Repository: rust
Issue: ICE: impossible case reached wit gce + v0 symbol mangling
Labels: I-ICE,T-compiler,C-bug,F-generic_const_exprs,S-bug-has-test,requires-incomplete-features

<!--
[31mICE[0m: Rustc ./a.rs '-Cinstrument-coverage -ooutputfile -Zdump-mir-dir=dir' 'error: internal compiler error: compiler/rustc_symbol_mangling/src/v0.rs:578:42: impossible case reached', 'error: internal compiler error: compiler/rustc_symbol_mangling/src/v0.rs:578:42: impossible case reached'
File: /tmp/im/a.rs
-->

auto-reduced (treereduce-rust):
````rust
//@compile-flags: -Cinstrument-coverage
#![feature(generic_const_exprs)]
struct Inner<const N: usize, const M: usize>;
impl<const N: usize, const M: usize> Inner<N, M>
where
    [(); N + M]:,
{
    fn i() -> Self {
        Self
    }
}

struct Outer<const A: usize, const B: usize>(Inner<A, { B * 2 }>)
where
    [(); A + (B * 2)]:;
impl<const A: usize, const B: usize> Outer<A, B>
where
    [(); A + (B * 2)]:,
{
    fn o() -> Self {
        Self(Inner::i())
    }
}

fn main() {
    Outer::<1, 1>::o();
}

````

original:
````rust
#![allow(incomplete_features)]
#![feature(generic_const_exprs)]
struct Inner<const N: usize, const M: usize>;
impl<const N: usize, const M: usize> Inner<N, M> where [(); N + M]: {
    fn i() -> Self {
        Self
    }
}

struct Outer<const A: usize, const B: usize>(Inner<A, { B * 2 }>) where [(); A + (B * 2)]:;
impl<const A: usize, const B: usize> Outer<A, B> where [(); A + (B * 2)]: {
    fn o() -> Self {
        Self(Inner::i())
    }
}

fn main() {
    Outer::<1, 1>::o();
}

````

Version information
````
rustc 1.85.0-nightly (057bdb37e 2024-12-18)
binary: rustc
commit-hash: 057bdb37eccff6a2bd402509bbbadb9d73ad7bf5
commit-date: 2024-12-18
host: x86_64-unknown-linux-gnu
release: 1.85.0-nightly
LLVM version: 19.1.6

````

Possibly related line of code:
https://github.com/rust-lang/rust/blob/057bdb37eccff6a2bd402509bbbadb9d73ad7bf5/compiler/rustc_symbol_mangling/src/v0.rs#L572-L584

Command:
`/home/matthias/.rustup/toolchains/master/bin/rustc -Cinstrument-coverage`

