ICE: tcx: `index out of bounds: the len is 1 but the index is 1`

[matthiaskrgr]

auto-reduced (treereduce-rust):

#![feature(specialization)]

pub trait Foo {
    fn abc() -> u32;
}

pub trait Marker {}

impl<T> Foo for T {
    default fn abc(f: fn(&T), t: &T) -> u32 {
        16
    }
}

impl<T: Marker> Foo for T {
    fn def() -> u32 {
        Self::abc()
    }
}

original:

// run-pass
#![feature(specialization)]
//~^ WARN the feature `specialization` is incomplete

pub trait Foo {
    fn abc() -> u32;
    fn def() -> u32;
}

pub trait Marker {}

impl Marker for () {}

impl<T> Foo for T {
    default fn abc(f: fn(&T), t: &T) -> u32 { 16 }
    default fn def() -> u32 { 42 }
}

impl<T: Marker> Foo for T {
    fn def() -> u32 {
        Self::abc()
    }
}

fn main() {
   assert_eq!(<()>::def(), 16);
   assert_eq!(<i32>::def(), 42);
}

Version information

rustc 1.78.0-nightly (ee9c7c940 2024-02-14)
binary: rustc
commit-hash: ee9c7c940c07d8b67c9a6b2ec930db70dcd23a46
commit-date: 2024-02-14
host: x86_64-unknown-linux-gnu
release: 1.78.0-nightly
LLVM version: 18.1.0

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

Program output

error[E0407]: method `def` is not a member of trait `Foo`
  --> /tmp/icemaker_global_tempdir.M7q9vo4k970Y/rustc_testrunner_tmpdir_reporting.QyBQD8LaDYVe/mvce.rs:16:5
   |
16 | /     fn def() -> u32 {
17 | |         Self::abc()
18 | |     }
   | |_____^ not a member of trait `Foo`

warning: the feature `specialization` is incomplete and may not be safe to use and/or cause compiler crashes
 --> /tmp/icemaker_global_tempdir.M7q9vo4k970Y/rustc_testrunner_tmpdir_reporting.QyBQD8LaDYVe/mvce.rs:1:12
  |
1 | #![feature(specialization)]
  |            ^^^^^^^^^^^^^^
  |
  = note: see issue #31844 <https://github.com/rust-lang/rust/issues/31844> for more information
  = help: consider using `min_specialization` instead, which is more stable and complete
  = note: `#[warn(incomplete_features)]` on by default

error[E0601]: `main` function not found in crate `mvce`
  --> /tmp/icemaker_global_tempdir.M7q9vo4k970Y/rustc_testrunner_tmpdir_reporting.QyBQD8LaDYVe/mvce.rs:19:2
   |
19 | }
   |  ^ consider adding a `main` function to `/tmp/icemaker_global_tempdir.M7q9vo4k970Y/rustc_testrunner_tmpdir_reporting.QyBQD8LaDYVe/mvce.rs`

error[E0050]: method `abc` has 2 parameters but the declaration in trait `Foo::abc` has 0
  --> /tmp/icemaker_global_tempdir.M7q9vo4k970Y/rustc_testrunner_tmpdir_reporting.QyBQD8LaDYVe/mvce.rs:10:23
   |
4  |     fn abc() -> u32;
   |     ---------------- trait requires 0 parameters
...
10 |     default fn abc(f: fn(&T), t: &T) -> u32 {
   |                       ^^^^^^^^^^^^^ expected 0 parameters, found 2

warning: unused variable: `f`
  --> /tmp/icemaker_global_tempdir.M7q9vo4k970Y/rustc_testrunner_tmpdir_reporting.QyBQD8LaDYVe/mvce.rs:10:20
   |
10 |     default fn abc(f: fn(&T), t: &T) -> u32 {
   |                    ^ help: if this is intentional, prefix it with an underscore: `_f`
   |
   = note: `#[warn(unused_variables)]` on by default

warning: unused variable: `t`
  --> /tmp/icemaker_global_tempdir.M7q9vo4k970Y/rustc_testrunner_tmpdir_reporting.QyBQD8LaDYVe/mvce.rs:10:31
   |
10 |     default fn abc(f: fn(&T), t: &T) -> u32 {
   |                               ^ help: if this is intentional, prefix it with an underscore: `_t`

