Auto merge of #107811 - matthiaskrgr:rollup-rpjzshk, r=matthiaskrgr

Rollup of 8 pull requests

Successful merges:

 - #105641 (Implement cursors for BTreeMap)
 - #107271 (Treat Drop as a rmw operation)
 - #107710 (Update strip-ansi-escapes and vte)
 - #107758 (Change `arena_cache` to not alter the declared query result)
 - #107777 (Make `derive_const` derive properly const-if-const impls)
 - #107780 (Rename `replace_bound_vars_with_*` to `instantiate_binder_with_*`)
 - #107793 (Add missing tracking issue for `RawOsError`)
 - #107807 (Fix small debug typo)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

Cargo.lock

@@ -127,6 +127,12 @@ version = "1.0.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8f8cb5d814eb646a863c4f24978cff2880c4be96ad8cde2c0f0678732902e271"
 
+[[package]]
+name = "arrayvec"
+version = "0.5.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "23b62fc65de8e4e7f52534fb52b0f3ed04746ae267519eef2a83941e8085068b"
+
 [[package]]
 name = "arrayvec"
 version = "0.7.0"
@@ -791,7 +797,7 @@ dependencies = [
 name = "clippy_utils"
 version = "0.1.69"
 dependencies = [
- "arrayvec",
+ "arrayvec 0.7.0",
  "if_chain",
  "itertools",
  "rustc-semver",
@@ -3912,7 +3918,7 @@ dependencies = [
 name = "rustc_data_structures"
 version = "0.0.0"
 dependencies = [
- "arrayvec",
+ "arrayvec 0.7.0",
  "bitflags",
  "cfg-if",
  "ena",
@@ -4169,7 +4175,7 @@ dependencies = [
 name = "rustc_index"
 version = "0.0.0"
 dependencies = [
- "arrayvec",
+ "arrayvec 0.7.0",
  "rustc_macros",
  "rustc_serialize",
  "smallvec",
@@ -4866,7 +4872,7 @@ dependencies = [
 name = "rustdoc"
 version = "0.0.0"
 dependencies = [
- "arrayvec",
+ "arrayvec 0.7.0",
  "askama",
  "expect-test",
  "itertools",
@@ -5375,9 +5381,9 @@ dependencies = [
 
 [[package]]
 name = "strip-ansi-escapes"
-version = "0.1.0"
+version = "0.1.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9d63676e2abafa709460982ddc02a3bb586b6d15a49b75c212e06edd3933acee"
+checksum = "011cbb39cf7c1f62871aea3cc46e5817b0937b49e9447370c93cacbe93a766d8"
 dependencies = [
  "vte",
 ]
@@ -6089,9 +6095,9 @@ checksum = "05e42f7c18b8f902290b009cde6d651262f956c98bc51bca4cd1d511c9cd85c7"
 
 [[package]]
 name = "utf8parse"
-version = "0.1.1"
+version = "0.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8772a4ccbb4e89959023bc5b7cb8623a795caa7092d99f3aa9501b9484d4557d"
+checksum = "936e4b492acfd135421d8dca4b1aa80a7bfc26e702ef3af710e0752684df5372"
 
 [[package]]
 name = "uuid"
@@ -6122,11 +6128,23 @@ checksum = "49874b5167b65d7193b8aba1567f5c7d93d001cafc34600cee003eda787e483f"
 
 [[package]]
 name = "vte"
-version = "0.3.3"
+version = "0.10.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "4f42f536e22f7fcbb407639765c8fd78707a33109301f834a594758bedd6e8cf"
+checksum = "6cbce692ab4ca2f1f3047fcf732430249c0e971bfdd2b234cf2c47ad93af5983"
 dependencies = [
+ "arrayvec 0.5.2",
  "utf8parse",
+ "vte_generate_state_changes",
+]
+
+[[package]]
+name = "vte_generate_state_changes"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d257817081c7dffcdbab24b9e62d2def62e2ff7d00b1c20062551e6cccc145ff"
+dependencies = [
+ "proc-macro2",
+ "quote",
 ]
 
 [[package]]

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -1567,8 +1567,18 @@ impl<'a> State<'a> {
 
             match bound {
                 GenericBound::Trait(tref, modifier) => {
-                    if modifier == &TraitBoundModifier::Maybe {
+                    match modifier {
-                        self.word("?");
+                        TraitBoundModifier::None => {}
+                        TraitBoundModifier::Maybe => {
+                            self.word("?");
+                        }
+                        TraitBoundModifier::MaybeConst => {
+                            self.word_space("~const");
+                        }
+                        TraitBoundModifier::MaybeConstMaybe => {
+                            self.word_space("~const");
+                            self.word("?");
+                        }
                     }
                     self.print_poly_trait_ref(tref);
                 }

compiler/rustc_borrowck/src/diagnostics/mod.rs

@@ -1139,7 +1139,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                         if let ty::Adt(def, substs) = ty.kind()
                             && Some(def.did()) == tcx.lang_items().pin_type()
                             && let ty::Ref(_, _, hir::Mutability::Mut) = substs.type_at(0).kind()
-                            && let self_ty = infcx.replace_bound_vars_with_fresh_vars(
+                            && let self_ty = infcx.instantiate_binder_with_fresh_vars(
                                 fn_call_span,
                                 LateBoundRegionConversionTime::FnCall,
                                 tcx.fn_sig(method_did).subst(tcx, method_substs).input(0),

compiler/rustc_borrowck/src/type_check/input_output.rs

@@ -38,7 +38,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
         // so that they represent the view from "inside" the closure.
         let user_provided_sig = self
             .instantiate_canonical_with_fresh_inference_vars(body.span, &user_provided_poly_sig);
-        let user_provided_sig = self.infcx.replace_bound_vars_with_fresh_vars(
+        let user_provided_sig = self.infcx.instantiate_binder_with_fresh_vars(
             body.span,
             LateBoundRegionConversionTime::FnCall,
             user_provided_sig,

compiler/rustc_builtin_macros/src/deriving/debug.rs

@@ -153,7 +153,10 @@ fn show_substructure(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>
         let path_debug = cx.path_global(span, cx.std_path(&[sym::fmt, sym::Debug]));
         let ty_dyn_debug = cx.ty(
             span,
-            ast::TyKind::TraitObject(vec![cx.trait_bound(path_debug)], ast::TraitObjectSyntax::Dyn),
+            ast::TyKind::TraitObject(
+                vec![cx.trait_bound(path_debug, false)],
+                ast::TraitObjectSyntax::Dyn,
+            ),
         );
         let ty_slice = cx.ty(
             span,

compiler/rustc_builtin_macros/src/deriving/generic/mod.rs

@@ -605,18 +605,26 @@ impl<'a> TraitDef<'a> {
                     let bounds: Vec<_> = self
                         .additional_bounds
                         .iter()
-                        .map(|p| cx.trait_bound(p.to_path(cx, self.span, type_ident, generics)))
+                        .map(|p| {
+                            cx.trait_bound(
+                                p.to_path(cx, self.span, type_ident, generics),
+                                self.is_const,
+                            )
+                        })
                         .chain(
                             // Add a bound for the current trait.
                             self.skip_path_as_bound
                                 .not()
-                                .then(|| cx.trait_bound(trait_path.clone())),
+                                .then(|| cx.trait_bound(trait_path.clone(), self.is_const)),
                         )
                         .chain({
                             // Add a `Copy` bound if required.
                             if is_packed && self.needs_copy_as_bound_if_packed {
                                 let p = deriving::path_std!(marker::Copy);
-                                Some(cx.trait_bound(p.to_path(cx, self.span, type_ident, generics)))
+                                Some(cx.trait_bound(
+                                    p.to_path(cx, self.span, type_ident, generics),
+                                    self.is_const,
+                                ))
                             } else {
                                 None
                             }
@@ -694,18 +702,24 @@ impl<'a> TraitDef<'a> {
                         let mut bounds: Vec<_> = self
                             .additional_bounds
                             .iter()
-                            .map(|p| cx.trait_bound(p.to_path(cx, self.span, type_ident, generics)))
+                            .map(|p| {
+                                cx.trait_bound(
+                                    p.to_path(cx, self.span, type_ident, generics),
+                                    self.is_const,
+                                )
+                            })
                             .collect();
 