<details><summary><strong>Program output</strong></summary>
<p>

```
warning: the feature `generic_const_exprs` is incomplete and may not be safe to use and/or cause compiler crashes
 --> /tmp/icemaker_global_tempdir.Vj5eJd7yWmCg/rustc_testrunner_tmpdir_reporting.hpXCYSBbyu42/mvce.rs:1:12
  |
1 | #![feature(generic_const_exprs)]
  |            ^^^^^^^^^^^^^^^^^^^
  |
  = note: see issue #76560 <https://github.com/rust-lang/rust/issues/76560> for more information
  = note: `#[warn(incomplete_features)]` on by default

error: internal compiler error: compiler/rustc_symbol_mangling/src/v0.rs:578:42: impossible case reached

thread 'rustc' panicked at compiler/rustc_symbol_mangling/src/v0.rs:578:42:
Box<dyn Any>
stack backtrace:
   0:     0x77006137164a - <std::sys::backtrace::BacktraceLock::print::DisplayBacktrace as core::fmt::Display>::fmt::he51ca9b0dc91b94e
   1:     0x770061a13dbc - core::fmt::write::h2fe894f1a71f3577
   2:     0x770062989091 - std::io::Write::write_fmt::h76ab228c5bf44dde
   3:     0x7700613714a2 - std::sys::backtrace::BacktraceLock::print::h54c62b0f13f3e5cd
   4:     0x77006137399a - std::panicking::default_hook::{{closure}}::hde230593691540bb
   5:     0x7700613737e3 - std::panicking::default_hook::h93566d26810460b4
   6:     0x7700604e01e8 - std[3b55a5d72aeb08a8]::panicking::update_hook::<alloc[33b8f9c30a0f5ec3]::boxed::Box<rustc_driver_impl[d048b04913314086]::install_ice_hook::{closure#0}>>::{closure#0}
   7:     0x770061374158 - std::panicking::rust_panic_with_hook::h8f04bfe0058df3f9
   8:     0x77006051ae71 - std[3b55a5d72aeb08a8]::panicking::begin_panic::<rustc_errors[84dd1c3e8f0c26d7]::ExplicitBug>::{closure#0}
   9:     0x770060510056 - std[3b55a5d72aeb08a8]::sys::backtrace::__rust_end_short_backtrace::<std[3b55a5d72aeb08a8]::panicking::begin_panic<rustc_errors[84dd1c3e8f0c26d7]::ExplicitBug>::{closure#0}, !>
  10:     0x77006050cc8d - std[3b55a5d72aeb08a8]::panicking::begin_panic::<rustc_errors[84dd1c3e8f0c26d7]::ExplicitBug>
  11:     0x770060524dd1 - <rustc_errors[84dd1c3e8f0c26d7]::diagnostic::BugAbort as rustc_errors[84dd1c3e8f0c26d7]::diagnostic::EmissionGuarantee>::emit_producing_guarantee
  12:     0x770060afb9d3 - rustc_middle[c5657185550747ed]::util::bug::opt_span_bug_fmt::<rustc_span[430234a91bb838ed]::span_encoding::Span>::{closure#0}
  13:     0x770060ae133a - rustc_middle[c5657185550747ed]::ty::context::tls::with_opt::<rustc_middle[c5657185550747ed]::util::bug::opt_span_bug_fmt<rustc_span[430234a91bb838ed]::span_encoding::Span>::{closure#0}, !>::{closure#0}
  14:     0x770060ae11cb - rustc_middle[c5657185550747ed]::ty::context::tls::with_context_opt::<rustc_middle[c5657185550747ed]::ty::context::tls::with_opt<rustc_middle[c5657185550747ed]::util::bug::opt_span_bug_fmt<rustc_span[430234a91bb838ed]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  15:     0x77005ebce5c0 - rustc_middle[c5657185550747ed]::util::bug::bug_fmt
  16:     0x77006105929f - <rustc_symbol_mangling[d2b91f94fa5b6f43]::v0::SymbolMangler as rustc_middle[c5657185550747ed]::ty::print::Printer>::print_const
  17:     0x77006105988a - <rustc_symbol_mangling[d2b91f94fa5b6f43]::v0::SymbolMangler as rustc_middle[c5657185550747ed]::ty::print::Printer>::path_generic_args::<<rustc_symbol_mangling[d2b91f94fa5b6f43]::v0::SymbolMangler as rustc_middle[c5657185550747ed]::ty::print::Printer>::default_print_def_path::{closure#3}>
  18:     0x770061057151 - <rustc_symbol_mangling[d2b91f94fa5b6f43]::v0::SymbolMangler as rustc_middle[c5657185550747ed]::ty::print::Printer>::print_def_path
  19:     0x770061057c4d - <rustc_symbol_mangling[d2b91f94fa5b6f43]::v0::SymbolMangler as rustc_middle[c5657185550747ed]::ty::print::Printer>::print_type
  20:     0x770061057365 - <rustc_symbol_mangling[d2b91f94fa5b6f43]::v0::SymbolMangler as rustc_middle[c5657185550747ed]::ty::print::Printer>::print_impl_path
  21:     0x7700610569e4 - <rustc_symbol_mangling[d2b91f94fa5b6f43]::v0::SymbolMangler as rustc_middle[c5657185550747ed]::ty::print::Printer>::print_def_path
  22:     0x7700610570e7 - <rustc_symbol_mangling[d2b91f94fa5b6f43]::v0::SymbolMangler as rustc_middle[c5657185550747ed]::ty::print::Printer>::print_def_path
  23:     0x770061056450 - rustc_symbol_mangling[d2b91f94fa5b6f43]::v0::mangle
  24:     0x7700620c6e5f - rustc_symbol_mangling[d2b91f94fa5b6f43]::symbol_name_provider
  25:     0x7700620c58ea - rustc_query_impl[7ef989d5bbee9c2]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[7ef989d5bbee9c2]::query_impl::symbol_name::dynamic_query::{closure#2}::{closure#0}, rustc_middle[c5657185550747ed]::query::erase::Erased<[u8; 16usize]>>
