ICE with const-generic enum pattern

[CraftSpider]

Code

enum ConstGenericEnum<const N: usize> {
    Foo([i32; N]),
    Bar,
}

fn foo<const N: usize>(val: &ConstGenericEnum<N>) {
    if let ConstGenericEnum::<N>::Foo(field, ..) = val {
        // Do stuff
    } else {
        // Do other stuff
    }
}

Note: The actual variant matched seems to be irrelevant, the significant part is the ::<N>. This does not need any feature flags, and adding either min_const_generics or const_generics does not fix it.

Meta

rustc --version --verbose:

rustc 1.51.0-nightly (158f8d034 2020-12-29)
binary: rustc
commit-hash: 158f8d034b15e65ba8dc0d066358dd0632bfcd6e
commit-date: 2020-12-29
host: x86_64-pc-windows-msvc
release: 1.51.0-nightly

Error output

error: internal compiler error: unexpected const parent in type_of_def_id(): Pat(Pat { hir_id: HirId { owner: DefId(0:11 ~ consts[4055]::foo), local_id: 15 }, kind: TupleStruct(Resolved(None, Path { span: src\main.rs:10:12: 10:38 (#0), res: Def(Ctor(Variant, Fn), DefId(0:6 ~ consts[4055]::ConstGenericEnum::Foo::{constructor#0})), segments: [PathSegment { ident: ConstGenericEnum#0, hir_id: Some(HirId { owner: DefId(0:11 ~ consts[4055]::foo), local_id: 12 }), res: Some(Def(Enum, DefId(0:3 ~ consts[4055]::ConstGenericEnum))), args: Some(GenericArgs { args: [Const(ConstArg { value: AnonConst { hir_id: HirId { owner: DefId(0:11 ~ consts[4055]::foo), local_id: 9 }, body: BodyId { hir_id: HirId { owner: DefId(0:11 ~ consts[4055]::foo), local_id: 11 } } }, span: src\main.rs:10:31: 10:32 (#0) })], bindings: [], parenthesized: false }), infer_args: false }, PathSegment { ident: Foo#0, hir_id: Some(HirId { owner: DefId(0:11 ~ consts[4055]::foo), local_id: 13 }), res: Some(Err), args: None, infer_args: true }] }), [Pat { hir_id: HirId { owner: DefId(0:11 ~ consts[4055]::foo), local_id: 14 }, kind: Binding(Unannotated, HirId { owner: DefId(0:11 ~ consts[4055]::foo), local_id: 14 }, field#0, None), span: src\main.rs:10:39: 10:44 (#0), default_binding_modes: true }], Some(1)), span: src\main.rs:10:12: 10:49 (#0), default_binding_modes: true })
  |
  = note: delayed at compiler\rustc_typeck\src\collect\type_of.rs:334:26


error: internal compiler error: TyKind::Error constructed but no error reported
  |
  = note: delayed at compiler\rustc_typeck\src\check\coercion.rs:153:49


error: internal compiler error: TyKind::Error constructed but no error reported
  |
  = note: delayed at compiler\rustc_mir_build\src\build\mod.rs:696:18


error: internal compiler error: mir_const_qualif: MIR had errors
  --> src\main.rs:10:31
   |
10 |     if let ConstGenericEnum::<N>::Foo(field, ..) = val {
   |                               ^
   |
   = note: delayed at compiler\rustc_mir\src\transform\mod.rs:230:18


error: internal compiler error: PromoteTemps: MIR had errors
  --> src\main.rs:10:31
   |
10 |     if let ConstGenericEnum::<N>::Foo(field, ..) = val {
   |                               ^
   |
   = note: delayed at compiler\rustc_mir\src\transform\promote_consts.rs:55:22


error: internal compiler error: broken MIR in DefId(0:14 ~ consts[4055]::foo::{constant#0}) ("return type"): bad type [type error]
  --> src\main.rs:10:31
   |
10 |     if let ConstGenericEnum::<N>::Foo(field, ..) = val {
   |                               ^
   |
   = note: delayed at compiler\rustc_mir\src\borrow_check\type_check\mod.rs:253:27


error: internal compiler error: TyKind::Error constructed but no error reported
  |
  = note: delayed at compiler\rustc_mir\src\borrow_check\type_check\mod.rs:715:20