                         // Require the current trait.
-                        bounds.push(cx.trait_bound(trait_path.clone()));
+                        bounds.push(cx.trait_bound(trait_path.clone(), self.is_const));
 
                         // Add a `Copy` bound if required.
                         if is_packed && self.needs_copy_as_bound_if_packed {
                             let p = deriving::path_std!(marker::Copy);
-                            bounds.push(
+                            bounds.push(cx.trait_bound(
-                                cx.trait_bound(p.to_path(cx, self.span, type_ident, generics)),
+                                p.to_path(cx, self.span, type_ident, generics),
-                            );
+                                self.is_const,
+                            ));
                         }
 
                         let predicate = ast::WhereBoundPredicate {

compiler/rustc_builtin_macros/src/deriving/generic/ty.rs

@@ -154,7 +154,7 @@ fn mk_ty_param(
         .iter()
         .map(|b| {
             let path = b.to_path(cx, span, self_ident, self_generics);
-            cx.trait_bound(path)
+            cx.trait_bound(path, false)
         })
         .collect();
     cx.typaram(span, Ident::new(name, span), bounds, None)

compiler/rustc_expand/src/build.rs

@@ -131,10 +131,14 @@ impl<'a> ExtCtxt<'a> {
         }
     }
 
-    pub fn trait_bound(&self, path: ast::Path) -> ast::GenericBound {
+    pub fn trait_bound(&self, path: ast::Path, is_const: bool) -> ast::GenericBound {
         ast::GenericBound::Trait(
             self.poly_trait_ref(path.span, path),
-            ast::TraitBoundModifier::None,
+            if is_const {
+                ast::TraitBoundModifier::MaybeConst
+            } else {
+                ast::TraitBoundModifier::None
+            },
         )
     }
 

compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -246,7 +246,7 @@ fn compare_method_predicate_entailment<'tcx>(
 
     let mut wf_tys = FxIndexSet::default();
 
-    let unnormalized_impl_sig = infcx.replace_bound_vars_with_fresh_vars(
+    let unnormalized_impl_sig = infcx.instantiate_binder_with_fresh_vars(
         impl_m_span,
         infer::HigherRankedType,
         tcx.fn_sig(impl_m.def_id).subst_identity(),
@@ -640,7 +640,7 @@ pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>(
     let impl_sig = ocx.normalize(
         &norm_cause,
         param_env,
-        infcx.replace_bound_vars_with_fresh_vars(
+        infcx.instantiate_binder_with_fresh_vars(
             return_span,
             infer::HigherRankedType,
             tcx.fn_sig(impl_m.def_id).subst_identity(),

compiler/rustc_hir_typeck/src/callee.rs

@@ -156,7 +156,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 // fnmut vs fnonce. If so, we have to defer further processing.
                 if self.closure_kind(substs).is_none() {
                     let closure_sig = substs.as_closure().sig();
-                    let closure_sig = self.replace_bound_vars_with_fresh_vars(
+                    let closure_sig = self.instantiate_binder_with_fresh_vars(
                         call_expr.span,
                         infer::FnCall,
                         closure_sig,
@@ -437,7 +437,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // renormalize the associated types at this point, since they
         // previously appeared within a `Binder<>` and hence would not
         // have been normalized before.
-        let fn_sig = self.replace_bound_vars_with_fresh_vars(call_expr.span, infer::FnCall, fn_sig);
+        let fn_sig = self.instantiate_binder_with_fresh_vars(call_expr.span, infer::FnCall, fn_sig);
         let fn_sig = self.normalize(call_expr.span, fn_sig);
 
         // Call the generic checker.

compiler/rustc_hir_typeck/src/closure.rs

@@ -544,7 +544,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             )
             .map(|(hir_ty, &supplied_ty)| {
                 // Instantiate (this part of..) S to S', i.e., with fresh variables.
-                self.replace_bound_vars_with_fresh_vars(
+                self.instantiate_binder_with_fresh_vars(
                     hir_ty.span,
                     LateBoundRegionConversionTime::FnCall,
                     // (*) binder moved to here
@@ -566,7 +566,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 all_obligations.extend(obligations);
             }
 
-            let supplied_output_ty = self.replace_bound_vars_with_fresh_vars(
+            let supplied_output_ty = self.instantiate_binder_with_fresh_vars(
                 decl.output.span(),
                 LateBoundRegionConversionTime::FnCall,
                 supplied_sig.output(),

compiler/rustc_hir_typeck/src/expr.rs

@@ -568,7 +568,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     // placeholder lifetimes with probing, we just replace higher lifetimes
                     // with fresh vars.
                     let span = args.get(i).map(|a| a.span).unwrap_or(expr.span);
-                    let input = self.replace_bound_vars_with_fresh_vars(
+                    let input = self.instantiate_binder_with_fresh_vars(
                         span,
                         infer::LateBoundRegionConversionTime::FnCall,
                         fn_sig.input(i),
@@ -586,7 +586,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             // Also, as we just want to check sizedness, instead of introducing
             // placeholder lifetimes with probing, we just replace higher lifetimes
             // with fresh vars.
-            let output = self.replace_bound_vars_with_fresh_vars(
+            let output = self.instantiate_binder_with_fresh_vars(
                 expr.span,
                 infer::LateBoundRegionConversionTime::FnCall,
                 fn_sig.output(),

compiler/rustc_hir_typeck/src/fn_ctxt/mod.rs

@@ -289,7 +289,7 @@ impl<'a, 'tcx> AstConv<'tcx> for FnCtxt<'a, 'tcx> {
         item_segment: &hir::PathSegment<'_>,
         poly_trait_ref: ty::PolyTraitRef<'tcx>,
     ) -> Ty<'tcx> {
-        let trait_ref = self.replace_bound_vars_with_fresh_vars(
+        let trait_ref = self.instantiate_binder_with_fresh_vars(
             span,
             infer::LateBoundRegionConversionTime::AssocTypeProjection(item_def_id),
             poly_trait_ref,

compiler/rustc_hir_typeck/src/method/confirm.rs

@@ -262,7 +262,7 @@ impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
                     let original_poly_trait_ref = principal.with_self_ty(this.tcx, object_ty);
                     let upcast_poly_trait_ref = this.upcast(original_poly_trait_ref, trait_def_id);
                     let upcast_trait_ref =
-                        this.replace_bound_vars_with_fresh_vars(upcast_poly_trait_ref);
+                        this.instantiate_binder_with_fresh_vars(upcast_poly_trait_ref);
                     debug!(
                         "original_poly_trait_ref={:?} upcast_trait_ref={:?} target_trait={:?}",
                         original_poly_trait_ref, upcast_trait_ref, trait_def_id
@@ -285,7 +285,7 @@ impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
             probe::WhereClausePick(poly_trait_ref) => {
                 // Where clauses can have bound regions in them. We need to instantiate
                 // those to convert from a poly-trait-ref to a trait-ref.
-                self.replace_bound_vars_with_fresh_vars(poly_trait_ref).substs
+                self.instantiate_binder_with_fresh_vars(poly_trait_ref).substs
             }
         }
     }
@@ -506,7 +506,7 @@ impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
         let sig = self.tcx.fn_sig(def_id).subst(self.tcx, all_substs);
         debug!("type scheme substituted, sig={:?}", sig);
 