  26:     0x7700620c4877 - rustc_query_system[ccd0af510523da55]::query::plumbing::try_execute_query::<rustc_query_impl[7ef989d5bbee9c2]::DynamicConfig<rustc_query_system[ccd0af510523da55]::query::caches::DefaultCache<rustc_middle[c5657185550747ed]::ty::instance::Instance, rustc_middle[c5657185550747ed]::query::erase::Erased<[u8; 16usize]>>, false, false, false>, rustc_query_impl[7ef989d5bbee9c2]::plumbing::QueryCtxt, false>
  27:     0x7700620c44e2 - rustc_query_impl[7ef989d5bbee9c2]::query_impl::symbol_name::get_query_non_incr::__rust_end_short_backtrace
  28:     0x7700628254c2 - <rustc_middle[c5657185550747ed]::mir::mono::MonoItem>::symbol_name
  29:     0x770062824fbd - rustc_monomorphize[318401024c3aab57]::partitioning::assert_symbols_are_distinct::<core[d6142de48f57c781]::slice::iter::Iter<rustc_middle[c5657185550747ed]::mir::mono::MonoItem>>
  30:     0x7700620e17fd - rustc_monomorphize[318401024c3aab57]::partitioning::collect_and_partition_mono_items
  31:     0x7700620dfca4 - rustc_query_impl[7ef989d5bbee9c2]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[7ef989d5bbee9c2]::query_impl::collect_and_partition_mono_items::dynamic_query::{closure#2}::{closure#0}, rustc_middle[c5657185550747ed]::query::erase::Erased<[u8; 24usize]>>
  32:     0x7700620dfc89 - <rustc_query_impl[7ef989d5bbee9c2]::query_impl::collect_and_partition_mono_items::dynamic_query::{closure#2} as core[d6142de48f57c781]::ops::function::FnOnce<(rustc_middle[c5657185550747ed]::ty::context::TyCtxt, ())>>::call_once
  33:     0x7700629b0a20 - rustc_query_system[ccd0af510523da55]::query::plumbing::try_execute_query::<rustc_query_impl[7ef989d5bbee9c2]::DynamicConfig<rustc_query_system[ccd0af510523da55]::query::caches::SingleCache<rustc_middle[c5657185550747ed]::query::erase::Erased<[u8; 24usize]>>, false, false, false>, rustc_query_impl[7ef989d5bbee9c2]::plumbing::QueryCtxt, false>
  34:     0x7700629b0720 - rustc_query_impl[7ef989d5bbee9c2]::query_impl::collect_and_partition_mono_items::get_query_non_incr::__rust_end_short_backtrace
  35:     0x7700629f5630 - <rustc_codegen_llvm[642dbb4fc0deb88d]::LlvmCodegenBackend as rustc_codegen_ssa[f60ac56e662ca6db]::traits::backend::CodegenBackend>::codegen_crate
  36:     0x7700629e1c64 - <rustc_interface[f31e59266673035b]::queries::Linker>::codegen_and_build_linker
  37:     0x77006299b3d2 - rustc_interface[f31e59266673035b]::passes::create_and_enter_global_ctxt::<core[d6142de48f57c781]::option::Option<rustc_interface[f31e59266673035b]::queries::Linker>, rustc_driver_impl[d048b04913314086]::run_compiler::{closure#0}::{closure#2}>::{closure#2}::{closure#0}
  38:     0x770062a15b83 - rustc_interface[f31e59266673035b]::interface::run_compiler::<(), rustc_driver_impl[d048b04913314086]::run_compiler::{closure#0}>::{closure#1}
  39:     0x770062918511 - std[3b55a5d72aeb08a8]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[f31e59266673035b]::util::run_in_thread_with_globals<rustc_interface[f31e59266673035b]::util::run_in_thread_pool_with_globals<rustc_interface[f31e59266673035b]::interface::run_compiler<(), rustc_driver_impl[d048b04913314086]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  40:     0x7700629189a6 - <<std[3b55a5d72aeb08a8]::thread::Builder>::spawn_unchecked_<rustc_interface[f31e59266673035b]::util::run_in_thread_with_globals<rustc_interface[f31e59266673035b]::util::run_in_thread_pool_with_globals<rustc_interface[f31e59266673035b]::interface::run_compiler<(), rustc_driver_impl[d048b04913314086]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[d6142de48f57c781]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  41:     0x770062919f6f - std::sys::pal::unix::thread::Thread::new::thread_start::he7ac21643e42d931
  42:     0x77005cca339d - <unknown>
  43:     0x77005cd2849c - <unknown>
  44:                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 1.85.0-nightly (057bdb37e 2024-12-18) running on x86_64-unknown-linux-gnu

note: compiler flags: -C instrument-coverage -Z dump-mir-dir=dir

query stack during panic:
#0 [symbol_name] computing the symbol for `<impl at /tmp/icemaker_global_tempdir.Vj5eJd7yWmCg/rustc_testrunner_tmpdir_reporting.hpXCYSBbyu42/mvce.rs:3:1: 5:18>::i`
#1 [collect_and_partition_mono_items] collect_and_partition_mono_items
end of query stack
error: aborting due to 1 previous error; 1 warning emitted


```

</p>
</details>

<!--
query stack:
#0 [symbol_name] computing the symbol for `<impl at /tmp/icemaker_global_tempdir.Vj5eJd7yWmCg/rustc_testrunner_tmpdir_reporting.hpXCYSBbyu42/mvce.rs:3:1: 5:18>::i`
#1 [collect_and_partition_mono_items] collect_and_partition_mono_items

-->
@rustbot label +F-generic_const_exprs