ICE: tcx: index out of bounds: the len is 6 but the index is 6

[matthiaskrgr]

auto-reduced (treereduce-rust):

#![feature(fn_traits, unboxed_closures)]
struct Foo<T>(T);

impl<T: Copy> Fn<()> for Foo<T> {
    fn call(&self, _: ()) -> T {
        match *self {
            Foo(t) => t,
        }
    }
}

impl<T: Copy> FnMut<()> for Foo<T> {}

impl<T: Copy> FnOnce<()> for Foo<T> {
    type Output = T;

    fn call_once(self, _: ()) -> T {
        self.call(())
    }
}

original:

// run-pass
#![feature(fn_traits, unboxed_closures)]
struct Foo<T>(T);

impl<T: Copy> Fn<()> for Foo<T> {
    extern "vectorcall" fn call(&self, _: ()) -> T {
      match *self {
        Foo(t) => t
      }
    }
}

impl<T: Copy> FnMut<()> for Foo<T> {
    extern "rust-call" fn call_mut(&mut self, _: ()) -> T {
        self.call(())
    }
}

impl<T: Copy> FnOnce<()> for Foo<T> {
    type Output = T;

    extern "rust-call" fn call_once(self, _: ()) -> T {
        self.call(())
    }
}

fn main() {
  let t: u8 = 1;
  println!("{}", Foo(t)());
}

Version information

rustc 1.78.0-nightly (9aa232ecc 2024-02-11)
binary: rustc
commit-hash: 9aa232ecc7bb006a1fad404f437b049482021a3a
commit-date: 2024-02-11
host: x86_64-unknown-linux-gnu
release: 1.78.0-nightly
LLVM version: 17.0.6

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc -Zmir-opt-level=0 -Zpolymorphize=on -Zinline-mir=yes

Program output

error[E0601]: `main` function not found in crate `mvce`
  --> /tmp/icemaker_global_tempdir.u1pxKPNyM6gY/rustc_testrunner_tmpdir_reporting.NfvSAW9e4CZU/mvce.rs:20:2
   |
20 | }
   |  ^ consider adding a `main` function to `/tmp/icemaker_global_tempdir.u1pxKPNyM6gY/rustc_testrunner_tmpdir_reporting.NfvSAW9e4CZU/mvce.rs`

error[E0053]: method `call` has an incompatible type for trait
 --> /tmp/icemaker_global_tempdir.u1pxKPNyM6gY/rustc_testrunner_tmpdir_reporting.NfvSAW9e4CZU/mvce.rs:5:5
  |
5 |     fn call(&self, _: ()) -> T {
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^ expected "rust-call" fn, found "Rust" fn
  |
  = note: expected signature `extern "rust-call" fn(&Foo<_>, ()) -> _`
             found signature `fn(&Foo<_>, ()) -> _`

error[E0046]: not all trait items implemented, missing: `call_mut`
  --> /tmp/icemaker_global_tempdir.u1pxKPNyM6gY/rustc_testrunner_tmpdir_reporting.NfvSAW9e4CZU/mvce.rs:12:1
   |
12 | impl<T: Copy> FnMut<()> for Foo<T> {}
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ missing `call_mut` in implementation
   |
   = help: implement the missing item: `fn call_mut(&mut self, _: ()) -> <Self as FnOnce<()>>::Output { todo!() }`

error[E0053]: method `call_once` has an incompatible type for trait
  --> /tmp/icemaker_global_tempdir.u1pxKPNyM6gY/rustc_testrunner_tmpdir_reporting.NfvSAW9e4CZU/mvce.rs:17:5
   |
17 |     fn call_once(self, _: ()) -> T {
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected "rust-call" fn, found "Rust" fn
   |
   = note: expected signature `extern "rust-call" fn(Foo<_>, ()) -> _`
              found signature `fn(Foo<_>, ()) -> _`

