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normalize adt fields during structural match checking #72897

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Jun 11, 2020
Merged

normalize adt fields during structural match checking #72897

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29508ce
normalize adt fields during structural match check
lcnr Jun 1, 2020
4725af3
remove assert
lcnr Jun 2, 2020
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5 changes: 4 additions & 1 deletion src/librustc_trait_selection/traits/structural_match.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -251,7 +251,10 @@ impl<'a, 'tcx> TypeVisitor<'tcx> for Search<'a, 'tcx> {
// fields of ADT.
let tcx = self.tcx();
for field_ty in adt_def.all_fields().map(|field| field.ty(tcx, substs)) {
if field_ty.visit_with(self) {
let ty = self.tcx().normalize_erasing_regions(ty::ParamEnv::empty(), field_ty);
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@eddyb eddyb Jun 4, 2020 •
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ty::Param::empty() is incorrect - frankly I wonder if we should remove it.
You should have a ParamEnv around.

(couple minutes later)

Hang on, this entire file is missing real ParamEnvs?
That's liable to cause ICEs if generic parameters end up in these types.

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Does this block this PR? Afaik it's currently not possible on stable to hit this case.

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I may go ahead and fix this afterwards, but my current priority is mainly to fix #72896
Which probably means that we have to backport this to beta.

Another option would be to revert the structural match check for projections 🤔

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Its probably my fault that we don't have ParamEnvs threaded through here. This whole thing of switching from attributes to traits has been a real rabbit hole.

Still, I think landing this is better than reverting the structural match check for projections.

debug!("structural-match ADT: field_ty={:?}, ty={:?}", field_ty, ty);

if ty.visit_with(self) {
// found an ADT without structural-match; halt visiting!
assert!(self.found.is_some());
return true;
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23 changes: 23 additions & 0 deletions src/test/ui/match/issue-72896.rs
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@@ -0,0 +1,23 @@
// run-pass
trait EnumSetType {
type Repr;
}

enum Enum8 { }
impl EnumSetType for Enum8 {
type Repr = u8;
}

#[derive(PartialEq, Eq)]
struct EnumSet<T: EnumSetType> {
__enumset_underlying: T::Repr,
}

const CONST_SET: EnumSet<Enum8> = EnumSet { __enumset_underlying: 3 };

fn main() {
match CONST_SET {
CONST_SET => { /* ok */ }
_ => panic!("match fell through?"),
}
}