ICE: Unexpected type for constructor Variant(1)

[Luv-Ray]

I try to reduce the code of #125155 and find the ice changed.
Maybe duplicated with #120601 and #124004, but I think the code here is cleaner.

Code

enum NestedEnum {
    First,
    Second,
}

enum Enum {
    Variant(*const &'a ()),
}

fn foo(x: Enum) {
    match x {
        Enum::Variant(NestedEnum::Second) => {}
    }
}

fn main() {}

Meta

rustc --version --verbose:

rustc 1.80.0-nightly (6f3df08aa 2024-05-30)
binary: rustc
commit-hash: 6f3df08aadf71e8d4bf7e49f5dc10dfa6f254cb4
commit-date: 2024-05-30
host: x86_64-unknown-linux-gnu
release: 1.80.0-nightly
LLVM version: 18.1.6

Error output

error[E0261]: use of undeclared lifetime name `'a`
 --> src/main.rs:7:21
  |
6 | enum Enum {
  |          - help: consider introducing lifetime `'a` here: `<'a>`
7 |     Variant(*const &'a ()),
  |                     ^^ undeclared lifetime

error: internal compiler error: compiler/rustc_pattern_analysis/src/rustc.rs:236:22: Unexpected type for constructor `Variant(1)`: *const &'{erased} ()

