Compiler panic related to const generics: "unexpected inference"

[tmerr]

Compiler panic on rustc 1.63.0-nightly (bb8c2f4 2022-06-19) running on x86_64-unknown-linux-gnu
I've only seen it happen when the function g does not exist.
In my original code that was the only problem (after reducing it to a smaller example the code is more broken, but the panic is the same).

-->

Code

struct S<const K: usize> {
    xs: Vec<[u8; K]>,
}

impl<const K: usize> S<K> {
    fn f(&self, a: [u8; K], cs: i32) -> S<K> {
        g(a).map(|ws| S{xs: ws.to_vec()})
    }
}

fn main() {}

Meta

rustc --version --verbose:

rustc 1.63.0-nightly (bb8c2f411 2022-06-19)
binary: rustc
commit-hash: bb8c2f41174caceec00c28bc6c5c20ae9f9a175c
commit-date: 2022-06-19
host: x86_64-unknown-linux-gnu
release: 1.63.0-nightly
LLVM version: 14.0.5

Error output

error[E0425]: cannot find function `g` in this scope
 --> main.rs:7:9
  |
5 | impl<const K: usize> S<K> {
  |            - similarly named const parameter `K` defined here
6 |     fn f(&self, a: [u8; K], cs: i32) -> S<K> {
7 |         g(a).map(|ws| S{xs: ws.to_vec()})
  |         ^ help: a const parameter with a similar name exists: `K`

error: internal compiler error: /rustc/bb8c2f41174caceec00c28bc6c5c20ae9f9a175c/compiler/rustc_infer/src/infer/nll_relate/mod.rs:665:17: unexpected inference var Const { ty: usize, kind: Infer(Var(_#0c)) }