-        let sig = self.replace_bound_vars_with_fresh_vars(sig);
+        let sig = self.instantiate_binder_with_fresh_vars(sig);
         debug!("late-bound lifetimes from method instantiated, sig={:?}", sig);
 
         (sig, method_predicates)
@@ -625,10 +625,10 @@ impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
         upcast_trait_refs.into_iter().next().unwrap()
     }
 
-    fn replace_bound_vars_with_fresh_vars<T>(&self, value: ty::Binder<'tcx, T>) -> T
+    fn instantiate_binder_with_fresh_vars<T>(&self, value: ty::Binder<'tcx, T>) -> T
     where
         T: TypeFoldable<'tcx> + Copy,
     {
-        self.fcx.replace_bound_vars_with_fresh_vars(self.span, infer::FnCall, value)
+        self.fcx.instantiate_binder_with_fresh_vars(self.span, infer::FnCall, value)
     }
 }

compiler/rustc_hir_typeck/src/method/mod.rs

@@ -401,7 +401,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // with bound regions.
         let fn_sig = tcx.fn_sig(def_id).subst(self.tcx, substs);
         let fn_sig =
-            self.replace_bound_vars_with_fresh_vars(obligation.cause.span, infer::FnCall, fn_sig);
+            self.instantiate_binder_with_fresh_vars(obligation.cause.span, infer::FnCall, fn_sig);
 
         let InferOk { value, obligations: o } =
             self.at(&obligation.cause, self.param_env).normalize(fn_sig);

compiler/rustc_hir_typeck/src/method/probe.rs

@@ -924,7 +924,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
             ty::AssocKind::Fn => self.probe(|_| {
                 let substs = self.fresh_substs_for_item(self.span, method.def_id);
                 let fty = self.tcx.fn_sig(method.def_id).subst(self.tcx, substs);
-                let fty = self.replace_bound_vars_with_fresh_vars(self.span, infer::FnCall, fty);
+                let fty = self.instantiate_binder_with_fresh_vars(self.span, infer::FnCall, fty);
 
                 if let Some(self_ty) = self_ty {
                     if self

compiler/rustc_infer/src/infer/equate.rs

@@ -129,7 +129,7 @@ impl<'tcx> TypeRelation<'tcx> for Equate<'_, '_, 'tcx> {
                 let a_types = infcx.tcx.anonymize_bound_vars(a_types);
                 let b_types = infcx.tcx.anonymize_bound_vars(b_types);
                 if a_types.bound_vars() == b_types.bound_vars() {
-                    let (a_types, b_types) = infcx.replace_bound_vars_with_placeholders(
+                    let (a_types, b_types) = infcx.instantiate_binder_with_placeholders(
                         a_types.map_bound(|a_types| (a_types, b_types.skip_binder())),
                     );
                     for (a, b) in std::iter::zip(a_types, b_types) {

compiler/rustc_infer/src/infer/higher_ranked/mod.rs

@@ -38,13 +38,13 @@ impl<'a, 'tcx> CombineFields<'a, 'tcx> {
         // First, we instantiate each bound region in the supertype with a
         // fresh placeholder region. Note that this automatically creates
         // a new universe if needed.
-        let sup_prime = self.infcx.replace_bound_vars_with_placeholders(sup);
+        let sup_prime = self.infcx.instantiate_binder_with_placeholders(sup);
 
         // Next, we instantiate each bound region in the subtype
         // with a fresh region variable. These region variables --
         // but no other pre-existing region variables -- can name
         // the placeholders.
-        let sub_prime = self.infcx.replace_bound_vars_with_fresh_vars(span, HigherRankedType, sub);
+        let sub_prime = self.infcx.instantiate_binder_with_fresh_vars(span, HigherRankedType, sub);
 
         debug!("a_prime={:?}", sub_prime);
         debug!("b_prime={:?}", sup_prime);
@@ -70,7 +70,7 @@ impl<'tcx> InferCtxt<'tcx> {
     ///
     /// [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/traits/hrtb.html
     #[instrument(level = "debug", skip(self), ret)]
-    pub fn replace_bound_vars_with_placeholders<T>(&self, binder: ty::Binder<'tcx, T>) -> T
+    pub fn instantiate_binder_with_placeholders<T>(&self, binder: ty::Binder<'tcx, T>) -> T
     where
         T: TypeFoldable<'tcx> + Copy,
     {

compiler/rustc_infer/src/infer/mod.rs

@@ -995,7 +995,7 @@ impl<'tcx> InferCtxt<'tcx> {
 
         Ok(self.commit_if_ok(|_snapshot| {
             let ty::SubtypePredicate { a_is_expected, a, b } =
-                self.replace_bound_vars_with_placeholders(predicate);
+                self.instantiate_binder_with_placeholders(predicate);
 
             let ok = self.at(cause, param_env).sub_exp(a_is_expected, a, b)?;
 
@@ -1008,7 +1008,7 @@ impl<'tcx> InferCtxt<'tcx> {
         cause: &traits::ObligationCause<'tcx>,
         predicate: ty::PolyRegionOutlivesPredicate<'tcx>,
     ) {
-        let ty::OutlivesPredicate(r_a, r_b) = self.replace_bound_vars_with_placeholders(predicate);
+        let ty::OutlivesPredicate(r_a, r_b) = self.instantiate_binder_with_placeholders(predicate);
         let origin =
             SubregionOrigin::from_obligation_cause(cause, || RelateRegionParamBound(cause.span));
         self.sub_regions(origin, r_b, r_a); // `b : a` ==> `a <= b`
@@ -1447,7 +1447,14 @@ impl<'tcx> InferCtxt<'tcx> {
         value
     }
 
-    pub fn replace_bound_vars_with_fresh_vars<T>(
+    // Instantiates the bound variables in a given binder with fresh inference
+    // variables in the current universe.
+    //
+    // Use this method if you'd like to find some substitution of the binder's
+    // variables (e.g. during a method call). If there isn't a [`LateBoundRegionConversionTime`]
+    // that corresponds to your use case, consider whether or not you should
+    // use [`InferCtxt::instantiate_binder_with_placeholders`] instead.
+    pub fn instantiate_binder_with_fresh_vars<T>(
         &self,
         span: Span,
         lbrct: LateBoundRegionConversionTime,

compiler/rustc_infer/src/infer/sub.rs

@@ -161,7 +161,7 @@ impl<'tcx> TypeRelation<'tcx> for Sub<'_, '_, 'tcx> {
                 let a_types = infcx.tcx.anonymize_bound_vars(a_types);
                 let b_types = infcx.tcx.anonymize_bound_vars(b_types);
                 if a_types.bound_vars() == b_types.bound_vars() {
-                    let (a_types, b_types) = infcx.replace_bound_vars_with_placeholders(
+                    let (a_types, b_types) = infcx.instantiate_binder_with_placeholders(
                         a_types.map_bound(|a_types| (a_types, b_types.skip_binder())),
                     );
                     for (a, b) in std::iter::zip(a_types, b_types) {

compiler/rustc_middle/src/query/mod.rs

@@ -54,14 +54,14 @@ rustc_queries! {
     /// This is because the `hir_crate` query gives you access to all other items.
     /// To avoid this fate, do not call `tcx.hir().krate()`; instead,
     /// prefer wrappers like `tcx.visit_all_items_in_krate()`.
-    query hir_crate(key: ()) -> Crate<'tcx> {
+    query hir_crate(key: ()) -> &'tcx Crate<'tcx> {
         arena_cache
         eval_always
         desc { "getting the crate HIR" }
     }
 
