diff --git a/compiler/rustc_borrowck/src/nll.rs b/compiler/rustc_borrowck/src/nll.rs
index d2e8227479271..0961203d76d7d 100644
--- a/compiler/rustc_borrowck/src/nll.rs
+++ b/compiler/rustc_borrowck/src/nll.rs
@@ -1,7 +1,7 @@
 //! The entry point of the NLL borrow checker.
 
 use rustc_data_structures::vec_map::VecMap;
-use rustc_hir::def_id::DefId;
+use rustc_hir::def_id::LocalDefId;
 use rustc_index::vec::IndexVec;
 use rustc_infer::infer::InferCtxt;
 use rustc_middle::mir::{create_dump_file, dump_enabled, dump_mir, PassWhere};
@@ -44,7 +44,7 @@ pub type PoloniusOutput = Output<RustcFacts>;
 /// closure requirements to propagate, and any generated errors.
 pub(crate) struct NllOutput<'tcx> {
     pub regioncx: RegionInferenceContext<'tcx>,
-    pub opaque_type_values: VecMap<DefId, OpaqueHiddenType<'tcx>>,
+    pub opaque_type_values: VecMap<LocalDefId, OpaqueHiddenType<'tcx>>,
     pub polonius_input: Option<Box<AllFacts>>,
     pub polonius_output: Option<Rc<PoloniusOutput>>,
     pub opt_closure_req: Option<ClosureRegionRequirements<'tcx>>,
@@ -373,7 +373,7 @@ pub(super) fn dump_annotation<'a, 'tcx>(
     body: &Body<'tcx>,
     regioncx: &RegionInferenceContext<'tcx>,
     closure_region_requirements: &Option<ClosureRegionRequirements<'_>>,
-    opaque_type_values: &VecMap<DefId, OpaqueHiddenType<'tcx>>,
+    opaque_type_values: &VecMap<LocalDefId, OpaqueHiddenType<'tcx>>,
     errors: &mut crate::error::BorrowckErrors<'tcx>,
 ) {
     let tcx = infcx.tcx;
diff --git a/compiler/rustc_borrowck/src/region_infer/opaque_types.rs b/compiler/rustc_borrowck/src/region_infer/opaque_types.rs
index 7c1fa28b8dfcc..de9da84572983 100644
--- a/compiler/rustc_borrowck/src/region_infer/opaque_types.rs
+++ b/compiler/rustc_borrowck/src/region_infer/opaque_types.rs
@@ -1,6 +1,6 @@
 use rustc_data_structures::fx::FxHashMap;
 use rustc_data_structures::vec_map::VecMap;
-use rustc_hir::def_id::DefId;
+use rustc_hir::def_id::LocalDefId;
 use rustc_hir::OpaqueTyOrigin;
 use rustc_infer::infer::error_reporting::unexpected_hidden_region_diagnostic;
 use rustc_infer::infer::InferCtxt;
@@ -63,8 +63,8 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         &self,
         infcx: &InferCtxt<'_, 'tcx>,
         opaque_ty_decls: VecMap<OpaqueTypeKey<'tcx>, (OpaqueHiddenType<'tcx>, OpaqueTyOrigin)>,
-    ) -> VecMap<DefId, OpaqueHiddenType<'tcx>> {
-        let mut result: VecMap<DefId, OpaqueHiddenType<'tcx>> = VecMap::new();
+    ) -> VecMap<LocalDefId, OpaqueHiddenType<'tcx>> {
+        let mut result: VecMap<LocalDefId, OpaqueHiddenType<'tcx>> = VecMap::new();
         for (opaque_type_key, (concrete_type, origin)) in opaque_ty_decls {
             let substs = opaque_type_key.substs;
             debug!(?concrete_type, ?substs);
@@ -235,7 +235,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
         // lifetimes with 'static and remapping only those used in the
         // `impl Trait` return type, resulting in the parameters
         // shifting.
-        let id_substs = InternalSubsts::identity_for_item(self.tcx, def_id);
+        let id_substs = InternalSubsts::identity_for_item(self.tcx, def_id.to_def_id());
         debug!(?id_substs);
         let map: FxHashMap<GenericArg<'tcx>, GenericArg<'tcx>> =
             substs.iter().enumerate().map(|(index, subst)| (subst, id_substs[index])).collect();
@@ -268,7 +268,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             // This logic duplicates most of `check_opaque_meets_bounds`.
             // FIXME(oli-obk): Also do region checks here and then consider removing `check_opaque_meets_bounds` entirely.
             let param_env = self.tcx.param_env(def_id);
-            let body_id = self.tcx.local_def_id_to_hir_id(def_id.as_local().unwrap());
+            let body_id = self.tcx.local_def_id_to_hir_id(def_id);
             self.tcx.infer_ctxt().enter(move |infcx| {
                 // Require the hidden type to be well-formed with only the generics of the opaque type.
                 // Defining use functions may have more bounds than the opaque type, which is ok, as long as the
@@ -296,7 +296,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                         infcx
                             .report_mismatched_types(
                                 &ObligationCause::misc(instantiated_ty.span, body_id),
-                                self.tcx.mk_opaque(def_id, id_substs),
+                                self.tcx.mk_opaque(def_id.to_def_id(), id_substs),
                                 definition_ty,
                                 err,
                             )
@@ -423,7 +423,7 @@ fn check_opaque_type_parameter_valid(
 struct ReverseMapper<'tcx> {
     tcx: TyCtxt<'tcx>,
 