error: internal compiler error: broken MIR in DefId(0:14 ~ consts[4055]::foo::{constant#0}) (LocalDecl { mutability: Mut, local_info: None, internal: false, is_block_tail: None, ty: [type error], user_ty: None, source_info: SourceInfo { span: src\main.rs:10:31: 10:32 (#0), scope: scope[0] } }): bad type [type error]
  --> src\main.rs:10:31
   |
10 |     if let ConstGenericEnum::<N>::Foo(field, ..) = val {
   |                               ^
   |
   = note: delayed at compiler\rustc_mir\src\borrow_check\type_check\mod.rs:253:27

Backtrace

thread 'rustc' panicked at 'no errors encountered even though `delay_span_bug` issued', compiler\rustc_errors\src\lib.rs:974:13
stack backtrace:
   0:     0x7ff99bd2bcf5 - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h17841712fc816a42
   1:     0x7ff99bd584fb - core::fmt::write::ha3ea633b18d2da75
   2:     0x7ff99bd1d5dd - <std::io::IoSlice as core::fmt::Debug>::fmt::h9df41d37d9186c48
   3:     0x7ff99bd2fecd - std::panicking::take_hook::h78f8a454f3a4df82
   4:     0x7ff99bd2f9d3 - std::panicking::take_hook::h78f8a454f3a4df82
   5:     0x7ff960e6ff27 - rustc_driver::report_ice::h1d5c5221edf9c73d
   6:     0x7ff99bd309af - std::panicking::rust_panic_with_hook::h9fd6ff93f12148ea
   7:     0x7ff99bd304a1 - rust_begin_unwind
   8:     0x7ff99bd2c69f - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h17841712fc816a42
   9:     0x7ff99bd303f9 - rust_begin_unwind
  10:     0x7ff99bd303ac - std::panicking::begin_panic_fmt::h33e8bdfb545f007a
  11:     0x7ff96569f214 - rustc_errors::HandlerInner::delay_as_bug::h5a7d10ea72b1c82f
  12:     0x7ff96569a8f4 - <rustc_errors::HandlerInner as core::ops::drop::Drop>::drop::hc04473ab921ca342
  13:     0x7ff960e90a47 - rustc_ast::util::parser::prec_let_scrutinee_needs_par::h0da38a96661182e5
  14:     0x7ff960e92eba - rustc_ast::util::parser::prec_let_scrutinee_needs_par::h0da38a96661182e5
  15:     0x7ff960e8dc6c - rustc_ast::util::parser::prec_let_scrutinee_needs_par::h0da38a96661182e5
  16:     0x7ff960e72304 - <rustc_driver::Compilation as core::fmt::Debug>::fmt::hc313d7aa265f4349
  17:     0x7ff960eac7ac - <(rustc_middle::ty::sty::TyVid,&rustc_middle::ty::TyS) as rustc_infer::infer::nll_relate::VidValuePair>::value_ty::h323810e86d8af813
  18:     0x7ff960e810ab - rustc_ast::util::parser::prec_let_scrutinee_needs_par::h0da38a96661182e5
  19:     0x7ff960e08cfd - <tracing_subscriber::util::TryInitError as core::fmt::Display>::fmt::hbce8757813226e4d
  20:     0x7ff99bd3ffd3 - std::sys::windows::thread::Thread::new::h0de7ecb752bc4a62
  21:     0x7ff9f0cb7034 - BaseThreadInitThunk
  22:     0x7ff9f159d0d1 - RtlUserThreadStart
error: internal compiler error: unexpected panic
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 1.51.0-nightly (158f8d034 2020-12-29) running on x86_64-pc-windows-msvc
note: compiler flags: -C embed-bitcode=no -C debuginfo=2 -C incremental --crate-type bin
note: some of the compiler flags provided by cargo are hidden
query stack during panic:
end of query stack

[camelid]

This seems like it's part of min_const_generics – and enabling min_const_generics doesn't fix it – which is worrying.

@rustbot prioritize

[CraftSpider]

Correct, I ran into this with no feature flag

[camelid]

Assigning P-high and removing I-prioritize as discussed in the prioritization working group.