     /// All items in the crate.
-    query hir_crate_items(_: ()) -> rustc_middle::hir::ModuleItems {
+    query hir_crate_items(_: ()) -> &'tcx rustc_middle::hir::ModuleItems {
         arena_cache
         eval_always
         desc { "getting HIR crate items" }
@@ -71,7 +71,7 @@ rustc_queries! {
     ///
     /// This can be conveniently accessed by `tcx.hir().visit_item_likes_in_module`.
     /// Avoid calling this query directly.
-    query hir_module_items(key: LocalDefId) -> rustc_middle::hir::ModuleItems {
+    query hir_module_items(key: LocalDefId) -> &'tcx rustc_middle::hir::ModuleItems {
         arena_cache
         desc { |tcx| "getting HIR module items in `{}`", tcx.def_path_str(key.to_def_id()) }
         cache_on_disk_if { true }
@@ -183,7 +183,7 @@ rustc_queries! {
         separate_provide_extern
     }
 
-    query unsizing_params_for_adt(key: DefId) -> rustc_index::bit_set::BitSet<u32>
+    query unsizing_params_for_adt(key: DefId) -> &'tcx rustc_index::bit_set::BitSet<u32>
     {
         arena_cache
         desc { |tcx|
@@ -218,7 +218,7 @@ rustc_queries! {
 
     /// Maps from the `DefId` of an item (trait/struct/enum/fn) to its
     /// associated generics.
-    query generics_of(key: DefId) -> ty::Generics {
+    query generics_of(key: DefId) -> &'tcx ty::Generics {
         desc { |tcx| "computing generics of `{}`", tcx.def_path_str(key) }
         arena_cache
         cache_on_disk_if { key.is_local() }
@@ -295,19 +295,19 @@ rustc_queries! {
     /// These are assembled from the following places:
     /// - `extern` blocks (depending on their `link` attributes)
     /// - the `libs` (`-l`) option
-    query native_libraries(_: CrateNum) -> Vec<NativeLib> {
+    query native_libraries(_: CrateNum) -> &'tcx Vec<NativeLib> {
         arena_cache
         desc { "looking up the native libraries of a linked crate" }
         separate_provide_extern
     }
 
-    query shallow_lint_levels_on(key: hir::OwnerId) -> rustc_middle::lint::ShallowLintLevelMap {
+    query shallow_lint_levels_on(key: hir::OwnerId) -> &'tcx rustc_middle::lint::ShallowLintLevelMap {
         eval_always // fetches `resolutions`
         arena_cache
         desc { |tcx| "looking up lint levels for `{}`", tcx.def_path_str(key.to_def_id()) }
     }
 
-    query lint_expectations(_: ()) -> Vec<(LintExpectationId, LintExpectation)> {
+    query lint_expectations(_: ()) -> &'tcx Vec<(LintExpectationId, LintExpectation)> {
         arena_cache
         desc { "computing `#[expect]`ed lints in this crate" }
     }
@@ -347,7 +347,7 @@ rustc_queries! {
     }
 
     /// Set of param indexes for type params that are in the type's representation
-    query params_in_repr(key: DefId) -> rustc_index::bit_set::BitSet<u32> {
+    query params_in_repr(key: DefId) -> &'tcx rustc_index::bit_set::BitSet<u32> {
         desc { "finding type parameters in the representation" }
         arena_cache
         no_hash
@@ -364,14 +364,14 @@ rustc_queries! {
     }
 
     /// Create a THIR tree for debugging.
-    query thir_tree(key: ty::WithOptConstParam<LocalDefId>) -> String {
+    query thir_tree(key: ty::WithOptConstParam<LocalDefId>) -> &'tcx String {
         no_hash
         arena_cache
         desc { |tcx| "constructing THIR tree for `{}`", tcx.def_path_str(key.did.to_def_id()) }
     }
 
     /// Create a list-like THIR representation for debugging.
-    query thir_flat(key: ty::WithOptConstParam<LocalDefId>) -> String {
+    query thir_flat(key: ty::WithOptConstParam<LocalDefId>) -> &'tcx String {
         no_hash
         arena_cache
         desc { |tcx| "constructing flat THIR representation for `{}`", tcx.def_path_str(key.did.to_def_id()) }
@@ -380,7 +380,7 @@ rustc_queries! {
     /// Set of all the `DefId`s in this crate that have MIR associated with
     /// them. This includes all the body owners, but also things like struct
     /// constructors.
-    query mir_keys(_: ()) -> rustc_data_structures::fx::FxIndexSet<LocalDefId> {
+    query mir_keys(_: ()) -> &'tcx rustc_data_structures::fx::FxIndexSet<LocalDefId> {
         arena_cache
         desc { "getting a list of all mir_keys" }
     }
@@ -478,7 +478,7 @@ rustc_queries! {
 
     query symbols_for_closure_captures(
         key: (LocalDefId, LocalDefId)
-    ) -> Vec<rustc_span::Symbol> {
+    ) -> &'tcx Vec<rustc_span::Symbol> {
         arena_cache
         desc {
             |tcx| "finding symbols for captures of closure `{}` in `{}`",
@@ -487,7 +487,7 @@ rustc_queries! {
         }
     }
 
-    query mir_generator_witnesses(key: DefId) -> mir::GeneratorLayout<'tcx> {
+    query mir_generator_witnesses(key: DefId) -> &'tcx mir::GeneratorLayout<'tcx> {
         arena_cache
         desc { |tcx| "generator witness types for `{}`", tcx.def_path_str(key) }
         cache_on_disk_if { key.is_local() }
@@ -508,14 +508,14 @@ rustc_queries! {
 
     /// Returns coverage summary info for a function, after executing the `InstrumentCoverage`
     /// MIR pass (assuming the -Cinstrument-coverage option is enabled).
-    query coverageinfo(key: ty::InstanceDef<'tcx>) -> mir::CoverageInfo {
+    query coverageinfo(key: ty::InstanceDef<'tcx>) -> &'tcx mir::CoverageInfo {
         desc { |tcx| "retrieving coverage info from MIR for `{}`", tcx.def_path_str(key.def_id()) }
         arena_cache
     }
 
     /// Returns the `CodeRegions` for a function that has instrumented coverage, in case the
     /// function was optimized out before codegen, and before being added to the Coverage Map.
-    query covered_code_regions(key: DefId) -> Vec<&'tcx mir::coverage::CodeRegion> {
+    query covered_code_regions(key: DefId) -> &'tcx Vec<&'tcx mir::coverage::CodeRegion> {
         desc {
             |tcx| "retrieving the covered `CodeRegion`s, if instrumented, for `{}`",
             tcx.def_path_str(key)
@@ -557,7 +557,7 @@ rustc_queries! {
         desc { "erasing regions from `{}`", ty }
     }
 
-    query wasm_import_module_map(_: CrateNum) -> FxHashMap<DefId, String> {
+    query wasm_import_module_map(_: CrateNum) -> &'tcx FxHashMap<DefId, String> {
         arena_cache
         desc { "getting wasm import module map" }
     }
@@ -632,7 +632,7 @@ rustc_queries! {
         desc { |tcx| "computing the bounds for type parameter `{}`", tcx.hir().ty_param_name(key.1) }
     }
 