-    opaque_type_def_id: DefId,
+    opaque_type_def_id: LocalDefId,
     map: FxHashMap<GenericArg<'tcx>, GenericArg<'tcx>>,
     map_missing_regions_to_empty: bool,
 
@@ -437,7 +437,7 @@ struct ReverseMapper<'tcx> {
 impl<'tcx> ReverseMapper<'tcx> {
     fn new(
         tcx: TyCtxt<'tcx>,
-        opaque_type_def_id: DefId,
+        opaque_type_def_id: LocalDefId,
         map: FxHashMap<GenericArg<'tcx>, GenericArg<'tcx>>,
         hidden_ty: Ty<'tcx>,
         span: Span,
diff --git a/compiler/rustc_const_eval/src/interpret/visitor.rs b/compiler/rustc_const_eval/src/interpret/visitor.rs
index f6a0c19d25953..3f6e8a8f755a1 100644
--- a/compiler/rustc_const_eval/src/interpret/visitor.rs
+++ b/compiler/rustc_const_eval/src/interpret/visitor.rs
@@ -473,6 +473,9 @@ macro_rules! make_value_visitor {
                         // The second `Box` field is the allocator, which we recursively check for validity
                         // like in regular structs.
                         self.visit_field(v, 1, &alloc)?;
+
+                        // We visited all parts of this one.
+                        return Ok(());
                     }
                     _ => {},
                 };
diff --git a/compiler/rustc_infer/src/infer/canonical/query_response.rs b/compiler/rustc_infer/src/infer/canonical/query_response.rs
index 1e8b212276f2f..8dc20544f1b1a 100644
--- a/compiler/rustc_infer/src/infer/canonical/query_response.rs
+++ b/compiler/rustc_infer/src/infer/canonical/query_response.rs
@@ -153,7 +153,7 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
             .opaque_type_storage
             .take_opaque_types()
             .into_iter()
-            .map(|(k, v)| (self.tcx.mk_opaque(k.def_id, k.substs), v.hidden_type.ty))
+            .map(|(k, v)| (self.tcx.mk_opaque(k.def_id.to_def_id(), k.substs), v.hidden_type.ty))
             .collect()
     }
 
