete test illustrating a case that was
// annoying to Rust developer stephaneyfx (see issue #46413).
// With resolving issue #54556, pnkfelix hopes that the new diagnostic
// With resolving issue #54556, pnkfelix hopes that the new diagnostic
// output produced by NLL helps to *explain* the semantic significance
// of temp drop order, and thus why storing the result in `x` and then
// returning `x` works.

pub struct Statement;

pub struct Rows<'stmt>(&'stmt Statement);

impl<'stmt> Drop for Option<String> {
    fn drop(&mut self) {}
}

impl<'stmt> Iterator for Rows<'stmt> {
    type Item = String;

    fn next() -> Option<Self::Item> {
    let stmt = Statement;
    let rows = Rows(&stmt); //~ ERROR does not live long enough
    rows.map(|row| row).next()
    // let x = rows.map(|row| row).next();
    // x
    //
    // Removing the map works too as does removing the Drop impl.
}
}

fn drop(&mut self) {}

fn get_names() -> Option<String> {
    let stmt = Statement;
    let rows = Rows(&stmt); //~ ERROR does not live long enough
    rows.map(|row| row).next()
    // let x = rows.map(|row| row).next();
    // x
    //
    // Removing the map works too as does removing the Drop impl.
}

Version information

rustc 1.82.0-nightly (3139ff09e 2024-08-15)
binary: rustc
commit-hash: 3139ff09e9d07f7700f8d15ed25a231e29c43627
commit-date: 2024-08-15
host: x86_64-unknown-linux-gnu
release: 1.82.0-nightly
LLVM version: 19.1.0

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc -Zmir-opt-level=5 -Zvalidate-mir -Zcross-crate-inline-threshold=always

Program output

error[E0601]: `main` function not found in crate `mvce`
  --> /tmp/icemaker_global_tempdir.NrtTvI7Be5z2/rustc_testrunner_tmpdir_reporting.g9SosB3OsY2q/mvce.rs:25:2
   |
25 | }
   |  ^ consider adding a `main` function to `/tmp/icemaker_global_tempdir.NrtTvI7Be5z2/rustc_testrunner_tmpdir_reporting.g9SosB3OsY2q/mvce.rs`

error[E0186]: method `next` has a `&mut self` declaration in the trait, but not in the impl
 --> /tmp/icemaker_global_tempdir.NrtTvI7Be5z2/rustc_testrunner_tmpdir_reporting.g9SosB3OsY2q/mvce.rs:8:5
  |
8 |     fn next() -> Option<Self::Item> {
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected `&mut self` in impl
  |
  = note: `next` from trait: `fn(&mut Self) -> Option<<Self as Iterator>::Item>`

error: internal compiler error: compiler/rustc_mir_transform/src/validate.rs:1491:30: unhandled type: &'{erased} mut Closure(DefId(0:13 ~ mvce[127c]::{impl#0}::next::{closure#0}), ['{erased}, i16, Binder { value: extern "RustCall" fn((std::string::String,)) -> std::string::String, bound_vars: [] }, ()])