-    query trait_def(key: DefId) -> ty::TraitDef {
+    query trait_def(key: DefId) -> &'tcx ty::TraitDef {
         desc { |tcx| "computing trait definition for `{}`", tcx.def_path_str(key) }
         arena_cache
         cache_on_disk_if { key.is_local() }
@@ -703,7 +703,7 @@ rustc_queries! {
     }
 
     /// Gets a map with the variance of every item; use `item_variance` instead.
-    query crate_variances(_: ()) -> ty::CrateVariancesMap<'tcx> {
+    query crate_variances(_: ()) -> &'tcx ty::CrateVariancesMap<'tcx> {
         arena_cache
         desc { "computing the variances for items in this crate" }
     }
@@ -716,7 +716,7 @@ rustc_queries! {
     }
 
     /// Maps from thee `DefId` of a type to its (inferred) outlives.
-    query inferred_outlives_crate(_: ()) -> ty::CratePredicatesMap<'tcx> {
+    query inferred_outlives_crate(_: ()) -> &'tcx ty::CratePredicatesMap<'tcx> {
         arena_cache
         desc { "computing the inferred outlives predicates for items in this crate" }
     }
@@ -729,7 +729,7 @@ rustc_queries! {
     }
 
     /// Maps from a trait item to the trait item "descriptor".
-    query associated_item(key: DefId) -> ty::AssocItem {
+    query associated_item(key: DefId) -> &'tcx ty::AssocItem {
         desc { |tcx| "computing associated item data for `{}`", tcx.def_path_str(key) }
         arena_cache
         cache_on_disk_if { key.is_local() }
@@ -737,7 +737,7 @@ rustc_queries! {
     }
 
     /// Collects the associated items defined on a trait or impl.
-    query associated_items(key: DefId) -> ty::AssocItems<'tcx> {
+    query associated_items(key: DefId) -> &'tcx ty::AssocItems<'tcx> {
         arena_cache
         desc { |tcx| "collecting associated items of `{}`", tcx.def_path_str(key) }
     }
@@ -763,7 +763,7 @@ rustc_queries! {
     ///
     /// The map returned for `tcx.impl_item_implementor_ids(impl_id)` would be
     ///`{ trait_f: impl_f, trait_g: impl_g }`
-    query impl_item_implementor_ids(impl_id: DefId) -> FxHashMap<DefId, DefId> {
+    query impl_item_implementor_ids(impl_id: DefId) -> &'tcx FxHashMap<DefId, DefId> {
         arena_cache
         desc { |tcx| "comparing impl items against trait for `{}`", tcx.def_path_str(impl_id) }
     }
@@ -884,7 +884,7 @@ rustc_queries! {
     ///
     /// The second return value maps from ADTs to ignored derived traits (e.g. Debug and Clone) and
     /// their respective impl (i.e., part of the derive macro)
-    query live_symbols_and_ignored_derived_traits(_: ()) -> (
+    query live_symbols_and_ignored_derived_traits(_: ()) -> &'tcx (
         FxHashSet<LocalDefId>,
         FxHashMap<LocalDefId, Vec<(DefId, DefId)>>
     ) {
@@ -964,7 +964,7 @@ rustc_queries! {
 
     /// Gets a complete map from all types to their inherent impls.
     /// Not meant to be used directly outside of coherence.
-    query crate_inherent_impls(k: ()) -> CrateInherentImpls {
+    query crate_inherent_impls(k: ()) -> &'tcx CrateInherentImpls {
         arena_cache
         desc { "finding all inherent impls defined in crate" }
     }
@@ -1099,7 +1099,7 @@ rustc_queries! {
         desc { "checking for private elements in public interfaces" }
     }
 
-    query reachable_set(_: ()) -> FxHashSet<LocalDefId> {
+    query reachable_set(_: ()) -> &'tcx FxHashSet<LocalDefId> {
         arena_cache
         desc { "reachability" }
     }
@@ -1111,7 +1111,7 @@ rustc_queries! {
     }
 
     /// Generates a MIR body for the shim.
-    query mir_shims(key: ty::InstanceDef<'tcx>) -> mir::Body<'tcx> {
+    query mir_shims(key: ty::InstanceDef<'tcx>) -> &'tcx mir::Body<'tcx> {
         arena_cache
         desc { |tcx| "generating MIR shim for `{}`", tcx.def_path_str(key.def_id()) }
     }
@@ -1191,7 +1191,7 @@ rustc_queries! {
         separate_provide_extern
     }
 
-    query codegen_fn_attrs(def_id: DefId) -> CodegenFnAttrs {
+    query codegen_fn_attrs(def_id: DefId) -> &'tcx CodegenFnAttrs {
         desc { |tcx| "computing codegen attributes of `{}`", tcx.def_path_str(def_id) }
         arena_cache
         cache_on_disk_if { def_id.is_local() }
@@ -1209,7 +1209,7 @@ rustc_queries! {
     }
     /// Gets the rendered value of the specified constant or associated constant.
     /// Used by rustdoc.
-    query rendered_const(def_id: DefId) -> String {
+    query rendered_const(def_id: DefId) -> &'tcx String {
         arena_cache
         desc { |tcx| "rendering constant initializer of `{}`", tcx.def_path_str(def_id) }
         cache_on_disk_if { def_id.is_local() }
@@ -1268,12 +1268,12 @@ rustc_queries! {
     }
 
     /// Given a trait `trait_id`, return all known `impl` blocks.
-    query trait_impls_of(trait_id: DefId) -> ty::trait_def::TraitImpls {
+    query trait_impls_of(trait_id: DefId) -> &'tcx ty::trait_def::TraitImpls {
         arena_cache
         desc { |tcx| "finding trait impls of `{}`", tcx.def_path_str(trait_id) }
     }
 
-    query specialization_graph_of(trait_id: DefId) -> specialization_graph::Graph {
+    query specialization_graph_of(trait_id: DefId) -> &'tcx specialization_graph::Graph {
         arena_cache
         desc { |tcx| "building specialization graph of trait `{}`", tcx.def_path_str(trait_id) }
         cache_on_disk_if { true }
@@ -1403,7 +1403,7 @@ rustc_queries! {
         separate_provide_extern
     }
 
-    query dependency_formats(_: ()) -> Lrc<crate::middle::dependency_format::Dependencies> {
+    query dependency_formats(_: ()) -> &'tcx Lrc<crate::middle::dependency_format::Dependencies> {
         arena_cache
         desc { "getting the linkage format of all dependencies" }
     }
@@ -1503,7 +1503,7 @@ rustc_queries! {
     // Does not include external symbols that don't have a corresponding DefId,
     // like the compiler-generated `main` function and so on.
     query reachable_non_generics(_: CrateNum)
-        -> DefIdMap<SymbolExportInfo> {
+        -> &'tcx DefIdMap<SymbolExportInfo> {
         arena_cache
         desc { "looking up the exported symbols of a crate" }
         separate_provide_extern
@@ -1526,7 +1526,7 @@ rustc_queries! {
     /// added or removed in any upstream crate. Instead use the narrower
     /// `upstream_monomorphizations_for`, `upstream_drop_glue_for`, or, even
     /// better, `Instance::upstream_monomorphization()`.
-    query upstream_monomorphizations(_: ()) -> DefIdMap<FxHashMap<SubstsRef<'tcx>, CrateNum>> {
+    query upstream_monomorphizations(_: ()) -> &'tcx DefIdMap<FxHashMap<SubstsRef<'tcx>, CrateNum>> {
         arena_cache
         desc { "collecting available upstream monomorphizations" }
     }
@@ -1568,7 +1568,7 @@ rustc_queries! {
     }
 