diff --git a/compiler/rustc_infer/src/infer/mod.rs b/compiler/rustc_infer/src/infer/mod.rs
index c5a342c1ba2ca..b3dc2e586d251 100644
--- a/compiler/rustc_infer/src/infer/mod.rs
+++ b/compiler/rustc_infer/src/infer/mod.rs
@@ -938,7 +938,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     #[instrument(skip(self), level = "debug")]
     pub fn member_constraint(
         &self,
-        opaque_type_def_id: DefId,
+        opaque_type_def_id: LocalDefId,
         definition_span: Span,
         hidden_ty: Ty<'tcx>,
         region: ty::Region<'tcx>,
diff --git a/compiler/rustc_infer/src/infer/opaque_types.rs b/compiler/rustc_infer/src/infer/opaque_types.rs
index f11701bba6f43..4ee9c4eeda40a 100644
--- a/compiler/rustc_infer/src/infer/opaque_types.rs
+++ b/compiler/rustc_infer/src/infer/opaque_types.rs
@@ -51,7 +51,11 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             return InferOk { value: ty, obligations: vec![] };
         }
         let mut obligations = vec![];
-        let replace_opaque_type = |def_id| self.opaque_type_origin(def_id, span).is_some();
+        let replace_opaque_type = |def_id: DefId| {
+            def_id
+                .as_local()
+                .map_or(false, |def_id| self.opaque_type_origin(def_id, span).is_some())
+        };
         let value = ty.fold_with(&mut ty::fold::BottomUpFolder {
             tcx: self.tcx,
             lt_op: |lt| lt,
@@ -96,6 +100,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         let (a, b) = if a_is_expected { (a, b) } else { (b, a) };
         let process = |a: Ty<'tcx>, b: Ty<'tcx>| match *a.kind() {
             ty::Opaque(def_id, substs) if def_id.is_local() => {
+                let def_id = def_id.expect_local();
                 let origin = if self.defining_use_anchor.is_some() {
                     // Check that this is `impl Trait` type is
                     // declared by `parent_def_id` -- i.e., one whose
@@ -141,7 +146,8 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                     // no one encounters it in practice.
                     // It does occur however in `fn fut() -> impl Future<Output = i32> { async { 42 } }`,
                     // where it is of no concern, so we only check for TAITs.
-                    if let Some(OpaqueTyOrigin::TyAlias) = self.opaque_type_origin(did2, cause.span)
+                    if let Some(OpaqueTyOrigin::TyAlias) =
+                        did2.as_local().and_then(|did2| self.opaque_type_origin(did2, cause.span))
                     {
                         self.tcx
                                 .sess
@@ -399,8 +405,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     }
 
     #[instrument(skip(self), level = "trace")]
-    pub fn opaque_type_origin(&self, opaque_def_id: DefId, span: Span) -> Option<OpaqueTyOrigin> {
-        let def_id = opaque_def_id.as_local()?;
+    pub fn opaque_type_origin(&self, def_id: LocalDefId, span: Span) -> Option<OpaqueTyOrigin> {
         let opaque_hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id);
         let parent_def_id = self.defining_use_anchor?;
         let item_kind = &self.tcx.hir().expect_item(def_id).kind;
@@ -409,7 +414,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             span_bug!(
                 span,
                 "weird opaque type: {:#?}, {:#?}",
-                opaque_def_id,
+                def_id,
                 item_kind
             )
         };
@@ -428,12 +433,11 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     }
 
     #[instrument(skip(self), level = "trace")]
-    fn opaque_ty_origin_unchecked(&self, opaque_def_id: DefId, span: Span) -> OpaqueTyOrigin {
-        let def_id = opaque_def_id.as_local().unwrap();
+    fn opaque_ty_origin_unchecked(&self, def_id: LocalDefId, span: Span) -> OpaqueTyOrigin {
         let origin = match self.tcx.hir().expect_item(def_id).kind {
             hir::ItemKind::OpaqueTy(hir::OpaqueTy { origin, .. }) => origin,
             ref itemkind => {
-                span_bug!(span, "weird opaque type: {:?}, {:#?}", opaque_def_id, itemkind)
+                span_bug!(span, "weird opaque type: {:?}, {:#?}", def_id, itemkind)
             }
         };
         trace!(?origin);
@@ -557,7 +561,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
             obligations = self.at(&cause, param_env).eq(prev, hidden_ty)?.obligations;
         }
 
-        let item_bounds = tcx.bound_explicit_item_bounds(def_id);
+        let item_bounds = tcx.bound_explicit_item_bounds(def_id.to_def_id());
 
