ICE `no successor`

[matthiaskrgr]

auto-reduced (treereduce-rust):

#![feature(guard_patterns)]

fn main() {
    match (0,) {
        (_ if { let main = false; main },) => {}
        _ => {}
    }
}

original:

//@ check-pass
//! Test that `GatherLocalsVisitor` only visits expressions in guard patterns when checking the
//! expressions, and not a second time when visiting the pattern. If locals are declared inside the
//! the guard expression, it would ICE if visited twice ("evaluated expression more than once").

#![feature(guard_patterns)]
#![expect(guard_patterns)]

fn main() {
    match (0,) {
        // FIXME(guard_patterns): liveness lints don't work yet; this will ICE without the `_`.
        (_ if { let main = false; main },) => {
    match (0,) {
        // FIXME(guard_patterns): liveness lints don't work yet; this will ICE without the `_`.
        (_ if { let _x = false; _x },) => {}
        _ => {}
    }
}
        _ => {}
    }
}

Version information

rustc 1.91.0-nightly (f4665ab83 2025-09-10)
binary: rustc
commit-hash: f4665ab8368ad2e8a86d4390ae35c28bdd9561bb
commit-date: 2025-09-10
host: x86_64-unknown-linux-gnu
release: 1.91.0-nightly
LLVM version: 21.1.0

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

Program output

warning: the feature `guard_patterns` is incomplete and may not be safe to use and/or cause compiler crashes
 --> /tmp/icemaker_global_tempdir.lrrS5NseB5VV/rustc_testrunner_tmpdir_reporting.IHAQeISeUx35/mvce.rs:1:12
  |
1 | #![feature(guard_patterns)]
  |            ^^^^^^^^^^^^^^
  |
  = note: see issue #129967 <https://github.com/rust-lang/rust/issues/129967> for more information
  = note: `#[warn(incomplete_features)]` on by default

warning: unreachable pattern
 --> /tmp/icemaker_global_tempdir.lrrS5NseB5VV/rustc_testrunner_tmpdir_reporting.IHAQeISeUx35/mvce.rs:6:9
  |
5 |         (_ if { let main = false; main },) => {}
  |         ---------------------------------- matches any value
6 |         _ => {}
  |         ^ no value can reach this
  |
  = note: `#[warn(unreachable_patterns)]` (part of `#[warn(unused)]`) on by default

warning: variable `main` is assigned to, but never used
 --> /tmp/icemaker_global_tempdir.lrrS5NseB5VV/rustc_testrunner_tmpdir_reporting.IHAQeISeUx35/mvce.rs:5:21
  |
5 |         (_ if { let main = false; main },) => {}
  |                     ^^^^
  |
  = note: consider using `_main` instead
  = note: `#[warn(unused_variables)]` (part of `#[warn(unused)]`) on by default

warning: 3 warnings emitted

note: no errors encountered even though delayed bugs were created

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

error: internal compiler error: no successor
  |
  = note: delayed at compiler/rustc_passes/src/liveness.rs:575:35
             0: <rustc_errors::DiagCtxtInner>::emit_diagnostic
             1: <rustc_errors::DiagCtxtHandle>::emit_diagnostic
             2: <rustc_span::ErrorGuaranteed as rustc_errors::diagnostic::EmissionGuarantee>::emit_producing_guarantee
             3: <rustc_passes::liveness::Liveness>::report_unused
             4: rustc_hir::intravisit::walk_block::<rustc_passes::liveness::Liveness>
             5: <rustc_passes::liveness::Liveness as rustc_hir::intravisit::Visitor>::visit_expr
             6: <rustc_passes::liveness::Liveness as rustc_hir::intravisit::Visitor>::visit_pat
             7: <rustc_passes::liveness::Liveness as rustc_hir::intravisit::Visitor>::visit_expr
             8: rustc_hir::intravisit::walk_block::<rustc_passes::liveness::Liveness>
             9: <rustc_passes::liveness::Liveness as rustc_hir::intravisit::Visitor>::visit_expr
            10: rustc_passes::liveness::check_liveness
            11: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::check_liveness::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 0]>>
            12: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_data_structures::vec_cache::VecCache<rustc_span::def_id::LocalDefId, rustc_middle::query::erase::Erased<[u8; 0]>, rustc_query_system::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
            13: rustc_query_impl::query_impl::check_liveness::get_query_non_incr::__rust_end_short_backtrace
            14: rustc_mir_build::builder::build_mir
            15: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::mir_built::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 8]>>
            16: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_data_structures::vec_cache::VecCache<rustc_span::def_id::LocalDefId, rustc_middle::query::erase::Erased<[u8; 8]>, rustc_query_system::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
            17: rustc_query_impl::query_impl::mir_built::get_query_non_incr::__rust_end_short_backtrace
            18: rustc_mir_build::check_unsafety::check_unsafety
            19: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::check_unsafety::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 0]>>
            20: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_data_structures::vec_cache::VecCache<rustc_span::def_id::LocalDefId, rustc_middle::query::erase::Erased<[u8; 0]>, rustc_query_system::dep_graph::graph::DepNodeIndex>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
            21: rustc_query_impl::query_impl::check_unsafety::get_query_non_incr::__rust_end_short_backtrace
            22: <rustc_middle::ty::context::TyCtxt>::par_hir_body_owners::<rustc_interface::passes::run_required_analyses::{closure#1}::{closure#0}>::{closure#0}
            23: rustc_interface::passes::analysis
            24: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 0]>>
            25: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::SingleCache<rustc_middle::query::erase::Erased<[u8; 0]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
            26: rustc_query_impl::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
            27: rustc_interface::passes::create_and_enter_global_ctxt::<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>::{closure#2}::{closure#0}
            28: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}
            29: std::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface::util::run_in_thread_with_globals<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
            30: <<std::thread::Builder>::spawn_unchecked_<rustc_interface::util::run_in_thread_with_globals<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
            31: std::sys::pal::unix::thread::Thread::new::thread_start
            32: <unknown>
            33: <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 1.91.0-nightly (f4665ab83 2025-09-10) running on x86_64-unknown-linux-gnu

query stack during panic:
end of query stack

@rustbot label +F-guard_patterns

[matthiaskrgr]

formatted

#![feature(guard_patterns)]
fn main() {
    match (0,) {
        (
            _ if {
          let main;
          main
        },
        ) => {}
    }
}

seems to biscect to nightly-2025-01-09

[dianne]

This happens because liveness linting isn't implemented for guard patterns. It should be fixed by #142390.

[Aditya-PS-05]

@rustbot claim