thread 'rustc' panicked at 'Box<dyn Any>', /rustc/bb8c2f41174caceec00c28bc6c5c20ae9f9a175c/compiler/rustc_errors/src/lib.rs:1391:9
stack backtrace:
   0:     0x7f14678efe8d - std::backtrace_rs::backtrace::libunwind::trace::h7401910188046071
                               at /rustc/bb8c2f41174caceec00c28bc6c5c20ae9f9a175c/library/std/src/../../backtrace/src/backtrace/libunwind.rs:93:5
   1:     0x7f14678efe8d - std::backtrace_rs::backtrace::trace_unsynchronized::h8dff7aa2924f24e9
                               at /rustc/bb8c2f41174caceec00c28bc6c5c20ae9f9a175c/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7f14678efe8d - std::sys_common::backtrace::_print_fmt::h07ca90b544a24df2
                               at /rustc/bb8c2f41174caceec00c28bc6c5c20ae9f9a175c/library/std/src/sys_common/backtrace.rs:66:5
   3:     0x7f14678efe8d - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h9331308a3088c05f
                               at /rustc/bb8c2f41174caceec00c28bc6c5c20ae9f9a175c/library/std/src/sys_common/backtrace.rs:45:22
   4:     0x7f146794bc4c - core::fmt::write::h61c349b2e024d424
                               at /rustc/bb8c2f41174caceec00c28bc6c5c20ae9f9a175c/library/core/src/fmt/mod.rs:1196:17
   5:     0x7f14678e15b1 - std::io::Write::write_fmt::h84ca4b318d095fa7
                               at /rustc/bb8c2f41174caceec00c28bc6c5c20ae9f9a175c/library/std/src/io/mod.rs:1654:15
   6:     0x7f14678f2b55 - std::sys_common::backtrace::_print::hd3c72b1e40e79baf
                               at /rustc/bb8c2f41174caceec00c28bc6c5c20ae9f9a175c/library/std/src/sys_common/backtrace.rs:48:5
   7:     0x7f14678f2b55 - std::sys_common::backtrace::print::ha4da5a270383a62c
                               at /rustc/bb8c2f41174caceec00c28bc6c5c20ae9f9a175c/library/std/src/sys_common/backtrace.rs:35:9
   8:     0x7f14678f2b55 - std::panicking::default_hook::{{closure}}::h8c6cca5f381817ba
                               at /rustc/bb8c2f41174caceec00c28bc6c5c20ae9f9a175c/library/std/src/panicking.rs:295:22
   9:     0x7f14678f2876 - std::panicking::default_hook::he91089be4e889ce2
                               at /rustc/bb8c2f41174caceec00c28bc6c5c20ae9f9a175c/library/std/src/panicking.rs:314:9
  10:     0x7f14680cb464 - rustc_driver[3c4ddaa230521172]::DEFAULT_HOOK::{closure#0}::{closure#0}
  11:     0x7f14678f322a - std::panicking::rust_panic_with_hook::he7ddebf187262887
                               at /rustc/bb8c2f41174caceec00c28bc6c5c20ae9f9a175c/library/std/src/panicking.rs:702:17
  12:     0x7f1469188d11 - std[92178b8fea183b1]::panicking::begin_panic::<rustc_errors[bc32936de75f68a8]::ExplicitBug>::{closure#0}
  13:     0x7f1469187b36 - std[92178b8fea183b1]::sys_common::backtrace::__rust_end_short_backtrace::<std[92178b8fea183b1]::panicking::begin_panic<rustc_errors[bc32936de75f68a8]::ExplicitBug>::{closure#0}, !>
  14:     0x7f14690f42a6 - std[92178b8fea183b1]::panicking::begin_panic::<rustc_errors[bc32936de75f68a8]::ExplicitBug>
  15:     0x7f1469113a66 - std[92178b8fea183b1]::panic::panic_any::<rustc_errors[bc32936de75f68a8]::ExplicitBug>
  16:     0x7f1469111505 - <rustc_errors[bc32936de75f68a8]::HandlerInner>::bug::<&alloc[9a1da603931b4913]::string::String>
  17:     0x7f1469111260 - <rustc_errors[bc32936de75f68a8]::Handler>::bug::<&alloc[9a1da603931b4913]::string::String>
  18:     0x7f146918f6bd - rustc_middle[5e1b60369bd5df6]::ty::context::tls::with_opt::<rustc_middle[5e1b60369bd5df6]::util::bug::opt_span_bug_fmt<rustc_span[c6162a597843e319]::span_encoding::Span>::{closure#0}, ()>
  19:     0x7f146918f816 - rustc_middle[5e1b60369bd5df6]::util::bug::opt_span_bug_fmt::<rustc_span[c6162a597843e319]::span_encoding::Span>
  20:     0x7f146918f793 - rustc_middle[5e1b60369bd5df6]::util::bug::bug_fmt
  21:     0x7f146846111d - <rustc_infer[2986cd19b18a3338]::infer::nll_relate::TypeRelating<rustc_infer[2986cd19b18a3338]::infer::canonical::query_response::QueryTypeRelatingDelegate> as rustc_middle[5e1b60369bd5df6]::ty::relate::TypeRelation>::consts
  22:     0x7f146847fa0a - <rustc_infer[2986cd19b18a3338]::infer::InferCtxt>::instantiate_nll_query_response_and_region_obligations::<alloc[9a1da603931b4913]::vec::Vec<rustc_middle[5e1b60369bd5df6]::traits::query::OutlivesBound>>