         for predicate in item_bounds.transpose_iter().map(|e| e.map_bound(|(p, _)| *p)) {
             debug!(?predicate);
@@ -579,7 +583,9 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
                     }
                     // Replace all other mentions of the same opaque type with the hidden type,
                     // as the bounds must hold on the hidden type after all.
-                    ty::Opaque(def_id2, substs2) if def_id == def_id2 && substs == substs2 => {
+                    ty::Opaque(def_id2, substs2)
+                        if def_id.to_def_id() == def_id2 && substs == substs2 =>
+                    {
                         hidden_ty
                     }
                     _ => ty,
diff --git a/compiler/rustc_infer/src/infer/region_constraints/mod.rs b/compiler/rustc_infer/src/infer/region_constraints/mod.rs
index c5747ecf702a7..551f398e0c2c4 100644
--- a/compiler/rustc_infer/src/infer/region_constraints/mod.rs
+++ b/compiler/rustc_infer/src/infer/region_constraints/mod.rs
@@ -12,7 +12,7 @@ use rustc_data_structures::intern::Interned;
 use rustc_data_structures::sync::Lrc;
 use rustc_data_structures::undo_log::UndoLogs;
 use rustc_data_structures::unify as ut;
-use rustc_hir::def_id::DefId;
+use rustc_hir::def_id::LocalDefId;
 use rustc_index::vec::IndexVec;
 use rustc_middle::infer::unify_key::{RegionVidKey, UnifiedRegion};
 use rustc_middle::ty::ReStatic;
@@ -533,7 +533,7 @@ impl<'tcx> RegionConstraintCollector<'_, 'tcx> {
 
     pub fn member_constraint(
         &mut self,
-        opaque_type_def_id: DefId,
+        opaque_type_def_id: LocalDefId,
         definition_span: Span,
         hidden_ty: Ty<'tcx>,
         member_region: ty::Region<'tcx>,
diff --git a/compiler/rustc_middle/src/infer/mod.rs b/compiler/rustc_middle/src/infer/mod.rs
index 55e00c4c0d8ef..8b2f9bdfd486b 100644
--- a/compiler/rustc_middle/src/infer/mod.rs
+++ b/compiler/rustc_middle/src/infer/mod.rs
@@ -4,7 +4,7 @@ pub mod unify_key;
 use crate::ty::Region;
 use crate::ty::Ty;
 use rustc_data_structures::sync::Lrc;
-use rustc_hir::def_id::DefId;
+use rustc_hir::def_id::LocalDefId;
 use rustc_span::Span;
 
 /// Requires that `region` must be equal to one of the regions in `choice_regions`.
@@ -16,7 +16,7 @@ use rustc_span::Span;
 #[derive(Debug, Clone, HashStable, TypeFoldable, TypeVisitable, Lift)]
 pub struct MemberConstraint<'tcx> {
     /// The `DefId` of the opaque type causing this constraint: used for error reporting.
-    pub opaque_type_def_id: DefId,
+    pub opaque_type_def_id: LocalDefId,
 
     /// The span where the hidden type was instantiated.
     pub definition_span: Span,
diff --git a/compiler/rustc_middle/src/mir/query.rs b/compiler/rustc_middle/src/mir/query.rs
index 6a6ed3dc728d9..423e84d88cf73 100644
--- a/compiler/rustc_middle/src/mir/query.rs
+++ b/compiler/rustc_middle/src/mir/query.rs
@@ -235,7 +235,7 @@ pub struct BorrowCheckResult<'tcx> {
     /// All the opaque types that are restricted to concrete types
     /// by this function. Unlike the value in `TypeckResults`, this has
     /// unerased regions.
-    pub concrete_opaque_types: VecMap<DefId, OpaqueHiddenType<'tcx>>,
+    pub concrete_opaque_types: VecMap<LocalDefId, OpaqueHiddenType<'tcx>>,
     pub closure_requirements: Option<ClosureRegionRequirements<'tcx>>,
     pub used_mut_upvars: SmallVec<[Field; 8]>,
     pub tainted_by_errors: Option<ErrorGuaranteed>,
diff --git a/compiler/rustc_middle/src/ty/context.rs b/compiler/rustc_middle/src/ty/context.rs
index a594dab2e20a3..0f98d19820e25 100644
--- a/compiler/rustc_middle/src/ty/context.rs
+++ b/compiler/rustc_middle/src/ty/context.rs
@@ -542,7 +542,7 @@ pub struct TypeckResults<'tcx> {
     /// even if they are only set in dead code (which doesn't show up in MIR).
     /// For type-alias-impl-trait, this map is only used to prevent query cycles,
     /// so the hidden types are all `None`.
-    pub concrete_opaque_types: VecMap<DefId, Option<Ty<'tcx>>>,
+    pub concrete_opaque_types: VecMap<LocalDefId, Option<Ty<'tcx>>>,
 
