rust-lang / rust-lang/rust

ICE upvar_tys called before capture types are inferred

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A-diagnostics C-bug I-ICE needs-triage P-medium regression-untriaged T-compiler WG-trait-system-refactor
Dominant language
Rust
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Description

snippet:

fn main() {
    Some([0]).map(|s| s[..]);
}

Version information

rustc 1.100.0-nightly (752b9bf87 2026-09-07)
binary: rustc
commit-hash: 752b9bf8798c2ffc1d3fe2b804c04454366fc6d6
commit-date: 2026-09-07
host: x86_64-unknown-linux-gnu
release: 1.100.0-nightly
LLVM version: 23.1.1

Possibly related line of code:
https://github.com/rust-lang/rust/blob/752b9bf8798c2ffc1d3fe2b804c04454366fc6d6/compiler/rustc_middle/src/ty/sty.rs#L194-L206

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc

Program output 

error[E0277]: the size for values of type `[{integer}]` cannot be known at compilation time
    --> /tmp/icemaker_global_tempdir.y4oxhmSBkaRU/rustc_testrunner_tmpdir_reporting.4aRXUhCYUxEe/mvce.rs:2:15
     |
   2 |     Some([0]).map(|s| s[..]);
     |               ^^^ doesn't have a size known at compile-time
     |
     = help: the trait `Sized` is not implemented for `[{integer}]`
note: required by an implicit `Sized` bound in `Option::<T>::map`
    --> /home/matthias/.rustup/toolchains/master/lib/rustlib/src/rust/library/core/src/option.rs:1160:22
     |
1160 |     pub const fn map<U, F>(self, f: F) -> Option<U>
     |                      ^ required by the implicit `Sized` requirement on this type parameter in `Option::<T>::map`

error[E0277]: the size for values of type `[{integer}]` cannot be known at compilation time
 --> /tmp/icemaker_global_tempdir.y4oxhmSBkaRU/rustc_testrunner_tmpdir_reporting.4aRXUhCYUxEe/mvce.rs:2:23
  |
2 |     Some([0]).map(|s| s[..]);
  |                       ^^^^^ doesn't have a size known at compile-time
  |
  = help: the trait `Sized` is not implemented for `[{integer}]`
  = note: the return type of a function must have a statically known size

error: internal compiler error: /rustc-dev/752b9bf8798c2ffc1d3fe2b804c04454366fc6d6/compiler/rustc_middle/src/ty/sty.rs:200:33: upvar_tys called before capture types are inferred