thread 'rustc' panicked at /rustc/9aa232ecc7bb006a1fad404f437b049482021a3a/compiler/rustc_middle/src/mir/tcx.rs:133:61:
index out of bounds: the len is 6 but the index is 6
stack backtrace:
   0:     0x7f87783e2416 - std::backtrace_rs::backtrace::libunwind::trace::haa332446d2816da1
                               at /rustc/9aa232ecc7bb006a1fad404f437b049482021a3a/library/std/src/../../backtrace/src/backtrace/libunwind.rs:104:5
   1:     0x7f87783e2416 - std::backtrace_rs::backtrace::trace_unsynchronized::hc79ac4bb87de99b7
                               at /rustc/9aa232ecc7bb006a1fad404f437b049482021a3a/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f87783e2416 - std::sys_common::backtrace::_print_fmt::h826e31038d6fed55
                               at /rustc/9aa232ecc7bb006a1fad404f437b049482021a3a/library/std/src/sys_common/backtrace.rs:68:5
   3:     0x7f87783e2416 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h7d45101adaea8e2e
                               at /rustc/9aa232ecc7bb006a1fad404f437b049482021a3a/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7f8778434f90 - core::fmt::rt::Argument::fmt::habb091c2e565929c
                               at /rustc/9aa232ecc7bb006a1fad404f437b049482021a3a/library/core/src/fmt/rt.rs:142:9
   5:     0x7f8778434f90 - core::fmt::write::h430cd915198bfbfa
                               at /rustc/9aa232ecc7bb006a1fad404f437b049482021a3a/library/core/src/fmt/mod.rs:1120:17
   6:     0x7f87783d5c9f - std::io::Write::write_fmt::h76a4f85596572687
                               at /rustc/9aa232ecc7bb006a1fad404f437b049482021a3a/library/std/src/io/mod.rs:1854:15
   7:     0x7f87783e21f4 - std::sys_common::backtrace::_print::h730103227e62d0c1
                               at /rustc/9aa232ecc7bb006a1fad404f437b049482021a3a/library/std/src/sys_common/backtrace.rs:47:5
   8:     0x7f87783e21f4 - std::sys_common::backtrace::print::h4b37a0052f447bb6
                               at /rustc/9aa232ecc7bb006a1fad404f437b049482021a3a/library/std/src/sys_common/backtrace.rs:34:9
   9:     0x7f87783e4fe7 - std::panicking::default_hook::{{closure}}::h9ce01cf4995c297e
  10:     0x7f87783e4d49 - std::panicking::default_hook::h82708ac75720d681
                               at /rustc/9aa232ecc7bb006a1fad404f437b049482021a3a/library/std/src/panicking.rs:292:9
  11:     0x7f877514999c - std[2504e1f5e79dbd0a]::panicking::update_hook::<alloc[4e175fcaaf6bf4c3]::boxed::Box<rustc_driver_impl[f5849ce36d1a60d2]::install_ice_hook::{closure#0}>>::{closure#0}
  12:     0x7f87783e5736 - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::h9c044ab60f052747
                               at /rustc/9aa232ecc7bb006a1fad404f437b049482021a3a/library/alloc/src/boxed.rs:2030:9
  13:     0x7f87783e5736 - std::panicking::rust_panic_with_hook::h47b07230e93314a2
                               at /rustc/9aa232ecc7bb006a1fad404f437b049482021a3a/library/std/src/panicking.rs:785:13
  14:     0x7f87783e5482 - std::panicking::begin_panic_handler::{{closure}}::h6c5fbc890ce207d0
                               at /rustc/9aa232ecc7bb006a1fad404f437b049482021a3a/library/std/src/panicking.rs:659:13
  15:     0x7f87783e2916 - std::sys_common::backtrace::__rust_end_short_backtrace::hec2f82c01fee32cd
                               at /rustc/9aa232ecc7bb006a1fad404f437b049482021a3a/library/std/src/sys_common/backtrace.rs:171:18
  16:     0x7f87783e51d4 - rust_begin_unwind
                               at /rustc/9aa232ecc7bb006a1fad404f437b049482021a3a/library/std/src/panicking.rs:647:5