     /// Tracks the minimum captures required for a closure;
     /// see `MinCaptureInformationMap` for more details.
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index 3536d946db279..53919826bf617 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -1108,8 +1108,7 @@ impl<'tcx> InstantiatedPredicates<'tcx> {
 #[derive(Copy, Clone, Debug, PartialEq, Eq, HashStable, TyEncodable, TyDecodable, Lift)]
 #[derive(TypeFoldable, TypeVisitable)]
 pub struct OpaqueTypeKey<'tcx> {
-    // FIXME(oli-obk): make this a LocalDefId
-    pub def_id: DefId,
+    pub def_id: LocalDefId,
     pub substs: SubstsRef<'tcx>,
 }
 
diff --git a/compiler/rustc_middle/src/ty/sty.rs b/compiler/rustc_middle/src/ty/sty.rs
index d663f1a3ec6e7..9f622ad6cd2a1 100644
--- a/compiler/rustc_middle/src/ty/sty.rs
+++ b/compiler/rustc_middle/src/ty/sty.rs
@@ -1707,13 +1707,6 @@ impl<'tcx> Ty<'tcx> {
         }
     }
 
-    pub fn expect_opaque_type(self) -> ty::OpaqueTypeKey<'tcx> {
-        match *self.kind() {
-            Opaque(def_id, substs) => ty::OpaqueTypeKey { def_id, substs },
-            _ => bug!("`expect_opaque_type` called on non-opaque type: {}", self),
-        }
-    }
-
     pub fn simd_size_and_type(self, tcx: TyCtxt<'tcx>) -> (u64, Ty<'tcx>) {
         match self.kind() {
             Adt(def, substs) => {
diff --git a/compiler/rustc_typeck/src/check/fn_ctxt/_impl.rs b/compiler/rustc_typeck/src/check/fn_ctxt/_impl.rs
index d33b5b2140362..d079aeb4801ca 100644
--- a/compiler/rustc_typeck/src/check/fn_ctxt/_impl.rs
+++ b/compiler/rustc_typeck/src/check/fn_ctxt/_impl.rs
@@ -763,12 +763,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // src/test/ui/impl-trait/hidden-type-is-opaque-2.rs for examples that hit this path.
         if formal_ret.has_infer_types() {
             for ty in ret_ty.walk() {
-                if let ty::subst::GenericArgKind::Type(ty) = ty.unpack() {
-                    if let ty::Opaque(def_id, _) = *ty.kind() {
-                        if self.infcx.opaque_type_origin(def_id, DUMMY_SP).is_some() {
-                            return None;
-                        }
-                    }
+                if let ty::subst::GenericArgKind::Type(ty) = ty.unpack()
+                    && let ty::Opaque(def_id, _) = *ty.kind()
+                    && let Some(def_id) = def_id.as_local()
+                    && self.infcx.opaque_type_origin(def_id, DUMMY_SP).is_some() {
+                    return None;
                 }
             }
         }
diff --git a/compiler/rustc_typeck/src/check/writeback.rs b/compiler/rustc_typeck/src/check/writeback.rs
index 0cbb0e25d0d42..23ac638b2f430 100644
--- a/compiler/rustc_typeck/src/check/writeback.rs
+++ b/compiler/rustc_typeck/src/check/writeback.rs
@@ -4,6 +4,7 @@
 
 use crate::check::FnCtxt;
 
+use hir::def_id::LocalDefId;
 use rustc_data_structures::stable_map::FxHashMap;
 use rustc_errors::ErrorGuaranteed;
 use rustc_hir as hir;
@@ -509,13 +510,13 @@ impl<'cx, 'tcx> WritebackCx<'cx, 'tcx> {
                 hir::OpaqueTyOrigin::FnReturn(_) | hir::OpaqueTyOrigin::AsyncFn(_) => {
                     let ty = self.resolve(decl.hidden_type.ty, &decl.hidden_type.span);
                     struct RecursionChecker {
-                        def_id: DefId,
+                        def_id: LocalDefId,
                     }
                     impl<'tcx> ty::TypeVisitor<'tcx> for RecursionChecker {
                         type BreakTy = ();
                         fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
                             if let ty::Opaque(def_id, _) = *t.kind() {
-                                if def_id == self.def_id {
+                                if def_id == self.def_id.to_def_id() {
                                     return ControlFlow::Break(());
                                 }
                             }
diff --git a/compiler/rustc_typeck/src/collect/type_of.rs b/compiler/rustc_typeck/src/collect/type_of.rs
index f942a4fb53a26..faa4f3700bba8 100644
--- a/compiler/rustc_typeck/src/collect/type_of.rs
+++ b/compiler/rustc_typeck/src/collect/type_of.rs
@@ -342,7 +342,7 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: DefId) -> Ty<'_> {
                     let concrete_ty = tcx
                         .mir_borrowck(owner)
                         .concrete_opaque_types
-                        .get(&def_id.to_def_id())
+                        .get(&def_id)
                         .copied()
                         .map(|concrete| concrete.ty)
                         .unwrap_or_else(|| {
@@ -353,7 +353,7 @@ pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: DefId) -> Ty<'_> {
                                 // the `concrete_opaque_types` table.
                                 tcx.ty_error()
                             } else {
-                                table.concrete_opaque_types.get(&def_id.to_def_id()).copied().unwrap_or_else(|| {
+                                table.concrete_opaque_types.get(&def_id).copied().unwrap_or_else(|| {
                                     // We failed to resolve the opaque type or it
                                     // resolves to itself. We interpret this as the
                                     // no values of the hidden type ever being constructed,
@@ -526,7 +526,7 @@ fn find_opaque_ty_constraints(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Ty<'_> {
         tcx: TyCtxt<'tcx>,
 
