Description
openedon Aug 25, 2018
Update from @pnkfelix:
Our behavior on this test case (playpen) has changed, but it is still not correct.
#[derive(PartialEq, Eq)]
struct S;
fn main() {
const C: &S = &S;
match C {
C => {}
}
}emits error:
error[E0004]: non-exhaustive patterns: `&S` not covered
--> src/main.rs:6:11
|
6 | match C {
| ^ pattern `&S` not covered
|
= help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
If you work-around the exhaustiveness checker bug by e.g. adding an unreachable arm, then the compiler accepts the code (and as far as I can tell, assigns it the correct runtime semantics).
Original bug report follows:
struct S;
fn main() {
const C: &S = &S;
match C {
C => {}
}
}gives:
error: internal compiler error: librustc_mir/hair/pattern/_match.rs:432: bad constructor ConstantValue(Const { ty: &S, val: Scalar(Ptr(Pointer { alloc_id: AllocId(1), offset: Size { raw: 0 } })) }) for adt S
The relevant stack is:
14: rustc_mir::hair::pattern::_match::Constructor::variant_index_for_adt
15: rustc_mir::hair::pattern::_match::constructor_sub_pattern_tys
16: rustc_mir::hair::pattern::_match::is_useful_specialized
17: <core::iter::Map<I, F> as core::iter::iterator::Iterator>::try_fold
18: rustc_mir::hair::pattern::_match::is_useful
19: rustc_mir::hair::pattern::_match::is_useful_specialized
20: <core::iter::Map<I, F> as core::iter::iterator::Iterator>::try_fold
21: rustc_mir::hair::pattern::_match::is_useful
22: rustc_mir::hair::pattern::check_match::check_arms
23: rustc_mir::hair::pattern::_match::MatchCheckCtxt::create_and_enter
24: <rustc_mir::hair::pattern::check_match::MatchVisitor<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_expr
25: <rustc_mir::hair::pattern::check_match::MatchVisitor<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_expr
26: <rustc_mir::hair::pattern::check_match::MatchVisitor<'a, 'tcx> as rustc::hir::intravisit::Visitor<'tcx>>::visit_body
27: rustc::session::Session::track_errors
28: rustc_mir::hair::pattern::check_match::check_match
29: rustc::ty::query::<impl rustc::ty::query::config::QueryAccessors<'tcx> for rustc::ty::query::queries::check_match<'tcx>>::compute
30: rustc::dep_graph::graph::DepGraph::with_task_impl
31: <rustc::ty::query::plumbing::JobOwner<'a, 'tcx, Q>>::start
32: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::force_query_with_job
33: rustc::ty::query::plumbing::<impl rustc::ty::context::TyCtxt<'a, 'gcx, 'tcx>>::get_query
34: rustc::hir::intravisit::Visitor::visit_nested_body
35: rustc::hir::Crate::visit_all_item_likes
36: rustc_mir::hair::pattern::check_match::check_crate
It looks like this will take some effort to fix, I patched constructor_sub_pattern_tys to return vec![], but then rustc erroneously reports
error[E0004]: non-exhaustive patterns: '&S' not covered
and with an enum:
enum E {A}
fn main() {
const C: &E = &E::A;
match C {
C => {}
_ => {}
}
}it hits:
error: internal compiler error: librustc\traits\codegen\mod.rs:169: Encountered errors '[FulfillmentError(Obligation(predicate=Binder(TraitPredicate(<E as std::cmp::PartialEq>)),depth=1),Unimplemented)]' resolving bounds after type-checking