thread 'rustc' panicked at /rustc/ee9c7c940c07d8b67c9a6b2ec930db70dcd23a46/compiler/rustc_middle/src/mir/tcx.rs:133:61:
index out of bounds: the len is 1 but the index is 1
stack backtrace:
   0:     0x7f1870d8ce46 - std::backtrace_rs::backtrace::libunwind::trace::h5168cb64cb843b87
                               at /rustc/ee9c7c940c07d8b67c9a6b2ec930db70dcd23a46/library/std/src/../../backtrace/src/backtrace/libunwind.rs:104:5
   1:     0x7f1870d8ce46 - std::backtrace_rs::backtrace::trace_unsynchronized::hbbff473666b784c6
                               at /rustc/ee9c7c940c07d8b67c9a6b2ec930db70dcd23a46/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f1870d8ce46 - std::sys_common::backtrace::_print_fmt::h6c61b632e6cc7949
                               at /rustc/ee9c7c940c07d8b67c9a6b2ec930db70dcd23a46/library/std/src/sys_common/backtrace.rs:68:5
   3:     0x7f1870d8ce46 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h974a6b559c2b8d41
                               at /rustc/ee9c7c940c07d8b67c9a6b2ec930db70dcd23a46/library/std/src/sys_common/backtrace.rs:44:22
   4:     0x7f1870ddd46c - core::fmt::rt::Argument::fmt::hf6a5273aff56768c
                               at /rustc/ee9c7c940c07d8b67c9a6b2ec930db70dcd23a46/library/core/src/fmt/rt.rs:142:9
   5:     0x7f1870ddd46c - core::fmt::write::h1caffe3a78971207
                               at /rustc/ee9c7c940c07d8b67c9a6b2ec930db70dcd23a46/library/core/src/fmt/mod.rs:1120:17
   6:     0x7f1870d807ef - std::io::Write::write_fmt::h2caf2bb3485e27a5
                               at /rustc/ee9c7c940c07d8b67c9a6b2ec930db70dcd23a46/library/std/src/io/mod.rs:1854:15
   7:     0x7f1870d8cbf4 - std::sys_common::backtrace::_print::h0414d95b24b9ea44
                               at /rustc/ee9c7c940c07d8b67c9a6b2ec930db70dcd23a46/library/std/src/sys_common/backtrace.rs:47:5
   8:     0x7f1870d8cbf4 - std::sys_common::backtrace::print::hfdf60e3b3d06625d
                               at /rustc/ee9c7c940c07d8b67c9a6b2ec930db70dcd23a46/library/std/src/sys_common/backtrace.rs:34:9
   9:     0x7f1870d8f93b - std::panicking::default_hook::{{closure}}::h3c1109072cde0ade
  10:     0x7f1870d8f689 - std::panicking::default_hook::hfe3c076d4f24ecbe
                               at /rustc/ee9c7c940c07d8b67c9a6b2ec930db70dcd23a46/library/std/src/panicking.rs:292:9
  11:     0x7f1873bf563c - std[2308076c1424b998]::panicking::update_hook::<alloc[33ce0ef41c101337]::boxed::Box<rustc_driver_impl[d317596fd5f90102]::install_ice_hook::{closure#0}>>::{closure#0}
  12:     0x7f1870d900a0 - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::h8a55f98e23703736
                               at /rustc/ee9c7c940c07d8b67c9a6b2ec930db70dcd23a46/library/alloc/src/boxed.rs:2030:9
  13:     0x7f1870d900a0 - std::panicking::rust_panic_with_hook::hc147efcd5d482f2c
                               at /rustc/ee9c7c940c07d8b67c9a6b2ec930db70dcd23a46/library/std/src/panicking.rs:785:13
  14:     0x7f1870d8fde2 - std::panicking::begin_panic_handler::{{closure}}::h6174f0cd2a065d90
                               at /rustc/ee9c7c940c07d8b67c9a6b2ec930db70dcd23a46/library/std/src/panicking.rs:659:13
  15:     0x7f1870d8d326 - std::sys_common::backtrace::__rust_end_short_backtrace::h770b1c8f4d2029d4
                               at /rustc/ee9c7c940c07d8b67c9a6b2ec930db70dcd23a46/library/std/src/sys_common/backtrace.rs:171:18
  16:     0x7f1870d8fb14 - rust_begin_unwind