         /// def_id of the opaque type whose defining uses are being checked
-        def_id: DefId,
+        def_id: LocalDefId,
 
         /// as we walk the defining uses, we are checking that all of them
         /// define the same hidden type. This variable is set to `Some`
@@ -602,7 +602,7 @@ fn find_opaque_ty_constraints(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Ty<'_> {
         fn visit_item(&mut self, it: &'tcx Item<'tcx>) {
             trace!(?it.def_id);
             // The opaque type itself or its children are not within its reveal scope.
-            if it.def_id.to_def_id() != self.def_id {
+            if it.def_id != self.def_id {
                 self.check(it.def_id);
                 intravisit::walk_item(self, it);
             }
@@ -610,7 +610,7 @@ fn find_opaque_ty_constraints(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Ty<'_> {
         fn visit_impl_item(&mut self, it: &'tcx ImplItem<'tcx>) {
             trace!(?it.def_id);
             // The opaque type itself or its children are not within its reveal scope.
-            if it.def_id.to_def_id() != self.def_id {
+            if it.def_id != self.def_id {
                 self.check(it.def_id);
                 intravisit::walk_impl_item(self, it);
             }
@@ -624,7 +624,7 @@ fn find_opaque_ty_constraints(tcx: TyCtxt<'_>, def_id: LocalDefId) -> Ty<'_> {
 
     let hir_id = tcx.hir().local_def_id_to_hir_id(def_id);
     let scope = tcx.hir().get_defining_scope(hir_id);
-    let mut locator = ConstraintLocator { def_id: def_id.to_def_id(), tcx, found: None };
+    let mut locator = ConstraintLocator { def_id: def_id, tcx, found: None };
 
     debug!(?scope);
 
diff --git a/library/alloc/src/alloc.rs b/library/alloc/src/alloc.rs
index 649aeb0890dc0..efdc86bf57a8a 100644
--- a/library/alloc/src/alloc.rs
+++ b/library/alloc/src/alloc.rs
@@ -70,11 +70,14 @@ pub use std::alloc::Global;
 /// # Examples
 ///
 /// ```
-/// use std::alloc::{alloc, dealloc, Layout};
+/// use std::alloc::{alloc, dealloc, handle_alloc_error, Layout};
 ///
 /// unsafe {
 ///     let layout = Layout::new::<u16>();
 ///     let ptr = alloc(layout);
+///     if ptr.is_null() {
+///         handle_alloc_error(layout);
+///     }
 ///
 ///     *(ptr as *mut u16) = 42;
 ///     assert_eq!(*(ptr as *mut u16), 42);
diff --git a/library/core/src/mem/mod.rs b/library/core/src/mem/mod.rs
index ecd2b75ae4427..66af491607435 100644
--- a/library/core/src/mem/mod.rs
+++ b/library/core/src/mem/mod.rs
@@ -1040,6 +1040,8 @@ pub fn copy<T: Copy>(x: &T) -> T {
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_const_unstable(feature = "const_transmute_copy", issue = "83165")]
 pub const unsafe fn transmute_copy<T, U>(src: &T) -> U {
+    assert!(size_of::<T>() >= size_of::<U>(), "cannot transmute_copy if U is larger than T");
+
     // If U has a higher alignment requirement, src might not be suitably aligned.
     if align_of::<U>() > align_of::<T>() {
         // SAFETY: `src` is a reference which is guaranteed to be valid for reads.
diff --git a/library/core/tests/mem.rs b/library/core/tests/mem.rs
index 3b13dc0832fa4..6856d1a1f51ae 100644
--- a/library/core/tests/mem.rs
+++ b/library/core/tests/mem.rs
@@ -97,6 +97,46 @@ fn test_transmute_copy() {
     assert_eq!(1, unsafe { transmute_copy(&1) });
 }
 