thread 'rustc' panicked at compiler/rustc_pattern_analysis/src/rustc.rs:236:22:
Box<dyn Any>
stack backtrace:
   0:     0x7b7b729f9dfb - std::backtrace_rs::backtrace::libunwind::trace::h7d54eacc88008817
                               at /rustc/6f3df08aadf71e8d4bf7e49f5dc10dfa6f254cb4/library/std/src/../../backtrace/src/backtrace/libunwind.rs:116:5
   1:     0x7b7b729f9dfb - std::backtrace_rs::backtrace::trace_unsynchronized::h1b384a49badbbbf0
                               at /rustc/6f3df08aadf71e8d4bf7e49f5dc10dfa6f254cb4/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2:     0x7b7b729f9dfb - std::backtrace::Backtrace::create::ha4add90f9a9ffcbb
                               at /rustc/6f3df08aadf71e8d4bf7e49f5dc10dfa6f254cb4/library/std/src/backtrace.rs:331:13
   3:     0x7b7b729f9d45 - std::backtrace::Backtrace::force_capture::he209e47860813be1
                               at /rustc/6f3df08aadf71e8d4bf7e49f5dc10dfa6f254cb4/library/std/src/backtrace.rs:312:9
   4:     0x7b7b6f13432a - std[362b16250628d2ae]::panicking::update_hook::<alloc[36c56ba0e371072d]::boxed::Box<rustc_driver_impl[33236637d18b51d0]::install_ice_hook::{closure#0}>>::{closure#0}
   5:     0x7b7b72a14c2b - <alloc::boxed::Box<F,A> as core::ops::function::Fn<Args>>::call::h1df67ed3fceec998
                               at /rustc/6f3df08aadf71e8d4bf7e49f5dc10dfa6f254cb4/library/alloc/src/boxed.rs:2077:9
   6:     0x7b7b72a14c2b - std::panicking::rust_panic_with_hook::h7947d7d7856ccdd3
                               at /rustc/6f3df08aadf71e8d4bf7e49f5dc10dfa6f254cb4/library/std/src/panicking.rs:799:13
   7:     0x7b7b6f164644 - std[362b16250628d2ae]::panicking::begin_panic::<rustc_errors[59a72888fd61d3ce]::ExplicitBug>::{closure#0}
   8:     0x7b7b6f160f76 - std[362b16250628d2ae]::sys_common::backtrace::__rust_end_short_backtrace::<std[362b16250628d2ae]::panicking::begin_panic<rustc_errors[59a72888fd61d3ce]::ExplicitBug>::{closure#0}, !>
   9:     0x7b7b6f15c2c6 - std[362b16250628d2ae]::panicking::begin_panic::<rustc_errors[59a72888fd61d3ce]::ExplicitBug>
  10:     0x7b7b6f16dae1 - <rustc_errors[59a72888fd61d3ce]::diagnostic::BugAbort as rustc_errors[59a72888fd61d3ce]::diagnostic::EmissionGuarantee>::emit_producing_guarantee
  11:     0x7b7b6f64d31c - rustc_middle[d10142e9169e5087]::util::bug::opt_span_bug_fmt::<rustc_span[6ca5b1b463c06ed1]::span_encoding::Span>::{closure#0}
  12:     0x7b7b6f63055a - rustc_middle[d10142e9169e5087]::ty::context::tls::with_opt::<rustc_middle[d10142e9169e5087]::util::bug::opt_span_bug_fmt<rustc_span[6ca5b1b463c06ed1]::span_encoding::Span>::{closure#0}, !>::{closure#0}
  13:     0x7b7b6f6303fb - rustc_middle[d10142e9169e5087]::ty::context::tls::with_context_opt::<rustc_middle[d10142e9169e5087]::ty::context::tls::with_opt<rustc_middle[d10142e9169e5087]::util::bug::opt_span_bug_fmt<rustc_span[6ca5b1b463c06ed1]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  14:     0x7b7b6d9eb1a0 - rustc_middle[d10142e9169e5087]::util::bug::bug_fmt
  15:     0x7b7b70e1d8cb - rustc_pattern_analysis[8a3e0b8a86761bb1]::usefulness::compute_exhaustiveness_and_usefulness::<rustc_pattern_analysis[8a3e0b8a86761bb1]::rustc::RustcPatCtxt>::{closure#0}
  16:     0x7b7b70e178f3 - rustc_pattern_analysis[8a3e0b8a86761bb1]::usefulness::compute_exhaustiveness_and_usefulness::<rustc_pattern_analysis[8a3e0b8a86761bb1]::rustc::RustcPatCtxt>::{closure#0}
  17:     0x7b7b70e0e704 - rustc_pattern_analysis[8a3e0b8a86761bb1]::analyze_match
  18:     0x7b7b6daa9d42 - <rustc_mir_build[bacafdeaff7b19ff]::thir::pattern::check_match::MatchVisitor as rustc_middle[d10142e9169e5087]::thir::visit::Visitor>::visit_expr
  19:     0x7b7b6daa92bd - <rustc_mir_build[bacafdeaff7b19ff]::thir::pattern::check_match::MatchVisitor as rustc_middle[d10142e9169e5087]::thir::visit::Visitor>::visit_expr
  20:     0x7b7b6daaa134 - <rustc_mir_build[bacafdeaff7b19ff]::thir::pattern::check_match::MatchVisitor as rustc_middle[d10142e9169e5087]::thir::visit::Visitor>::visit_expr
  21:     0x7b7b6daa92bd - <rustc_mir_build[bacafdeaff7b19ff]::thir::pattern::check_match::MatchVisitor as rustc_middle[d10142e9169e5087]::thir::visit::Visitor>::visit_expr
  22:     0x7b7b70873686 - rustc_mir_build[bacafdeaff7b19ff]::thir::pattern::check_match::check_match
  23:     0x7b7b7087326d - rustc_query_impl[a4ad450ce75c81f3]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[a4ad450ce75c81f3]::query_impl::check_match::dynamic_query::{closure#2}::{closure#0}, rustc_middle[d10142e9169e5087]::query::erase::Erased<[u8; 1usize]>>
  24:     0x7b7b70ad1b0e - rustc_query_system[466e502815dde757]::query::plumbing::try_execute_query::<rustc_query_impl[a4ad450ce75c81f3]::DynamicConfig<rustc_query_system[466e502815dde757]::query::caches::VecCache<rustc_span[6ca5b1b463c06ed1]::def_id::LocalDefId, rustc_middle[d10142e9169e5087]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[a4ad450ce75c81f3]::plumbing::QueryCtxt, true>
  25:     0x7b7b706e5aad - rustc_query_impl[a4ad450ce75c81f3]::query_impl::check_match::get_query_incr::__rust_end_short_backtrace
  26:     0x7b7b7087afc9 - rustc_mir_build[bacafdeaff7b19ff]::build::mir_build