thread 'rustc' panicked at compiler/rustc_mir_transform/src/validate.rs:1491:30:
Box<dyn Any>
stack backtrace:
   0:     0x72956f1cb7fd - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::hbd75d7a8055bf739
   1:     0x72956fa04059 - core::fmt::write::h5f25313cecccceeb
   2:     0x7295709aa9d1 - std::io::Write::write_fmt::h17a84ab5b179ddb5
   3:     0x72956f1cdedb - std::panicking::default_hook::{{closure}}::h49f53d56c8f7e527
   4:     0x72956f1cdb4e - std::panicking::default_hook::h00ed981b528c65ea
   5:     0x72956e354309 - std[e33d86a7a723a6e1]::panicking::update_hook::<alloc[f0b0d1fafd7580bd]::boxed::Box<rustc_driver_impl[58349887e35c8b09]::install_ice_hook::{closure#0}>>::{closure#0}
   6:     0x72956f1ce7f7 - std::panicking::rust_panic_with_hook::h3d0aa5d214fe032a
   7:     0x72956e38e671 - std[e33d86a7a723a6e1]::panicking::begin_panic::<rustc_errors[e83ab56271777d9d]::ExplicitBug>::{closure#0}
   8:     0x72956e3816b6 - std[e33d86a7a723a6e1]::sys::backtrace::__rust_end_short_backtrace::<std[e33d86a7a723a6e1]::panicking::begin_panic<rustc_errors[e83ab56271777d9d]::ExplicitBug>::{closure#0}, !>
   9:     0x72956e381436 - std[e33d86a7a723a6e1]::panicking::begin_panic::<rustc_errors[e83ab56271777d9d]::ExplicitBug>
  10:     0x72956e397651 - <rustc_errors[e83ab56271777d9d]::diagnostic::BugAbort as rustc_errors[e83ab56271777d9d]::diagnostic::EmissionGuarantee>::emit_producing_guarantee
  11:     0x72956e95abe4 - rustc_middle[110fa1e98ae6b18b]::util::bug::opt_span_bug_fmt::<rustc_span[179c096983d138e1]::span_encoding::Span>::{closure#0}
  12:     0x72956e9407fa - rustc_middle[110fa1e98ae6b18b]::ty::context::tls::with_opt::<rustc_middle[110fa1e98ae6b18b]::util::bug::opt_span_bug_fmt<rustc_span[179c096983d138e1]::span_encoding::Span>::{closure#0}, !>::{closure#0}
  13:     0x72956e94068b - rustc_middle[110fa1e98ae6b18b]::ty::context::tls::with_context_opt::<rustc_middle[110fa1e98ae6b18b]::ty::context::tls::with_opt<rustc_middle[110fa1e98ae6b18b]::util::bug::opt_span_bug_fmt<rustc_span[179c096983d138e1]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  14:     0x72956c438250 - rustc_middle[110fa1e98ae6b18b]::util::bug::bug_fmt
  15:     0x72956cf744bc - rustc_mir_transform[741e50beaeca447e]::validate::validate_types
  16:     0x72956cf5642e - <rustc_mir_transform[741e50beaeca447e]::validate::Validator as rustc_middle[110fa1e98ae6b18b]::mir::MirPass>::run_pass
  17:     0x72956dc7e930 - rustc_mir_transform[741e50beaeca447e]::pass_manager::validate_body
  18:     0x72956fa02693 - rustc_mir_transform[741e50beaeca447e]::pass_manager::run_passes_inner
  19:     0x7295703d47f7 - rustc_mir_transform[741e50beaeca447e]::optimized_mir
  20:     0x7295703c1c5d - rustc_query_impl[2d64fd05a0316b8c]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[2d64fd05a0316b8c]::query_impl::optimized_mir::dynamic_query::{closure#2}::{closure#0}, rustc_middle[110fa1e98ae6b18b]::query::erase::Erased<[u8; 8usize]>>
  21:     0x72956fa281a7 - rustc_query_system[63eaae8e4727c3d2]::query::plumbing::try_execute_query::<rustc_query_impl[2d64fd05a0316b8c]::DynamicConfig<rustc_query_system[63eaae8e4727c3d2]::query::caches::DefIdCache<rustc_middle[110fa1e98ae6b18b]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[2d64fd05a0316b8c]::plumbing::QueryCtxt, false>
  22:     0x72956fa2775f - rustc_query_impl[2d64fd05a0316b8c]::query_impl::optimized_mir::get_query_non_incr::__rust_end_short_backtrace
  23:     0x72956c537429 - <rustc_middle[110fa1e98ae6b18b]::ty::context::TyCtxt>::instance_mir
  24:     0x729570486506 - rustc_interface[5dc7c791b1753136]::passes::run_required_analyses
  25:     0x72957054369e - rustc_interface[5dc7c791b1753136]::passes::analysis