+#[test]
+fn test_transmute_copy_shrink() {
+    assert_eq!(0_u8, unsafe { transmute_copy(&0_u64) });
+}
+
+#[test]
+fn test_transmute_copy_unaligned() {
+    #[repr(C)]
+    #[derive(Default)]
+    struct Unaligned {
+        a: u8,
+        b: [u8; 8],
+    }
+
+    let u = Unaligned::default();
+    assert_eq!(0_u64, unsafe { transmute_copy(&u.b) });
+}
+
+#[test]
+#[cfg(panic = "unwind")]
+fn test_transmute_copy_grow_panics() {
+    use std::panic;
+
+    let err = panic::catch_unwind(panic::AssertUnwindSafe(|| unsafe {
+        let _unused: u64 = transmute_copy(&1_u8);
+    }));
+
+    match err {
+        Ok(_) => unreachable!(),
+        Err(payload) => {
+            payload
+                .downcast::<&'static str>()
+                .and_then(|s| {
+                    if *s == "cannot transmute_copy if U is larger than T" { Ok(s) } else { Err(s) }
+                })
+                .unwrap_or_else(|p| panic::resume_unwind(p));
+        }
+    }
+}
+
 #[test]
 #[allow(dead_code)]
 fn test_discriminant_send_sync() {
diff --git a/library/std/src/fs/tests.rs b/library/std/src/fs/tests.rs
index e8d0132f4b98c..d8806b6ec60bf 100644
--- a/library/std/src/fs/tests.rs
+++ b/library/std/src/fs/tests.rs
@@ -1534,3 +1534,17 @@ fn read_large_dir() {
         entry.unwrap();
     }
 }
+
+/// Test the fallback for getting the metadata of files like hiberfil.sys that
+/// Windows holds a special lock on, preventing normal means of querying
+/// metadata. See #96980.
+#[test]
+#[cfg(windows)]
+fn hiberfil_sys() {
+    let hiberfil = Path::new(r"C:\hiberfil.sys");
+
+    assert_eq!(true, hiberfil.try_exists().unwrap());
+    fs::symlink_metadata(hiberfil).unwrap();
+    fs::metadata(hiberfil).unwrap();
+    assert_eq!(true, hiberfil.exists());
+}
diff --git a/library/std/src/sys/windows/fs.rs b/library/std/src/sys/windows/fs.rs
index e9b1006907741..4d3162f125462 100644
--- a/library/std/src/sys/windows/fs.rs
+++ b/library/std/src/sys/windows/fs.rs
@@ -155,22 +155,7 @@ impl DirEntry {
     }
 
     pub fn metadata(&self) -> io::Result<FileAttr> {
-        Ok(FileAttr {
-            attributes: self.data.dwFileAttributes,
-            creation_time: self.data.ftCreationTime,
-            last_access_time: self.data.ftLastAccessTime,
-            last_write_time: self.data.ftLastWriteTime,
-            file_size: ((self.data.nFileSizeHigh as u64) << 32) | (self.data.nFileSizeLow as u64),
-            reparse_tag: if self.data.dwFileAttributes & c::FILE_ATTRIBUTE_REPARSE_POINT != 0 {
-                // reserved unless this is a reparse point
-                self.data.dwReserved0
-            } else {
-                0
-            },
-            volume_serial_number: None,
-            number_of_links: None,
-            file_index: None,
-        })
+        Ok(self.data.into())
     }
 }
 