  23:     0x7f14696b40ce - <rustc_infer[2986cd19b18a3338]::infer::outlives::env::OutlivesEnvironment as rustc_typeck[c4240235affd9ba6]::check::regionck::OutlivesEnvironmentExt>::add_implied_bounds
  24:     0x7f146976d821 - <rustc_typeck[c4240235affd9ba6]::check::regionck::RegionCtxt>::visit_fn_body
  25:     0x7f14697715d7 - <rustc_typeck[c4240235affd9ba6]::check::regionck::RegionCtxt as rustc_hir[6e5206eda1c7a30]::intravisit::Visitor>::visit_expr
  26:     0x7f146977015c - <rustc_typeck[c4240235affd9ba6]::check::regionck::RegionCtxt as rustc_hir[6e5206eda1c7a30]::intravisit::Visitor>::visit_expr
  27:     0x7f146977011c - <rustc_typeck[c4240235affd9ba6]::check::regionck::RegionCtxt as rustc_hir[6e5206eda1c7a30]::intravisit::Visitor>::visit_expr
  28:     0x7f146976dbce - <rustc_typeck[c4240235affd9ba6]::check::regionck::RegionCtxt>::visit_fn_body
  29:     0x7f146972cae9 - <rustc_infer[2986cd19b18a3338]::infer::InferCtxtBuilder>::enter::<&rustc_middle[5e1b60369bd5df6]::ty::context::TypeckResults, <rustc_typeck[c4240235affd9ba6]::check::inherited::InheritedBuilder>::enter<rustc_typeck[c4240235affd9ba6]::check::typeck_with_fallback<rustc_typeck[c4240235affd9ba6]::check::typeck::{closure#0}>::{closure#1}, &rustc_middle[5e1b60369bd5df6]::ty::context::TypeckResults>::{closure#0}>
  30:     0x7f14696c4a9a - rustc_typeck[c4240235affd9ba6]::check::typeck
  31:     0x7f1469c764b4 - rustc_query_system[e060dcc8c6e4714f]::query::plumbing::try_execute_query::<rustc_query_impl[85c2181340255b16]::plumbing::QueryCtxt, rustc_query_system[e060dcc8c6e4714f]::query::caches::DefaultCache<rustc_span[c6162a597843e319]::def_id::LocalDefId, &rustc_middle[5e1b60369bd5df6]::ty::context::TypeckResults>>
  32:     0x7f1469c4c7ee - <rustc_query_impl[85c2181340255b16]::Queries as rustc_middle[5e1b60369bd5df6]::ty::query::QueryEngine>::typeck
  33:     0x7f14696c4c2f - rustc_typeck[c4240235affd9ba6]::check::typeck
  34:     0x7f1469c764b4 - rustc_query_system[e060dcc8c6e4714f]::query::plumbing::try_execute_query::<rustc_query_impl[85c2181340255b16]::plumbing::QueryCtxt, rustc_query_system[e060dcc8c6e4714f]::query::caches::DefaultCache<rustc_span[c6162a597843e319]::def_id::LocalDefId, &rustc_middle[5e1b60369bd5df6]::ty::context::TypeckResults>>
  35:     0x7f1469c4c7ee - <rustc_query_impl[85c2181340255b16]::Queries as rustc_middle[5e1b60369bd5df6]::ty::query::QueryEngine>::typeck
  36:     0x7f1469786108 - <rustc_middle[5e1b60369bd5df6]::hir::map::Map>::par_body_owners::<rustc_typeck[c4240235affd9ba6]::check::typeck_item_bodies::{closure#0}>
  37:     0x7f146a52242c - rustc_typeck[c4240235affd9ba6]::check::typeck_item_bodies
  38:     0x7f146a81c2ec - rustc_query_system[e060dcc8c6e4714f]::query::plumbing::try_execute_query::<rustc_query_impl[85c2181340255b16]::plumbing::QueryCtxt, rustc_query_system[e060dcc8c6e4714f]::query::caches::DefaultCache<(), ()>>
  39:     0x7f146a848da1 - rustc_query_system[e060dcc8c6e4714f]::query::plumbing::get_query::<rustc_query_impl[85c2181340255b16]::queries::typeck_item_bodies, rustc_query_impl[85c2181340255b16]::plumbing::QueryCtxt>
  40:     0x7f146a561c63 - <rustc_session[52ecc3f9ef8fdbdb]::session::Session>::time::<(), rustc_typeck[c4240235affd9ba6]::check_crate::{closure#7}>
  41:     0x7f146a53d6f3 - rustc_typeck[c4240235affd9ba6]::check_crate
  42:     0x7f146a2ade47 - rustc_interface[5a583bacec404f39]::passes::analysis
  43:     0x7f146a81181f - rustc_query_system[e060dcc8c6e4714f]::query::plumbing::try_execute_query::<rustc_query_impl[85c2181340255b16]::plumbing::QueryCtxt, rustc_query_system[e060dcc8c6e4714f]::query::caches::DefaultCache<(), core[fd7ff14c59d02930]::result::Result<(), rustc_errors[bc32936de75f68a8]::ErrorGuaranteed>>>
  44:     0x7f146a85b2fe - rustc_query_system[e060dcc8c6e4714f]::query::plumbing::get_query::<rustc_query_impl[85c2181340255b16]::queries::analysis, rustc_query_impl[85c2181340255b16]::plumbing::QueryCtxt>
  45:     0x7f146a290f67 - <rustc_interface[5a583bacec404f39]::passes::QueryContext>::enter::<rustc_driver[3c4ddaa230521172]::run_compiler::{closure#1}::{closure#2}::{closure#3}, core[fd7ff14c59d02930]::result::Result<(), rustc_errors[bc32936de75f68a8]::ErrorGuaranteed>>