  26:     0x729570543671 - rustc_query_impl[2d64fd05a0316b8c]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[2d64fd05a0316b8c]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[110fa1e98ae6b18b]::query::erase::Erased<[u8; 1usize]>>
  27:     0x72957096a62e - rustc_query_system[63eaae8e4727c3d2]::query::plumbing::try_execute_query::<rustc_query_impl[2d64fd05a0316b8c]::DynamicConfig<rustc_query_system[63eaae8e4727c3d2]::query::caches::SingleCache<rustc_middle[110fa1e98ae6b18b]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[2d64fd05a0316b8c]::plumbing::QueryCtxt, false>
  28:     0x72957096a38f - rustc_query_impl[2d64fd05a0316b8c]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  29:     0x7295707dd0e9 - rustc_interface[5dc7c791b1753136]::interface::run_compiler::<core[3fe3910426b5ab0e]::result::Result<(), rustc_span[179c096983d138e1]::ErrorGuaranteed>, rustc_driver_impl[58349887e35c8b09]::run_compiler::{closure#0}>::{closure#1}
  30:     0x7295707c6610 - std[e33d86a7a723a6e1]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[5dc7c791b1753136]::util::run_in_thread_with_globals<rustc_interface[5dc7c791b1753136]::util::run_in_thread_pool_with_globals<rustc_interface[5dc7c791b1753136]::interface::run_compiler<core[3fe3910426b5ab0e]::result::Result<(), rustc_span[179c096983d138e1]::ErrorGuaranteed>, rustc_driver_impl[58349887e35c8b09]::run_compiler::{closure#0}>::{closure#1}, core[3fe3910426b5ab0e]::result::Result<(), rustc_span[179c096983d138e1]::ErrorGuaranteed>>::{closure#0}, core[3fe3910426b5ab0e]::result::Result<(), rustc_span[179c096983d138e1]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[3fe3910426b5ab0e]::result::Result<(), rustc_span[179c096983d138e1]::ErrorGuaranteed>>
  31:     0x7295707c6c7a - <<std[e33d86a7a723a6e1]::thread::Builder>::spawn_unchecked_<rustc_interface[5dc7c791b1753136]::util::run_in_thread_with_globals<rustc_interface[5dc7c791b1753136]::util::run_in_thread_pool_with_globals<rustc_interface[5dc7c791b1753136]::interface::run_compiler<core[3fe3910426b5ab0e]::result::Result<(), rustc_span[179c096983d138e1]::ErrorGuaranteed>, rustc_driver_impl[58349887e35c8b09]::run_compiler::{closure#0}>::{closure#1}, core[3fe3910426b5ab0e]::result::Result<(), rustc_span[179c096983d138e1]::ErrorGuaranteed>>::{closure#0}, core[3fe3910426b5ab0e]::result::Result<(), rustc_span[179c096983d138e1]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[3fe3910426b5ab0e]::result::Result<(), rustc_span[179c096983d138e1]::ErrorGuaranteed>>::{closure#1} as core[3fe3910426b5ab0e]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  32:     0x7295707c6feb - std::sys::pal::unix::thread::Thread::new::thread_start::h2aa5d6e6e369f96b
  33:     0x729571f6639d - <unknown>
  34:     0x729571feb49c - <unknown>
  35:                0x0 - <unknown>

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: please make sure that you have updated to the latest nightly

note: rustc 1.82.0-nightly (3139ff09e 2024-08-15) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z mir-opt-level=5 -Z validate-mir -Z cross-crate-inline-threshold=always -Z dump-mir-dir=dir

query stack during panic:
#0 [optimized_mir] optimizing MIR for `get_names`
#1 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to 3 previous errors

Some errors have detailed explanations: E0186, E0601.
For more information about an error, try `rustc --explain E0186`.

[matthiaskrgr]

smaller

//  -Zmir-opt-level=5 -Zvalidate-mir -Zcross-crate-inline-threshold=always
pub struct Rows<'a>();

impl<'a> Iterator for Rows<'a> {
    type Item = ();

    fn next() -> Option<Self::Item> {
        let mut rows = Rows();
        rows.map(|row| row).next()
    }
}

fn main() {
    let mut rows = Rows();
    rows.next();
}