thread 'rustc' (2995014) panicked at /rustc-dev/752b9bf8798c2ffc1d3fe2b804c04454366fc6d6/compiler/rustc_middle/src/ty/sty.rs:200:33:
Box<dyn Any>
stack backtrace:
   0:     0x7f6b7ead5b46 - <<std[7799338267317a1]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[feb819e0aab98535]::fmt::Display>::fmt
   1:     0x7f6b7f2081cf - core[feb819e0aab98535]::fmt::write
   2:     0x7f6b7eaeac0c - <std[7799338267317a1]::sys::stdio::unix::Stderr as core[feb819e0aab98535]::io::write::Write>::write_fmt
   3:     0x7f6b7eaa83ea - std[7799338267317a1]::panicking::default_hook::{closure#0}
   4:     0x7f6b7eac9e43 - std[7799338267317a1]::panicking::default_hook
   5:     0x7f6b7da1338f - std[7799338267317a1]::panicking::update_hook::<alloc[eddc929262330b86]::boxed::Box<rustc_driver_impl[93e22c4ae85d6128]::install_ice_hook::{closure#1}>>::{closure#0}
   6:     0x7f6b7eaca2e2 - std[7799338267317a1]::panicking::panic_with_hook
   7:     0x7f6b7da41c44 - std[7799338267317a1]::panicking::begin_panic::<rustc_errors[ccb98f0a5bff281a]::ExplicitBug>::{closure#0}
   8:     0x7f6b7da3a71e - std[7799338267317a1]::sys::backtrace::__rust_end_short_backtrace::<std[7799338267317a1]::panicking::begin_panic<rustc_errors[ccb98f0a5bff281a]::ExplicitBug>::{closure#0}, !>
   9:     0x7f6b7da387be - std[7799338267317a1]::panicking::begin_panic::<rustc_errors[ccb98f0a5bff281a]::ExplicitBug>
  10:     0x7f6b7da4d511 - <rustc_errors[ccb98f0a5bff281a]::diagnostic::BugAbort as rustc_errors[ccb98f0a5bff281a]::diagnostic::EmissionGuarantee>::emit_producing_guarantee
  11:     0x7f6b7dff4cb9 - rustc_middle[95f7c36db503aa5c]::util::bug::opt_span_bug_fmt::<rustc_span[aab65db9cf037f3]::span_encoding::Span>::{closure#0}
  12:     0x7f6b7dff50f2 - rustc_middle[95f7c36db503aa5c]::ty::context::tls::with_opt::<rustc_middle[95f7c36db503aa5c]::util::bug::opt_span_bug_fmt<rustc_span[aab65db9cf037f3]::span_encoding::Span>::{closure#0}, !>::{closure#0}
  13:     0x7f6b7dfdfeb0 - rustc_middle[95f7c36db503aa5c]::ty::context::tls::with_context_opt::<rustc_middle[95f7c36db503aa5c]::ty::context::tls::with_opt<rustc_middle[95f7c36db503aa5c]::util::bug::opt_span_bug_fmt<rustc_span[aab65db9cf037f3]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  14:     0x7f6b7aca83d4 - rustc_middle[95f7c36db503aa5c]::util::bug::bug_fmt
  15:     0x7f6b7e7e4b70 - <rustc_trait_selection[b2c49a93e168dccb]::error_reporting::TypeErrCtxt>::note_closure_capture::<rustc_span[aab65db9cf037f3]::ErrorGuaranteed>
  16:     0x7f6b7e7f9e1f - <rustc_trait_selection[b2c49a93e168dccb]::error_reporting::TypeErrCtxt>::note_obligation_cause_code_inner::<rustc_span[aab65db9cf037f3]::ErrorGuaranteed, rustc_middle[95f7c36db503aa5c]::ty::predicate::Predicate>
  17:     0x7f6b7e7e4c36 - <rustc_trait_selection[b2c49a93e168dccb]::error_reporting::TypeErrCtxt>::note_obligation_cause_code::<rustc_span[aab65db9cf037f3]::ErrorGuaranteed, rustc_middle[95f7c36db503aa5c]::ty::predicate::Predicate>
  18:     0x7f6b7e8f1d1c - <rustc_trait_selection[b2c49a93e168dccb]::error_reporting::TypeErrCtxt>::note_obligation_cause
  19:     0x7f6b7e8de797 - <rustc_trait_selection[b2c49a93e168dccb]::error_reporting::TypeErrCtxt>::report_selection_error
  20:     0x7f6b7e905fc9 - <rustc_trait_selection[b2c49a93e168dccb]::error_reporting::TypeErrCtxt>::report_fulfillment_error
  21:     0x7f6b7d298d3c - <rustc_trait_selection[b2c49a93e168dccb]::error_reporting::TypeErrCtxt>::report_fulfillment_errors
  22:     0x7f6b7f2f3426 - <rustc_hir_typeck[74465e21f53f1374]::fn_ctxt::FnCtxt>::resolve_vars_with_obligations::<rustc_middle[95f7c36db503aa5c]::ty::Ty>
  23:     0x7f6b7fd33cde - <rustc_hir_typeck[74465e21f53f1374]::fn_ctxt::FnCtxt>::check_expr_with_expectation_and_args
  24:     0x7f6b7fd28105 - <rustc_hir_typeck[74465e21f53f1374]::fn_ctxt::FnCtxt>::check_expr_block