     /// Returns a list of all `extern` blocks of a crate.
-    query foreign_modules(_: CrateNum) -> FxHashMap<DefId, ForeignModule> {
+    query foreign_modules(_: CrateNum) -> &'tcx FxHashMap<DefId, ForeignModule> {
         arena_cache
         desc { "looking up the foreign modules of a linked crate" }
         separate_provide_extern
@@ -1602,7 +1602,7 @@ rustc_queries! {
 
     /// Gets the extra data to put in each output filename for a crate.
     /// For example, compiling the `foo` crate with `extra-filename=-a` creates a `libfoo-b.rlib` file.
-    query extra_filename(_: CrateNum) -> String {
+    query extra_filename(_: CrateNum) -> &'tcx String {
         arena_cache
         eval_always
         desc { "looking up the extra filename for a crate" }
@@ -1610,7 +1610,7 @@ rustc_queries! {
     }
 
     /// Gets the paths where the crate came from in the file system.
-    query crate_extern_paths(_: CrateNum) -> Vec<PathBuf> {
+    query crate_extern_paths(_: CrateNum) -> &'tcx Vec<PathBuf> {
         arena_cache
         eval_always
         desc { "looking up the paths for extern crates" }
@@ -1641,7 +1641,7 @@ rustc_queries! {
     /// Does lifetime resolution on items. Importantly, we can't resolve
     /// lifetimes directly on things like trait methods, because of trait params.
     /// See `rustc_resolve::late::lifetimes for details.
-    query resolve_lifetimes(_: hir::OwnerId) -> ResolveLifetimes {
+    query resolve_lifetimes(_: hir::OwnerId) -> &'tcx ResolveLifetimes {
         arena_cache
         desc { "resolving lifetimes" }
     }
@@ -1712,7 +1712,7 @@ rustc_queries! {
         desc { |tcx| "computing crate imported by `{}`", tcx.def_path_str(def_id.to_def_id()) }
     }
 
-    query lib_features(_: ()) -> LibFeatures {
+    query lib_features(_: ()) -> &'tcx LibFeatures {
         arena_cache
         desc { "calculating the lib features map" }
     }
@@ -1720,7 +1720,7 @@ rustc_queries! {
         desc { "calculating the lib features defined in a crate" }
         separate_provide_extern
     }
-    query stability_implications(_: CrateNum) -> FxHashMap<Symbol, Symbol> {
+    query stability_implications(_: CrateNum) -> &'tcx FxHashMap<Symbol, Symbol> {
         arena_cache
         desc { "calculating the implications between `#[unstable]` features defined in a crate" }
         separate_provide_extern
@@ -1731,14 +1731,14 @@ rustc_queries! {
         separate_provide_extern
     }
     /// Returns the lang items defined in another crate by loading it from metadata.
-    query get_lang_items(_: ()) -> LanguageItems {
+    query get_lang_items(_: ()) -> &'tcx LanguageItems {
         arena_cache
         eval_always
         desc { "calculating the lang items map" }
     }
 
     /// Returns all diagnostic items defined in all crates.
-    query all_diagnostic_items(_: ()) -> rustc_hir::diagnostic_items::DiagnosticItems {
+    query all_diagnostic_items(_: ()) -> &'tcx rustc_hir::diagnostic_items::DiagnosticItems {
         arena_cache
         eval_always
         desc { "calculating the diagnostic items map" }
@@ -1751,7 +1751,7 @@ rustc_queries! {
     }
 
     /// Returns the diagnostic items defined in a crate.
-    query diagnostic_items(_: CrateNum) -> rustc_hir::diagnostic_items::DiagnosticItems {
+    query diagnostic_items(_: CrateNum) -> &'tcx rustc_hir::diagnostic_items::DiagnosticItems {
         arena_cache
         desc { "calculating the diagnostic items map in a crate" }
         separate_provide_extern
@@ -1761,11 +1761,11 @@ rustc_queries! {
         desc { "calculating the missing lang items in a crate" }
         separate_provide_extern
     }
-    query visible_parent_map(_: ()) -> DefIdMap<DefId> {
+    query visible_parent_map(_: ()) -> &'tcx DefIdMap<DefId> {
         arena_cache
         desc { "calculating the visible parent map" }
     }
-    query trimmed_def_paths(_: ()) -> FxHashMap<DefId, Symbol> {
+    query trimmed_def_paths(_: ()) -> &'tcx FxHashMap<DefId, Symbol> {
         arena_cache
         desc { "calculating trimmed def paths" }
     }
@@ -1774,14 +1774,14 @@ rustc_queries! {
         desc { "seeing if we're missing an `extern crate` item for this crate" }
         separate_provide_extern
     }
-    query used_crate_source(_: CrateNum) -> Lrc<CrateSource> {
+    query used_crate_source(_: CrateNum) -> &'tcx Lrc<CrateSource> {
         arena_cache
         eval_always
         desc { "looking at the source for a crate" }
         separate_provide_extern
     }
     /// Returns the debugger visualizers defined for this crate.
-    query debugger_visualizers(_: CrateNum) -> Vec<rustc_span::DebuggerVisualizerFile> {
+    query debugger_visualizers(_: CrateNum) -> &'tcx Vec<rustc_span::DebuggerVisualizerFile> {
         arena_cache
         desc { "looking up the debugger visualizers for this crate" }
         separate_provide_extern
@@ -1819,7 +1819,7 @@ rustc_queries! {
         desc { |tcx| "finding names imported by glob use for `{}`", tcx.def_path_str(def_id.to_def_id()) }
     }
 
-    query stability_index(_: ()) -> stability::Index {
+    query stability_index(_: ()) -> &'tcx stability::Index {
         arena_cache
         eval_always
         desc { "calculating the stability index for the local crate" }
@@ -1883,7 +1883,7 @@ rustc_queries! {
     ///
     /// This query returns an `&Arc` because codegen backends need the value even after the `TyCtxt`
     /// has been destroyed.
-    query output_filenames(_: ()) -> Arc<OutputFilenames> {
+    query output_filenames(_: ()) -> &'tcx Arc<OutputFilenames> {
         feedable
         desc { "getting output filenames" }
         arena_cache
@@ -2056,7 +2056,7 @@ rustc_queries! {
         remap_env_constness
     }
 
-    query supported_target_features(_: CrateNum) -> FxHashMap<String, Option<Symbol>> {
+    query supported_target_features(_: CrateNum) -> &'tcx FxHashMap<String, Option<Symbol>> {
         arena_cache
         eval_always
         desc { "looking up supported target features" }
@@ -2115,23 +2115,24 @@ rustc_queries! {
     /// span) for an *existing* error. Therefore, it is best-effort, and may never handle
     /// all of the cases that the normal `ty::Ty`-based wfcheck does. This is fine,
     /// because the `ty::Ty`-based wfcheck is always run.
-    query diagnostic_hir_wf_check(key: (ty::Predicate<'tcx>, traits::WellFormedLoc)) -> Option<traits::ObligationCause<'tcx>> {
+    query diagnostic_hir_wf_check(
+        key: (ty::Predicate<'tcx>, traits::WellFormedLoc)
+    ) -> &'tcx Option<traits::ObligationCause<'tcx>> {
         arena_cache
         eval_always
         no_hash
         desc { "performing HIR wf-checking for predicate `{:?}` at item `{:?}`", key.0, key.1 }
     }
 