  27:     0x7b7b7087a68e - rustc_query_impl[a4ad450ce75c81f3]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[a4ad450ce75c81f3]::query_impl::mir_built::dynamic_query::{closure#2}::{closure#0}, rustc_middle[d10142e9169e5087]::query::erase::Erased<[u8; 8usize]>>
  28:     0x7b7b70c69776 - rustc_query_system[466e502815dde757]::query::plumbing::try_execute_query::<rustc_query_impl[a4ad450ce75c81f3]::DynamicConfig<rustc_query_system[466e502815dde757]::query::caches::VecCache<rustc_span[6ca5b1b463c06ed1]::def_id::LocalDefId, rustc_middle[d10142e9169e5087]::query::erase::Erased<[u8; 8usize]>>, false, false, false>, rustc_query_impl[a4ad450ce75c81f3]::plumbing::QueryCtxt, true>
  29:     0x7b7b70ad985c - rustc_query_impl[a4ad450ce75c81f3]::query_impl::mir_built::get_query_incr::__rust_end_short_backtrace
  30:     0x7b7b70c76aa6 - rustc_mir_build[bacafdeaff7b19ff]::check_unsafety::check_unsafety
  31:     0x7b7b70c76847 - rustc_query_impl[a4ad450ce75c81f3]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[a4ad450ce75c81f3]::query_impl::check_unsafety::dynamic_query::{closure#2}::{closure#0}, rustc_middle[d10142e9169e5087]::query::erase::Erased<[u8; 0usize]>>
  32:     0x7b7b70ad7c61 - rustc_query_system[466e502815dde757]::query::plumbing::try_execute_query::<rustc_query_impl[a4ad450ce75c81f3]::DynamicConfig<rustc_query_system[466e502815dde757]::query::caches::VecCache<rustc_span[6ca5b1b463c06ed1]::def_id::LocalDefId, rustc_middle[d10142e9169e5087]::query::erase::Erased<[u8; 0usize]>>, false, false, false>, rustc_query_impl[a4ad450ce75c81f3]::plumbing::QueryCtxt, true>
  33:     0x7b7b70ad777f - rustc_query_impl[a4ad450ce75c81f3]::query_impl::check_unsafety::get_query_incr::__rust_end_short_backtrace
  34:     0x7b7b70c7d05b - rustc_interface[749128fb2397a9e]::passes::analysis
  35:     0x7b7b70c7c15b - rustc_query_impl[a4ad450ce75c81f3]::plumbing::__rust_begin_short_backtrace::<rustc_query_impl[a4ad450ce75c81f3]::query_impl::analysis::dynamic_query::{closure#2}::{closure#0}, rustc_middle[d10142e9169e5087]::query::erase::Erased<[u8; 1usize]>>
  36:     0x7b7b7156640a - rustc_query_system[466e502815dde757]::query::plumbing::try_execute_query::<rustc_query_impl[a4ad450ce75c81f3]::DynamicConfig<rustc_query_system[466e502815dde757]::query::caches::SingleCache<rustc_middle[d10142e9169e5087]::query::erase::Erased<[u8; 1usize]>>, false, false, false>, rustc_query_impl[a4ad450ce75c81f3]::plumbing::QueryCtxt, true>
  37:     0x7b7b7156603a - rustc_query_impl[a4ad450ce75c81f3]::query_impl::analysis::get_query_incr::__rust_end_short_backtrace
  38:     0x7b7b711ee71c - rustc_interface[749128fb2397a9e]::interface::run_compiler::<core[5f8c442e32640be5]::result::Result<(), rustc_span[6ca5b1b463c06ed1]::ErrorGuaranteed>, rustc_driver_impl[33236637d18b51d0]::run_compiler::{closure#0}>::{closure#1}
  39:     0x7b7b711d97e7 - std[362b16250628d2ae]::sys_common::backtrace::__rust_begin_short_backtrace::<rustc_interface[749128fb2397a9e]::util::run_in_thread_with_globals<rustc_interface[749128fb2397a9e]::util::run_in_thread_pool_with_globals<rustc_interface[749128fb2397a9e]::interface::run_compiler<core[5f8c442e32640be5]::result::Result<(), rustc_span[6ca5b1b463c06ed1]::ErrorGuaranteed>, rustc_driver_impl[33236637d18b51d0]::run_compiler::{closure#0}>::{closure#1}, core[5f8c442e32640be5]::result::Result<(), rustc_span[6ca5b1b463c06ed1]::ErrorGuaranteed>>::{closure#0}, core[5f8c442e32640be5]::result::Result<(), rustc_span[6ca5b1b463c06ed1]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[5f8c442e32640be5]::result::Result<(), rustc_span[6ca5b1b463c06ed1]::ErrorGuaranteed>>
  40:     0x7b7b711d95aa - <<std[362b16250628d2ae]::thread::Builder>::spawn_unchecked_<rustc_interface[749128fb2397a9e]::util::run_in_thread_with_globals<rustc_interface[749128fb2397a9e]::util::run_in_thread_pool_with_globals<rustc_interface[749128fb2397a9e]::interface::run_compiler<core[5f8c442e32640be5]::result::Result<(), rustc_span[6ca5b1b463c06ed1]::ErrorGuaranteed>, rustc_driver_impl[33236637d18b51d0]::run_compiler::{closure#0}>::{closure#1}, core[5f8c442e32640be5]::result::Result<(), rustc_span[6ca5b1b463c06ed1]::ErrorGuaranteed>>::{closure#0}, core[5f8c442e32640be5]::result::Result<(), rustc_span[6ca5b1b463c06ed1]::ErrorGuaranteed>>::{closure#0}::{closure#0}, core[5f8c442e32640be5]::result::Result<(), rustc_span[6ca5b1b463c06ed1]::ErrorGuaranteed>>::{closure#2} as core[5f8c442e32640be5]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  41:     0x7b7b72a1ebfb - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hc666fad739fe414e
                               at /rustc/6f3df08aadf71e8d4bf7e49f5dc10dfa6f254cb4/library/alloc/src/boxed.rs:2063:9
  42:     0x7b7b72a1ebfb - <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once::hcd8201f663299c4b
                               at /rustc/6f3df08aadf71e8d4bf7e49f5dc10dfa6f254cb4/library/alloc/src/boxed.rs:2063:9
  43:     0x7b7b72a1ebfb - std::sys::pal::unix::thread::Thread::new::thread_start::h4f248c4f539e2e55
                               at /rustc/6f3df08aadf71e8d4bf7e49f5dc10dfa6f254cb4/library/std/src/sys/pal/unix/thread.rs:108:17
  44:     0x7b7b727caded - <unknown>
  45:     0x7b7b7284e0dc - <unknown>
  46:                0x0 - <unknown>