                               at /rustc/ee9c7c940c07d8b67c9a6b2ec930db70dcd23a46/library/std/src/panicking.rs:647:5
  17:     0x7f1870dd9975 - core::panicking::panic_fmt::h66e8ea0facb42563
                               at /rustc/ee9c7c940c07d8b67c9a6b2ec930db70dcd23a46/library/core/src/panicking.rs:72:14
  18:     0x7f1870dd9bc2 - core::panicking::panic_bounds_check::h178a976047dd7a3b
                               at /rustc/ee9c7c940c07d8b67c9a6b2ec930db70dcd23a46/library/core/src/panicking.rs:208:5
  19:     0x7f18730fc93a - <rustc_mir_transform[c0673d0b3c528a53]::remove_zsts::RemoveZsts as rustc_middle[efc8e2d5742a68dd]::mir::MirPass>::run_pass
  20:     0x7f1874e1420f - rustc_mir_transform[c0673d0b3c528a53]::pass_manager::run_passes_inner
  21:     0x7f1875157fbd - rustc_mir_transform[c0673d0b3c528a53]::optimized_mir
  22:     0x7f1874e92975 - rustc_query_impl[ecef4a4fa1cc3689]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[ecef4a4fa1cc3689]::query_impl::optimized_mir::dynamic_query::{closure#2}::{closure#0}, rustc_middle[efc8e2d5742a68dd]::query::erase::Erased<[u8; 8usize]>>
  23:     0x7f1874e93020 - rustc_query_system[8b26caae5283da17]::query::plumbing::try_execute_query::<rustc_query_impl[ecef4a4fa1cc3689]::DynamicConfig<rustc_query_system[8b26caae5283da17]::query::caches::DefIdCache<rustc_middle[efc8e2d5742a68dd]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[ecef4a4fa1cc3689]::plumbing::QueryCtxt, false>
  24:     0x7f1874e9279e - rustc_query_impl[ecef4a4fa1cc3689]::query_impl::optimized_mir::get_query_non_incr::__rust_end_short_backtrace
  25:     0x7f18757f01d8 - rustc_middle[efc8e2d5742a68dd]::query::plumbing::query_get_at::<rustc_query_system[8b26caae5283da17]::query::caches::DefIdCache<rustc_middle[efc8e2d5742a68dd]::query::erase::Erased<[u8; 8usize]>>>
  26:     0x7f1875800c32 - rustc_query_impl[ecef4a4fa1cc3689]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[ecef4a4fa1cc3689]::query_impl::unused_generic_params::dynamic_query::{closure#2}::{closure#0}, rustc_middle[efc8e2d5742a68dd]::query::erase::Erased<[u8; 4usize]>>
  27:     0x7f187580041b - rustc_query_system[8b26caae5283da17]::query::plumbing::try_execute_query::<rustc_query_impl[ecef4a4fa1cc3689]::DynamicConfig<rustc_query_system[8b26caae5283da17]::query::caches::DefaultCache<rustc_middle[efc8e2d5742a68dd]::ty::instance::InstanceDef, rustc_middle[efc8e2d5742a68dd]::query::erase::Erased<[u8; 4usize]>>, false, false, false>, rustc_query_impl[ecef4a4fa1cc3689]::plumbing::QueryCtxt, false>
  28:     0x7f187580012c - rustc_query_impl[ecef4a4fa1cc3689]::query_impl::unused_generic_params::get_query_non_incr::__rust_end_short_backtrace
  29:     0x7f18757fbc2c - rustc_interface[e88069c12facd435]::passes::analysis
  30:     0x7f18757fb229 - rustc_query_impl[ecef4a4fa1cc3689]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[ecef4a4fa1cc3689]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[efc8e2d5742a68dd]::query::erase::Erased<[u8; 1usize]>>
  31:     0x7f1875c3afe5 - rustc_query_system[8b26caae5283da17]::query::plumbing::try_execute_query::<rustc_query_impl[ecef4a4fa1cc3689]::DynamicConfig<rustc_query_system[8b26caae5283da17]::query::caches::SingleCache<rustc_middle[efc8e2d5742a68dd]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[ecef4a4fa1cc3689]::plumbing::QueryCtxt, false>
  32:     0x7f1875c3ad49 - rustc_query_impl[ecef4a4fa1cc3689]::query_impl::analysis::get_query_non_incr::__rust_end_short_backtrace