-
     /// The list of backend features computed from CLI flags (`-Ctarget-cpu`, `-Ctarget-feature`,
     /// `--target` and similar).
-    query global_backend_features(_: ()) -> Vec<String> {
+    query global_backend_features(_: ()) -> &'tcx Vec<String> {
         arena_cache
         eval_always
         desc { "computing the backend features for CLI flags" }
     }
 
-    query generator_diagnostic_data(key: DefId) -> Option<GeneratorDiagnosticData<'tcx>> {
+    query generator_diagnostic_data(key: DefId) -> &'tcx Option<GeneratorDiagnosticData<'tcx>> {
         arena_cache
         desc { |tcx| "looking up generator diagnostic data of `{}`", tcx.def_path_str(key) }
         separate_provide_extern

compiler/rustc_middle/src/ty/query.rs

@@ -112,15 +112,15 @@ macro_rules! query_helper_param_ty {
     ($K:ty) => { $K };
 }
 
-macro_rules! query_storage {
+macro_rules! query_if_arena {
-    ([][$K:ty, $V:ty]) => {
+    ([] $arena:ty, $no_arena:ty) => {
-        <<$K as Key>::CacheSelector as CacheSelector<'tcx, $V>>::Cache
+        $no_arena
     };
-    ([(arena_cache) $($rest:tt)*][$K:ty, $V:ty]) => {
+    ([(arena_cache) $($rest:tt)*] $arena:ty, $no_arena:ty) => {
-        <<$K as Key>::CacheSelector as CacheSelector<'tcx, $V>>::ArenaCache
+        $arena
     };
-    ([$other:tt $($modifiers:tt)*][$($args:tt)*]) => {
+    ([$other:tt $($modifiers:tt)*]$($args:tt)*) => {
-        query_storage!([$($modifiers)*][$($args)*])
+        query_if_arena!([$($modifiers)*]$($args)*)
     };
 }
 
@@ -184,23 +184,30 @@ macro_rules! define_callbacks {
 
             $(pub type $name<'tcx> = $($K)*;)*
         }
-        #[allow(nonstandard_style, unused_lifetimes)]
+        #[allow(nonstandard_style, unused_lifetimes, unused_parens)]
         pub mod query_values {
             use super::*;
 
-            $(pub type $name<'tcx> = $V;)*
+            $(pub type $name<'tcx> = query_if_arena!([$($modifiers)*] <$V as Deref>::Target, $V);)*
         }
-        #[allow(nonstandard_style, unused_lifetimes)]
+        #[allow(nonstandard_style, unused_lifetimes, unused_parens)]
         pub mod query_storage {
             use super::*;
 
-            $(pub type $name<'tcx> = query_storage!([$($modifiers)*][$($K)*, $V]);)*
+            $(
+                pub type $name<'tcx> = query_if_arena!([$($modifiers)*]
+                    <<$($K)* as Key>::CacheSelector
+                        as CacheSelector<'tcx, <$V as Deref>::Target>>::ArenaCache,
+                    <<$($K)* as Key>::CacheSelector as CacheSelector<'tcx, $V>>::Cache
+                );
+            )*
         }
+
         #[allow(nonstandard_style, unused_lifetimes)]
         pub mod query_stored {
             use super::*;
 
-            $(pub type $name<'tcx> = <query_storage::$name<'tcx> as QueryStorage>::Stored;)*
+            $(pub type $name<'tcx> = $V;)*
         }
 
         #[derive(Default)]
@@ -226,7 +233,7 @@ macro_rules! define_callbacks {
             $($(#[$attr])*
             #[inline(always)]
             #[must_use]
-            pub fn $name(self, key: query_helper_param_ty!($($K)*)) -> query_stored::$name<'tcx>
+            pub fn $name(self, key: query_helper_param_ty!($($K)*)) -> $V
             {
                 self.at(DUMMY_SP).$name(key)
             })*
@@ -235,7 +242,7 @@ macro_rules! define_callbacks {
         impl<'tcx> TyCtxtAt<'tcx> {
             $($(#[$attr])*
             #[inline(always)]
-            pub fn $name(self, key: query_helper_param_ty!($($K)*)) -> query_stored::$name<'tcx>
+            pub fn $name(self, key: query_helper_param_ty!($($K)*)) -> $V
             {
                 let key = key.into_query_param();
                 opt_remap_env_constness!([$($modifiers)*][key]);
@@ -306,7 +313,7 @@ macro_rules! define_callbacks {
                 span: Span,
                 key: query_keys::$name<'tcx>,
                 mode: QueryMode,
-            ) -> Option<query_stored::$name<'tcx>>;)*
+            ) -> Option<$V>;)*
         }
     };
 }
@@ -328,7 +335,7 @@ macro_rules! define_feedable {
         $(impl<'tcx, K: IntoQueryParam<$($K)*> + Copy> TyCtxtFeed<'tcx, K> {
             $(#[$attr])*
             #[inline(always)]
-            pub fn $name(self, value: $V) -> query_stored::$name<'tcx> {
+            pub fn $name(self, value: query_values::$name<'tcx>) -> $V {
                 let key = self.key().into_query_param();
                 opt_remap_env_constness!([$($modifiers)*][key]);
 

compiler/rustc_mir_dataflow/src/drop_flag_effects.rs

@@ -1,5 +1,5 @@
 use crate::elaborate_drops::DropFlagState;
-use rustc_middle::mir::{self, Body, Location};
+use rustc_middle::mir::{self, Body, Location, Terminator, TerminatorKind};
 use rustc_middle::ty::{self, TyCtxt};
 use rustc_target::abi::VariantIdx;
 
@@ -194,6 +194,17 @@ pub fn drop_flag_effects_for_location<'tcx, F>(
         on_all_children_bits(tcx, body, move_data, path, |mpi| callback(mpi, DropFlagState::Absent))
     }
 
+    // Drop does not count as a move but we should still consider the variable uninitialized.
+    if let Some(Terminator { kind: TerminatorKind::Drop { place, .. }, .. }) =
+        body.stmt_at(loc).right()
+    {
+        if let LookupResult::Exact(mpi) = move_data.rev_lookup.find(place.as_ref()) {
+            on_all_children_bits(tcx, body, move_data, mpi, |mpi| {
+                callback(mpi, DropFlagState::Absent)
+            })
+        }
+    }
+
     debug!("drop_flag_effects: assignment for location({:?})", loc);
 
     for_location_inits(tcx, body, move_data, loc, |mpi| callback(mpi, DropFlagState::Present));

compiler/rustc_mir_dataflow/src/move_paths/builder.rs

@@ -376,7 +376,8 @@ impl<'b, 'a, 'tcx> Gatherer<'b, 'a, 'tcx> {
             | TerminatorKind::Resume
             | TerminatorKind::Abort
             | TerminatorKind::GeneratorDrop
-            | TerminatorKind::Unreachable => {}
+            | TerminatorKind::Unreachable
+            | TerminatorKind::Drop { .. } => {}
 
             TerminatorKind::Assert { ref cond, .. } => {
                 self.gather_operand(cond);
@@ -391,10 +392,6 @@ impl<'b, 'a, 'tcx> Gatherer<'b, 'a, 'tcx> {
                 self.create_move_path(place);
                 self.gather_init(place.as_ref(), InitKind::Deep);
             }
-
-            TerminatorKind::Drop { place, target: _, unwind: _ } => {
-                self.gather_move(place);
-            }
             TerminatorKind::DropAndReplace { place, ref value, .. } => {
                 self.create_move_path(place);
                 self.gather_operand(value);

compiler/rustc_mir_dataflow/src/value_analysis.rs

@@ -223,13 +223,13 @@ pub trait ValueAnalysis<'tcx> {
         self.super_terminator(terminator, state)
     }
 