  17:     0x7f87784316e5 - core::panicking::panic_fmt::h48a1a0d3500755c9
                               at /rustc/9aa232ecc7bb006a1fad404f437b049482021a3a/library/core/src/panicking.rs:72:14
  18:     0x7f8778431932 - core::panicking::panic_bounds_check::h9c1f082d9b7cb73f
                               at /rustc/9aa232ecc7bb006a1fad404f437b049482021a3a/library/core/src/panicking.rs:208:5
  19:     0x7f8776def5d5 - rustc_const_eval[1987f47b2cdff49e]::transform::validate::validate_types
  20:     0x7f8776b8c65f - <rustc_const_eval[1987f47b2cdff49e]::transform::validate::Validator as rustc_middle[dddd7df0b25e8df]::mir::MirPass>::run_pass
  21:     0x7f8776410bf9 - rustc_mir_transform[156c0abd78acfd74]::pass_manager::run_passes_inner
  22:     0x7f877692882a - rustc_mir_transform[156c0abd78acfd74]::optimized_mir
  23:     0x7f877647a535 - rustc_query_impl[6d1f17dd37feccf6]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[6d1f17dd37feccf6]::query_impl::optimized_mir::dynamic_query::{closure#2}::{closure#0}, rustc_middle[dddd7df0b25e8df]::query::erase::Erased<[u8; 8usize]>>
  24:     0x7f877647abe1 - rustc_query_system[e40b0ad2841d92dc]::query::plumbing::try_execute_query::<rustc_query_impl[6d1f17dd37feccf6]::DynamicConfig<rustc_query_system[e40b0ad2841d92dc]::query::caches::DefIdCache<rustc_middle[dddd7df0b25e8df]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[6d1f17dd37feccf6]::plumbing::QueryCtxt, false>
  25:     0x7f877647a35e - rustc_query_impl[6d1f17dd37feccf6]::query_impl::optimized_mir::get_query_non_incr::__rust_end_short_backtrace
  26:     0x7f87767b3d9b - rustc_middle[dddd7df0b25e8df]::query::plumbing::query_get_at::<rustc_query_system[e40b0ad2841d92dc]::query::caches::DefIdCache<rustc_middle[dddd7df0b25e8df]::query::erase::Erased<[u8; 8usize]>>>
  27:     0x7f8776e1dba4 - rustc_query_impl[6d1f17dd37feccf6]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[6d1f17dd37feccf6]::query_impl::unused_generic_params::dynamic_query::{closure#2}::{closure#0}, rustc_middle[dddd7df0b25e8df]::query::erase::Erased<[u8; 4usize]>>
  28:     0x7f8776e1d36e - rustc_query_system[e40b0ad2841d92dc]::query::plumbing::try_execute_query::<rustc_query_impl[6d1f17dd37feccf6]::DynamicConfig<rustc_query_system[e40b0ad2841d92dc]::query::caches::DefaultCache<rustc_middle[dddd7df0b25e8df]::ty::instance::InstanceDef, rustc_middle[dddd7df0b25e8df]::query::erase::Erased<[u8; 4usize]>>, false, false, false>, rustc_query_impl[6d1f17dd37feccf6]::plumbing::QueryCtxt, false>
  29:     0x7f8776e1d052 - rustc_query_impl[6d1f17dd37feccf6]::query_impl::unused_generic_params::get_query_non_incr::__rust_end_short_backtrace
  30:     0x7f8776e18cf8 - rustc_interface[614167ae26197186]::passes::analysis
  31:     0x7f8776e182df - rustc_query_impl[6d1f17dd37feccf6]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[6d1f17dd37feccf6]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[dddd7df0b25e8df]::query::erase::Erased<[u8; 1usize]>>
  32:     0x7f8776ed2d64 - rustc_query_system[e40b0ad2841d92dc]::query::plumbing::try_execute_query::<rustc_query_impl[6d1f17dd37feccf6]::DynamicConfig<rustc_query_system[e40b0ad2841d92dc]::query::caches::SingleCache<rustc_middle[dddd7df0b25e8df]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[6d1f17dd37feccf6]::plumbing::QueryCtxt, false>