  33:     0x7f1875c44695 - rustc_interface[e88069c12facd435]::interface::run_compiler::<core[db7e23408f407db6]::result::Result<(), rustc_span[e043cedf16fd8748]::ErrorGuaranteed>, rustc_driver_impl[d317596fd5f90102]::run_compiler::{closure#0}>::{closure#0}
  34:     0x7f1875dc5ad8 - std[2308076c1424b998]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[e88069c12facd435]::util::run_in_thread_with_globals<rustc_interface[e88069c12facd435]::util::run_in_thread_pool_with_globals<rustc_interface[e88069c12facd435]::interface::run_compiler<core[db7e23408f407db6]::result::Result<(), rustc_span[e043cedf16fd8748]::ErrorGuaranteed>, rustc_driver_impl[d317596fd5f90102]::run_compiler::{closure#0}>::{closure#0}, core[db7e23408f407db6]::result::Result<(), rustc_span[e043cedf16fd8748]::ErrorGuaranteed>>::{closure#0}, core[db7e23408f407db6]::result::Result<(), rustc_span[e043cedf16fd8748]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[db7e23408f407db6]::result::Result<(), rustc_span[e043cedf16fd8748]::ErrorGuaranteed>>
  35:     0x7f1875dc5904 - <<std[2308076c1424b998]::thread::Builder>::spawn_unchecked_<rustc_interface[e88069c12facd435]::util::run_in_thread_with_globals<rustc_interface[e88069c12facd435]::util::run_in_thread_pool_with_globals<rustc_interface[e88069c12facd435]::interface::run_compiler<core[db7e23408f407db6]::result::Result<(), rustc_span[e043cedf16fd8748]::ErrorGuaranteed>, rustc_driver_impl[d317596fd5f90102]::run_compiler::{closure#0}>::{closure#0}, core[db7e23408f407db6]::result::Result<(), rustc_span[e043cedf16fd8748]::ErrorGuaranteed>>::{closure#0}, core[db7e23408f407db6]::result::Result<(), rustc_span[e043cedf16fd8748]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[db7e23408f407db6]::result::Result<(), rustc_span[e043cedf16fd8748]::ErrorGuaranteed>>::{closure#1} as core[db7e23408f407db6]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  36:     0x7f1870d991e5 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hbe12538a3d7e111d
                               at /rustc/ee9c7c940c07d8b67c9a6b2ec930db70dcd23a46/library/alloc/src/boxed.rs:2016:9
  37:     0x7f1870d991e5 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::h306728bac30291a0
                               at /rustc/ee9c7c940c07d8b67c9a6b2ec930db70dcd23a46/library/alloc/src/boxed.rs:2016:9
  38:     0x7f1870d991e5 - std::sys::pal::unix::thread::Thread::new::thread_start::hec142a176366d167
                               at /rustc/ee9c7c940c07d8b67c9a6b2ec930db70dcd23a46/library/std/src/sys/pal/unix/thread.rs:108:17
  39:     0x7f1870b809eb - <unknown>
  40:     0x7f1870c047cc - <unknown>
  41:                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 (ee9c7c940 2024-02-14) running on x86_64-unknown-linux-gnu

note: compiler flags: -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.M7q9vo4k970Y/rustc_testrunner_tmpdir_reporting.QyBQD8LaDYVe/mvce.rs:15:1: 15:26>::def`
#1 [unused_generic_params] determining which generic parameters are unused by `<impl at /tmp/icemaker_global_tempdir.M7q9vo4k970Y/rustc_testrunner_tmpdir_reporting.QyBQD8LaDYVe/mvce.rs:15:1: 15:26>::def`
#2 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to 3 previous errors; 3 warnings emitted

Some errors have detailed explanations: E0050, E0407, E0601.
For more information about an error, try `rustc --explain E0050`.

[matthiaskrgr]

#120550 cc @oli-obk