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Auto merge of #107969 - b-naber:proj-relate-variance, r=lcnr

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Use covariance on type relations of field projection types if possible

It's fine to use covariance here unless we're in a mutating context.

Fixes https://github.com/rust-lang/rust/issues/96514

Supersedes https://github.com/rust-lang/rust/pull/105958

r? `@lcnr`
This commit is contained in:
bors 2023-02-20 09:25:51 +00:00
commit e7eaed21d5
8 changed files with 159 additions and 4 deletions
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29
compiler/rustc_borrowck/src/type_check/mod.rs
View file

@ -534,7 +534,7 @@ impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
return PlaceTy::from_ty(self.tcx().ty_error());
}
}
place_ty = self.sanitize_projection(place_ty, elem, place, location);
place_ty = self.sanitize_projection(place_ty, elem, place, location, context);
}
if let PlaceContext::NonMutatingUse(NonMutatingUseContext::Copy) = context {
@ -630,12 +630,14 @@ impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
}
}
#[instrument(skip(self), level = "debug")]
fn sanitize_projection(
&mut self,
base: PlaceTy<'tcx>,
pi: PlaceElem<'tcx>,
place: &Place<'tcx>,
location: Location,
context: PlaceContext,
) -> PlaceTy<'tcx> {
debug!("sanitize_projection: {:?} {:?} {:?}", base, pi, place);
let tcx = self.tcx();
@ -713,8 +715,11 @@ impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
match self.field_ty(place, base, field, location) {
Ok(ty) => {
let ty = self.cx.normalize(ty, location);
if let Err(terr) = self.cx.eq_types(
debug!(?fty, ?ty);
if let Err(terr) = self.cx.relate_types(
ty,
self.get_ambient_variance(context),
fty,
location.to_locations(),
ConstraintCategory::Boring,
@ -743,9 +748,10 @@ impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
let ty = self.sanitize_type(place, ty);
let ty = self.cx.normalize(ty, location);
self.cx
.eq_types(
base.ty,
.relate_types(
ty,
self.get_ambient_variance(context),
base.ty,
location.to_locations(),
ConstraintCategory::TypeAnnotation,
)
@ -760,6 +766,21 @@ impl<'a, 'b, 'tcx> TypeVerifier<'a, 'b, 'tcx> {
self.tcx().ty_error()
}
fn get_ambient_variance(&self, context: PlaceContext) -> ty::Variance {
use rustc_middle::mir::visit::NonMutatingUseContext::*;
use rustc_middle::mir::visit::NonUseContext::*;
match context {
PlaceContext::MutatingUse(_) => ty::Invariant,
PlaceContext::NonUse(StorageDead | StorageLive | VarDebugInfo) => ty::Invariant,
PlaceContext::NonMutatingUse(
Inspect | Copy | Move | SharedBorrow | ShallowBorrow | UniqueBorrow | AddressOf
| Projection,
) => ty::Covariant,
PlaceContext::NonUse(AscribeUserTy) => ty::Covariant,
}
}
fn field_ty(
&mut self,
parent: &dyn fmt::Debug,