rustc version: 1.80.0-nightly (6f3df08aa 2024-05-30)
platform: x86_64-unknown-linux-gnu

query stack during panic:
#0 [check_match] match-checking `foo`
#1 [mir_built] building MIR for `foo`
#2 [check_unsafety] unsafety-checking `foo`
#3 [analysis] running analysis passes on this crate
end of query stack

[Luv-Ray]

My thought after some debug:
There are some ways to trigger panic in compiler/rustc_pattern_analysis, because we trust that the type analysed here are all correct but they may not.

Consider two programs below:

// program A
enum NestedEnum {
    First,
    Second,
}

enum Enum {
    Variant(*const ()),
    // Variant(*const &'a ()),
}

fn foo(x: Enum) {
    match x {
        Enum::Variant(NestedEnum::Second) => {}
    }
}

// program B
enum NestedEnum {
    First,
    Second,
}

enum Enum {
    // Variant(*const ()),
    Variant(*const &'a ()),
}

fn foo(x: Enum) {
    match x {
        Enum::Variant(NestedEnum::Second) => {}
    }
}

program B will panic at compile while program A not. The difference occurs here:

rust/compiler/rustc_mir_build/src/thir/pattern/check_match.rs

Lines 29 to 32 in 6a207f4

	pub(crate) fn check_match(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Result<(), ErrorGuaranteed> {
	let typeck_results = tcx.typeck(def_id);
	let (thir, expr) = tcx.thir_body(def_id)?;
	let thir = thir.borrow();

program A will early return at tcx.thir_body(def_id)?, but program B will not and cause the panic.
I have checked the typeck_results of two programs, and there is a key different between them: in program A typeck_results.tainted_by_errors is Some(ErrorGuaranteed(())), and in program B that is None.