  46:     0x7f146a27b24f - <rustc_interface[5a583bacec404f39]::interface::Compiler>::enter::<rustc_driver[3c4ddaa230521172]::run_compiler::{closure#1}::{closure#2}, core[fd7ff14c59d02930]::result::Result<core[fd7ff14c59d02930]::option::Option<rustc_interface[5a583bacec404f39]::queries::Linker>, rustc_errors[bc32936de75f68a8]::ErrorGuaranteed>>
  47:     0x7f146a29f65f - rustc_span[c6162a597843e319]::with_source_map::<core[fd7ff14c59d02930]::result::Result<(), rustc_errors[bc32936de75f68a8]::ErrorGuaranteed>, rustc_interface[5a583bacec404f39]::interface::create_compiler_and_run<core[fd7ff14c59d02930]::result::Result<(), rustc_errors[bc32936de75f68a8]::ErrorGuaranteed>, rustc_driver[3c4ddaa230521172]::run_compiler::{closure#1}>::{closure#1}>
  48:     0x7f146a27c0e2 - <scoped_tls[df47f77656bf316c]::ScopedKey<rustc_span[c6162a597843e319]::SessionGlobals>>::set::<rustc_interface[5a583bacec404f39]::interface::run_compiler<core[fd7ff14c59d02930]::result::Result<(), rustc_errors[bc32936de75f68a8]::ErrorGuaranteed>, rustc_driver[3c4ddaa230521172]::run_compiler::{closure#1}>::{closure#0}, core[fd7ff14c59d02930]::result::Result<(), rustc_errors[bc32936de75f68a8]::ErrorGuaranteed>>
  49:     0x7f146a2915ef - std[92178b8fea183b1]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[5a583bacec404f39]::util::run_in_thread_pool_with_globals<rustc_interface[5a583bacec404f39]::interface::run_compiler<core[fd7ff14c59d02930]::result::Result<(), rustc_errors[bc32936de75f68a8]::ErrorGuaranteed>, rustc_driver[3c4ddaa230521172]::run_compiler::{closure#1}>::{closure#0}, core[fd7ff14c59d02930]::result::Result<(), rustc_errors[bc32936de75f68a8]::ErrorGuaranteed>>::{closure#0}, core[fd7ff14c59d02930]::result::Result<(), rustc_errors[bc32936de75f68a8]::ErrorGuaranteed>>
  50:     0x7f146a2917d9 - <<std[92178b8fea183b1]::thread::Builder>::spawn_unchecked_<rustc_interface[5a583bacec404f39]::util::run_in_thread_pool_with_globals<rustc_interface[5a583bacec404f39]::interface::run_compiler<core[fd7ff14c59d02930]::result::Result<(), rustc_errors[bc32936de75f68a8]::ErrorGuaranteed>, rustc_driver[3c4ddaa230521172]::run_compiler::{closure#1}>::{closure#0}, core[fd7ff14c59d02930]::result::Result<(), rustc_errors[bc32936de75f68a8]::ErrorGuaranteed>>::{closure#0}, core[fd7ff14c59d02930]::result::Result<(), rustc_errors[bc32936de75f68a8]::ErrorGuaranteed>>::{closure#1} as core[fd7ff14c59d02930]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  51:     0x7f14678fd163 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hd06934b23a7f2fcd
                               at /rustc/bb8c2f41174caceec00c28bc6c5c20ae9f9a175c/library/alloc/src/boxed.rs:1951:9
  52:     0x7f14678fd163 - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hb092aa1c4d31e227
                               at /rustc/bb8c2f41174caceec00c28bc6c5c20ae9f9a175c/library/alloc/src/boxed.rs:1951:9
  53:     0x7f14678fd163 - std::sys::unix::thread::Thread::new::thread_start::hea70d8d092b89098
                               at /rustc/bb8c2f41174caceec00c28bc6c5c20ae9f9a175c/library/std/src/sys/unix/thread.rs:108:17
  54:     0x7f14677ef259 - start_thread
  55:     0x7f14677165e3 - __GI___clone
  56:                0x0 - <unknown>

note: 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 1.63.0-nightly (bb8c2f411 2022-06-19) running on x86_64-unknown-linux-gnu

query stack during panic:
#0 [typeck] type-checking `<impl at main.rs:5:1: 9:2>::f`
#1 [typeck] type-checking `<impl at main.rs:5:1: 9:2>::f::{closure#0}`
#2 [typeck_item_bodies] type-checking all item bodies
#3 [analysis] running analysis passes on this crate
end of query stack
error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0425`.

[JohnTitor]

I think it's a duplicate of #98299.

[LoganDark]

I think it's a duplicate of #98299.

It's not.

I just ran into this issue myself and a repro (on linux) has been preserved here. No black_box to be found anywhere.

Once the code was fixed up to compile, the ICE went away.

rustc.stderr.txt

edit: It seems the root cause is the same. The latest nightly no longer ICEs (I was 1 nightly out of date).

[JohnTitor]

@LoganDark Note that the ICE doesn't need the black_box feature as it existed on the diagnostics.