  33:     0x7f8776ed2ac7 - rustc_query_impl[6d1f17dd37feccf6]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  34:     0x7f877713006f - rustc_interface[614167ae26197186]::interface::run_compiler::<core[ae955e53bd86118a]::result::Result<(), rustc_span[5816d1300c2c104a]::ErrorGuaranteed>, rustc_driver_impl[f5849ce36d1a60d2]::run_compiler::{closure#0}>::{closure#0}
  35:     0x7f877736e0d2 - std[2504e1f5e79dbd0a]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[614167ae26197186]::util::run_in_thread_with_globals<rustc_interface[614167ae26197186]::util::run_in_thread_pool_with_globals<rustc_interface[614167ae26197186]::interface::run_compiler<core[ae955e53bd86118a]::result::Result<(), rustc_span[5816d1300c2c104a]::ErrorGuaranteed>, rustc_driver_impl[f5849ce36d1a60d2]::run_compiler::{closure#0}>::{closure#0}, core[ae955e53bd86118a]::result::Result<(), rustc_span[5816d1300c2c104a]::ErrorGuaranteed>>::{closure#0}, core[ae955e53bd86118a]::result::Result<(), rustc_span[5816d1300c2c104a]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[ae955e53bd86118a]::result::Result<(), rustc_span[5816d1300c2c104a]::ErrorGuaranteed>>
  36:     0x7f877736defe - <<std[2504e1f5e79dbd0a]::thread::Builder>::spawn_unchecked_<rustc_interface[614167ae26197186]::util::run_in_thread_with_globals<rustc_interface[614167ae26197186]::util::run_in_thread_pool_with_globals<rustc_interface[614167ae26197186]::interface::run_compiler<core[ae955e53bd86118a]::result::Result<(), rustc_span[5816d1300c2c104a]::ErrorGuaranteed>, rustc_driver_impl[f5849ce36d1a60d2]::run_compiler::{closure#0}>::{closure#0}, core[ae955e53bd86118a]::result::Result<(), rustc_span[5816d1300c2c104a]::ErrorGuaranteed>>::{closure#0}, core[ae955e53bd86118a]::result::Result<(), rustc_span[5816d1300c2c104a]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[ae955e53bd86118a]::result::Result<(), rustc_span[5816d1300c2c104a]::ErrorGuaranteed>>::{closure#1} as core[ae955e53bd86118a]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  37:     0x7f87783ee925 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h3205da42e967968e
                               at /rustc/9aa232ecc7bb006a1fad404f437b049482021a3a/library/alloc/src/boxed.rs:2016:9
  38:     0x7f87783ee925 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h3a8d804b35a578bc
                               at /rustc/9aa232ecc7bb006a1fad404f437b049482021a3a/library/alloc/src/boxed.rs:2016:9
  39:     0x7f87783ee925 - std::sys::pal::unix::thread::Thread::new::thread_start::ha87a0836a03cdbad
                               at /rustc/9aa232ecc7bb006a1fad404f437b049482021a3a/library/std/src/sys/pal/unix/thread.rs:108:17
  40:     0x7f87722aa9eb - <unknown>
  41:     0x7f877232e7cc - <unknown>
  42:                0x0 - <unknown>

error: the compiler unexpectedly panicked. this is a bug.

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 1.78.0-nightly (9aa232ecc 2024-02-11) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z mir-opt-level=0 -Z polymorphize=on -Z inline-mir=yes -Z dump-mir-dir=dir

query stack during panic:
#0 [optimized_mir] optimizing MIR for `<impl at /tmp/icemaker_global_tempdir.u1pxKPNyM6gY/rustc_testrunner_tmpdir_reporting.NfvSAW9e4CZU/mvce.rs:14:1: 14:36>::call_once`
#1 [unused_generic_params] determining which generic parameters are unused by `<impl at /tmp/icemaker_global_tempdir.u1pxKPNyM6gY/rustc_testrunner_tmpdir_reporting.NfvSAW9e4CZU/mvce.rs:14:1: 14:36>::call_once`
#2 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to 4 previous errors

Some errors have detailed explanations: E0046, E0053, E0601.
For more information about an error, try `rustc --explain E0046`.

[matthiaskrgr]

#120550 cc @oli-obk