  25:     0x7f6b7fd2f155 - <rustc_hir_typeck[74465e21f53f1374]::fn_ctxt::FnCtxt>::check_expr_with_expectation_and_args
  26:     0x7f6b7fd13258 - rustc_hir_typeck[74465e21f53f1374]::check::check_fn
  27:     0x7f6b8067a55b - rustc_hir_typeck[74465e21f53f1374]::typeck_with_inspect::{closure#0}
  28:     0x7f6b80678b7a - rustc_query_impl[bdd1a1285068393]::query_vtables::typeck_root::invoke_provider_fn::__rust_begin_short_backtrace
  29:     0x7f6b7f879535 - rustc_query_impl[bdd1a1285068393]::execution::try_execute_query::<rustc_data_structures[b3e0016b95cb4620]::vec_cache::VecCache<rustc_span[aab65db9cf037f3]::def_id::LocalDefId, rustc_middle[95f7c36db503aa5c]::query::erase::ErasedData<[u8; 8usize]>, rustc_middle[95f7c36db503aa5c]::dep_graph::graph::DepNodeIndex>, false>
  30:     0x7f6b7f879167 - rustc_query_impl[bdd1a1285068393]::query_vtables::typeck_root::execute_query_non_incr::__rust_end_short_backtrace
  31:     0x7f6b7f93566f - <rustc_middle[95f7c36db503aa5c]::ty::context::TyCtxt>::par_hir_body_owners::<rustc_hir_analysis[3f6e10ab2280337c]::check_crate::{closure#1}>::{closure#0}
  32:     0x7f6b7f93492e - rustc_hir_analysis[3f6e10ab2280337c]::check_crate
  33:     0x7f6b7f87aaf3 - rustc_interface[1845d939591a8dca]::passes::analysis
  34:     0x7f6b8049d7ca - rustc_query_impl[bdd1a1285068393]::execution::try_execute_query::<rustc_middle[95f7c36db503aa5c]::query::caches::SingleCache<rustc_middle[95f7c36db503aa5c]::query::erase::ErasedData<[u8; 0usize]>>, false>
  35:     0x7f6b8049d56b - rustc_query_impl[bdd1a1285068393]::query_vtables::analysis::execute_query_non_incr::__rust_end_short_backtrace
  36:     0x7f6b8054bb4c - rustc_interface[1845d939591a8dca]::interface::run_compiler::<(), rustc_driver_impl[93e22c4ae85d6128]::run_compiler::{closure#0}>::{closure#2}
  37:     0x7f6b80628f42 - std[7799338267317a1]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[1845d939591a8dca]::util::run_in_thread_with_globals<rustc_interface[1845d939591a8dca]::util::run_in_thread_pool_with_globals<rustc_interface[1845d939591a8dca]::interface::run_compiler<(), rustc_driver_impl[93e22c4ae85d6128]::run_compiler::{closure#0}>::{closure#2}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  38:     0x7f6b80628ced - <std[7799338267317a1]::thread::lifecycle::spawn_unchecked<rustc_interface[1845d939591a8dca]::util::run_in_thread_with_globals<rustc_interface[1845d939591a8dca]::util::run_in_thread_pool_with_globals<rustc_interface[1845d939591a8dca]::interface::run_compiler<(), rustc_driver_impl[93e22c4ae85d6128]::run_compiler::{closure#0}>::{closure#2}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[feb819e0aab98535]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  39:     0x7f6b80631607 - <std[7799338267317a1]::sys::thread::unix::Thread>::new::thread_start
  40:     0x7f6b796980a2 - <unknown>
  41:     0x7f6b7972080c - <unknown>
  42:                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 1.100.0-nightly (752b9bf87 2026-09-07) running on x86_64-unknown-linux-gnu

query stack during panic:
#0 [typeck_root] type-checking `main`
#1 [analysis] running analysis passes on crate `mvce`
end of query stack
error: aborting due to 3 previous errors

For more information about this error, try `rustc --explain E0277`.

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

Run the supplied a.rs reproducer with the reported nightly and inspect compiler/rustc_middle/src/ty/sty.rs around upvar_tys. Trace the typeck_root path and rustc_trait_selection error-reporting path shown in the backtrace. Done means the example reports its type errors without triggering the 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
Active
Clarity
Mostly clear
Newbie friendliness
48/100

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