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Auto merge of #116435 - compiler-errors:re-erased, r=lcnr

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Handle `ReErased` in responses in new solver

There are legitimate cases in the compiler where we return `ReErased` for lifetimes that are uncaptured in the hidden type of an opaque. For example, in the test committed below, we ignore ignore the bivariant lifetimes of an opaque when it's inferred as the hidden type of another opaque. This may result in a `type_of(Opaque)` call returning a type that references `ReErased`. Let's handle this gracefully in the new solver.

Also added a `rustc_hidden_type_of_opaques` attr to print hidden types. This seems useful for opaques.

r? lcnr
This commit is contained in:
bors 2023-10-24 08:08:45 +00:00
commit 271dcc1d40
12 changed files with 100 additions and 9 deletions
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12
compiler/rustc_trait_selection/src/solve/canonicalize.rs
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@ -224,12 +224,20 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for Canonicalizer<'_, 'tcx> {
let kind = match *r {
ty::ReLateBound(..) => return r,
ty::ReStatic => match self.canonicalize_mode {
// We may encounter `ReStatic` in item signatures or the hidden type
// of an opaque. `ReErased` should only be encountered in the hidden
// type of an opaque for regions that are ignored for the purposes of
// captures.
//
// FIXME: We should investigate the perf implications of not uniquifying
// `ReErased`. We may be able to short-circuit registering region
// obligations if we encounter a `ReErased` on one side, for example.
ty::ReStatic | ty::ReErased => match self.canonicalize_mode {
CanonicalizeMode::Input => CanonicalVarKind::Region(ty::UniverseIndex::ROOT),
CanonicalizeMode::Response { .. } => return r,
},
ty::ReErased | ty::ReFree(_) | ty::ReEarlyBound(_) => match self.canonicalize_mode {
ty::ReFree(_) | ty::ReEarlyBound(_) => match self.canonicalize_mode {
CanonicalizeMode::Input => CanonicalVarKind::Region(ty::UniverseIndex::ROOT),
CanonicalizeMode::Response { .. } => bug!("unexpected region in response: {r:?}"),
},