A:

TypeckResults { hir_owner: DefId(0:12 ~ tmp[d0fa]::foo), type_dependent_defs: UnordMap { inner: {} }, field_indices: UnordMap { inner: {} }, nested_fields: UnordMap { inner: {} }, node_types: UnordMap { inner: {16: (), 13: (), 10: NestedEnum, 4: Enum, 1: Enum, 14: (), 11: Enum, 2: Enum, 15: (), 3: ()} }, node_args: UnordMap { inner: {} }, user_provided_types: UnordMap { inner: {} }, user_provided_sigs: UnordMap { inner: {} }, adjustments: UnordMap { inner: {} }, pat_binding_modes: UnordMap { inner: {2: BindingMode(No, Not)} }, rust_2024_migration_desugared_pats: UnordSet { inner: {} }, pat_adjustments: UnordMap { inner: {} }, skipped_ref_pats: UnordSet { inner: {} }, closure_kind_origins: UnordMap { inner: {} }, liberated_fn_sigs: UnordMap { inner: {0: fn(Enum)} }, fru_field_types: UnordMap { inner: {} }, coercion_casts: UnordSet { inner: {} }, used_trait_imports: UnordSet { inner: {} }, tainted_by_errors: Some(ErrorGuaranteed(())), concrete_opaque_types: {}, closure_min_captures: UnordMap { inner: {} }, closure_fake_reads: UnordMap { inner: {} }, rvalue_scopes: RvalueScopes { map: UnordMap { inner: {} } }, coroutine_stalled_predicates: {}, treat_byte_string_as_slice: UnordSet { inner: {} }, closure_size_eval: UnordMap { inner: {} }, offset_of_data: UnordMap { inner: {} }, inline_consts: {} }

B:

TypeckResults { hir_owner: DefId(0:12 ~ tmp2[62c9]::foo), type_dependent_defs: UnordMap { inner: {} }, field_indices: UnordMap { inner: {} }, nested_fields: UnordMap { inner: {} }, node_types: UnordMap { inner: {16: (), 13: (), 10: NestedEnum, 4: Enum, 1: Enum, 14: (), 11: Enum, 2: Enum, 15: (), 3: ()} }, node_args: UnordMap { inner: {} }, user_provided_types: UnordMap { inner: {} }, user_provided_sigs: UnordMap { inner: {} }, adjustments: UnordMap { inner: {} }, pat_binding_modes: UnordMap { inner: {2: BindingMode(No, Not)} }, rust_2024_migration_desugared_pats: UnordSet { inner: {} }, pat_adjustments: UnordMap { inner: {} }, skipped_ref_pats: UnordSet { inner: {} }, closure_kind_origins: UnordMap { inner: {} }, liberated_fn_sigs: UnordMap { inner: {0: fn(Enum)} }, fru_field_types: UnordMap { inner: {} }, coercion_casts: UnordSet { inner: {} }, used_trait_imports: UnordSet { inner: {} }, tainted_by_errors: None, concrete_opaque_types: {}, closure_min_captures: UnordMap { inner: {} }, closure_fake_reads: UnordMap { inner: {} }, rvalue_scopes: RvalueScopes { map: UnordMap { inner: {} } }, coroutine_stalled_predicates: {}, treat_byte_string_as_slice: UnordSet { inner: {} }, closure_size_eval: UnordMap { inner: {} }, offset_of_data: UnordMap { inner: {} }, inline_consts: {} }

In TyCtxt::thir_body's comment, it says: If typeck for that body failed, returns an empty Thir., but seems that it return ErrorGuaranteed rather than empty Thir if typeck failed. Is the description wrong here?

[Luv-Ray]

Because this hack, I think.

rust/compiler/rustc_hir_typeck/src/writeback.rs

Lines 125 to 130 in 76c7382

	// HACK: We specifically don't want the (opaque) error from tainting our
	// inference context. That'll prevent us from doing opaque type inference
	// later on in borrowck, which affects diagnostic spans pretty negatively.
	if let Some(e) = fcx.tainted_by_errors() {
	wbcx.typeck_results.tainted_by_errors = Some(e);
	}

[Luv-Ray]

program A set tainted_by_errors to Some(ErrorGuaranteed(())) here, but program B not.

rust/compiler/rustc_hir_typeck/src/pat.rs

Line 1165 in 921645c

e.emit();