@@ -879,6 +864,26 @@ impl FileAttr {
         self.file_index
     }
 }
+impl From<c::WIN32_FIND_DATAW> for FileAttr {
+    fn from(wfd: c::WIN32_FIND_DATAW) -> Self {
+        FileAttr {
+            attributes: wfd.dwFileAttributes,
+            creation_time: wfd.ftCreationTime,
+            last_access_time: wfd.ftLastAccessTime,
+            last_write_time: wfd.ftLastWriteTime,
+            file_size: ((wfd.nFileSizeHigh as u64) << 32) | (wfd.nFileSizeLow as u64),
+            reparse_tag: if wfd.dwFileAttributes & c::FILE_ATTRIBUTE_REPARSE_POINT != 0 {
+                // reserved unless this is a reparse point
+                wfd.dwReserved0
+            } else {
+                0
+            },
+            volume_serial_number: None,
+            number_of_links: None,
+            file_index: None,
+        }
+    }
+}
 
 fn to_u64(ft: &c::FILETIME) -> u64 {
     (ft.dwLowDateTime as u64) | ((ft.dwHighDateTime as u64) << 32)
@@ -1145,22 +1150,73 @@ pub fn link(_original: &Path, _link: &Path) -> io::Result<()> {
 }
 
 pub fn stat(path: &Path) -> io::Result<FileAttr> {
-    let mut opts = OpenOptions::new();
-    // No read or write permissions are necessary
-    opts.access_mode(0);
-    // This flag is so we can open directories too
-    opts.custom_flags(c::FILE_FLAG_BACKUP_SEMANTICS);
-    let file = File::open(path, &opts)?;
-    file.file_attr()
+    metadata(path, ReparsePoint::Follow)
 }
 
 pub fn lstat(path: &Path) -> io::Result<FileAttr> {
+    metadata(path, ReparsePoint::Open)
+}
+
+#[repr(u32)]
+#[derive(Clone, Copy, PartialEq, Eq)]
+enum ReparsePoint {
+    Follow = 0,
+    Open = c::FILE_FLAG_OPEN_REPARSE_POINT,
+}
+impl ReparsePoint {
+    fn as_flag(self) -> u32 {
+        self as u32
+    }
+}
+
+fn metadata(path: &Path, reparse: ReparsePoint) -> io::Result<FileAttr> {
     let mut opts = OpenOptions::new();
     // No read or write permissions are necessary
     opts.access_mode(0);
-    opts.custom_flags(c::FILE_FLAG_BACKUP_SEMANTICS | c::FILE_FLAG_OPEN_REPARSE_POINT);
-    let file = File::open(path, &opts)?;
-    file.file_attr()
+    opts.custom_flags(c::FILE_FLAG_BACKUP_SEMANTICS | reparse.as_flag());
+
+    // Attempt to open the file normally.
+    // If that fails with `ERROR_SHARING_VIOLATION` then retry using `FindFirstFileW`.
+    // If the fallback fails for any reason we return the original error.
+    match File::open(path, &opts) {
+        Ok(file) => file.file_attr(),
+        Err(e) if e.raw_os_error() == Some(c::ERROR_SHARING_VIOLATION as _) => {
+            // `ERROR_SHARING_VIOLATION` will almost never be returned.
+            // Usually if a file is locked you can still read some metadata.
+            // However, there are special system files, such as
+            // `C:\hiberfil.sys`, that are locked in a way that denies even that.
+            unsafe {
+                let path = maybe_verbatim(path)?;
+
+                // `FindFirstFileW` accepts wildcard file names.
+                // Fortunately wildcards are not valid file names and
+                // `ERROR_SHARING_VIOLATION` means the file exists (but is locked)
+                // therefore it's safe to assume the file name given does not
+                // include wildcards.
+                let mut wfd = mem::zeroed();
+                let handle = c::FindFirstFileW(path.as_ptr(), &mut wfd);
+
+                if handle == c::INVALID_HANDLE_VALUE {
+                    // This can fail if the user does not have read access to the
+                    // directory.
+                    Err(e)
+                } else {
+                    // We no longer need the find handle.
+                    c::FindClose(handle);
+
+                    // `FindFirstFileW` reads the cached file information from the
+                    // directory. The downside is that this metadata may be outdated.
+                    let attrs = FileAttr::from(wfd);
+                    if reparse == ReparsePoint::Follow && attrs.file_type().is_symlink() {
+                        Err(e)
+                    } else {
+                        Ok(attrs)
+                    }
+                }
+            }
+        }
+        Err(e) => Err(e),
+    }
 }
 
 pub fn set_perm(p: &Path, perm: FilePermissions) -> io::Result<()> {