-    fn super_terminator(&self, terminator: &Terminator<'tcx>, _state: &mut State<Self::Value>) {
+    fn super_terminator(&self, terminator: &Terminator<'tcx>, state: &mut State<Self::Value>) {
         match &terminator.kind {
             TerminatorKind::Call { .. } | TerminatorKind::InlineAsm { .. } => {
                 // Effect is applied by `handle_call_return`.
             }
-            TerminatorKind::Drop { .. } => {
+            TerminatorKind::Drop { place, .. } => {
-                // We don't track dropped places.
+                state.flood_with(place.as_ref(), self.map(), Self::Value::bottom());
             }
             TerminatorKind::DropAndReplace { .. } | TerminatorKind::Yield { .. } => {
                 // They would have an effect, but are not allowed in this phase.

compiler/rustc_mir_transform/src/elaborate_drops.rs

@@ -18,6 +18,35 @@ use rustc_span::Span;
 use rustc_target::abi::VariantIdx;
 use std::fmt;
 
+/// During MIR building, Drop and DropAndReplace terminators are inserted in every place where a drop may occur.
+/// However, in this phase, the presence of these terminators does not guarantee that a destructor will run,
+/// as the target of the drop may be uninitialized.
+/// In general, the compiler cannot determine at compile time whether a destructor will run or not.
+///
+/// At a high level, this pass refines Drop and DropAndReplace to only run the destructor if the
+/// target is initialized. The way this is achievied is by inserting drop flags for every variable
+/// that may be dropped, and then using those flags to determine whether a destructor should run.
+/// This pass also removes DropAndReplace, replacing it with a Drop paired with an assign statement.
+/// Once this is complete, Drop terminators in the MIR correspond to a call to the "drop glue" or
+/// "drop shim" for the type of the dropped place.
+///
+/// This pass relies on dropped places having an associated move path, which is then used to determine
+/// the initialization status of the place and its descendants.
+/// It's worth noting that a MIR containing a Drop without an associated move path is probably ill formed,
+/// as it would allow running a destructor on a place behind a reference:
+///
+/// ```text
+// fn drop_term<T>(t: &mut T) {
+//     mir!(
+//         {
+//             Drop(*t, exit)
+//         }
+//         exit = {
+//             Return()
+//         }
+//     )
+// }
+/// ```
 pub struct ElaborateDrops;
 
 impl<'tcx> MirPass<'tcx> for ElaborateDrops {

compiler/rustc_trait_selection/src/solve/fulfill.rs

@@ -74,7 +74,7 @@ impl<'tcx> TraitEngine<'tcx> for FulfillmentCtxt<'tcx> {
                                     )
                                 }
                                 ty::PredicateKind::Subtype(pred) => {
-                                    let (a, b) = infcx.replace_bound_vars_with_placeholders(
+                                    let (a, b) = infcx.instantiate_binder_with_placeholders(
                                         goal.predicate.kind().rebind((pred.a, pred.b)),
                                     );
                                     let expected_found = ExpectedFound::new(true, a, b);
@@ -84,7 +84,7 @@ impl<'tcx> TraitEngine<'tcx> for FulfillmentCtxt<'tcx> {
                                     )
                                 }
                                 ty::PredicateKind::Coerce(pred) => {
-                                    let (a, b) = infcx.replace_bound_vars_with_placeholders(
+                                    let (a, b) = infcx.instantiate_binder_with_placeholders(
                                         goal.predicate.kind().rebind((pred.a, pred.b)),
                                     );
                                     let expected_found = ExpectedFound::new(false, a, b);
@@ -94,7 +94,7 @@ impl<'tcx> TraitEngine<'tcx> for FulfillmentCtxt<'tcx> {
                                     )
                                 }
                                 ty::PredicateKind::ConstEquate(a, b) => {
-                                    let (a, b) = infcx.replace_bound_vars_with_placeholders(
+                                    let (a, b) = infcx.instantiate_binder_with_placeholders(
                                         goal.predicate.kind().rebind((a, b)),
                                     );
                                     let expected_found = ExpectedFound::new(true, a, b);

compiler/rustc_trait_selection/src/solve/infcx_ext.rs

@@ -26,7 +26,7 @@ pub(super) trait InferCtxtExt<'tcx> {
         rhs: T,
     ) -> Result<Vec<Goal<'tcx, ty::Predicate<'tcx>>>, NoSolution>;
 
-    fn instantiate_bound_vars_with_infer<T: TypeFoldable<'tcx> + Copy>(
+    fn instantiate_binder_with_infer<T: TypeFoldable<'tcx> + Copy>(
         &self,
         value: ty::Binder<'tcx, T>,
     ) -> T;
@@ -65,11 +65,11 @@ impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
             })
     }
 
-    fn instantiate_bound_vars_with_infer<T: TypeFoldable<'tcx> + Copy>(
+    fn instantiate_binder_with_infer<T: TypeFoldable<'tcx> + Copy>(
         &self,
         value: ty::Binder<'tcx, T>,
     ) -> T {
-        self.replace_bound_vars_with_fresh_vars(
+        self.instantiate_binder_with_fresh_vars(
             DUMMY_SP,
             LateBoundRegionConversionTime::HigherRankedType,
             value,

compiler/rustc_trait_selection/src/solve/mod.rs

@@ -304,7 +304,7 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
                 }
             }
         } else {
-            let kind = self.infcx.replace_bound_vars_with_placeholders(kind);
+            let kind = self.infcx.instantiate_binder_with_placeholders(kind);
             let goal = goal.with(self.tcx(), ty::Binder::dummy(kind));
             let (_, certainty) = self.evaluate_goal(goal)?;
             self.make_canonical_response(certainty)

compiler/rustc_trait_selection/src/solve/project_goals.rs

@@ -323,7 +323,7 @@ impl<'tcx> assembly::GoalKind<'tcx> for ProjectionPredicate<'tcx> {
         {
             ecx.infcx.probe(|_| {
                 let assumption_projection_pred =
-                    ecx.infcx.instantiate_bound_vars_with_infer(poly_projection_pred);
+                    ecx.infcx.instantiate_binder_with_infer(poly_projection_pred);
                 let nested_goals = ecx.infcx.eq(
                     goal.param_env,
                     goal.predicate.projection_ty,

compiler/rustc_trait_selection/src/solve/trait_goals.rs

@@ -72,7 +72,7 @@ impl<'tcx> assembly::GoalKind<'tcx> for TraitPredicate<'tcx> {
             // FIXME: Constness and polarity
             ecx.infcx.probe(|_| {
                 let assumption_trait_pred =
-                    ecx.infcx.instantiate_bound_vars_with_infer(poly_trait_pred);
+                    ecx.infcx.instantiate_binder_with_infer(poly_trait_pred);
                 let nested_goals = ecx.infcx.eq(
                     goal.param_env,
                     goal.predicate.trait_ref,

compiler/rustc_trait_selection/src/solve/trait_goals/structural_traits.rs

@@ -54,7 +54,7 @@ pub(super) fn instantiate_constituent_tys_for_auto_trait<'tcx>(
         }
 
         ty::GeneratorWitness(types) => {
-            Ok(infcx.replace_bound_vars_with_placeholders(types).to_vec())
+            Ok(infcx.instantiate_binder_with_placeholders(types).to_vec())
         }
 
         ty::GeneratorWitnessMIR(..) => todo!(),
@@ -174,7 +174,7 @@ pub(super) fn instantiate_constituent_tys_for_copy_clone_trait<'tcx>(
         }
 
         ty::GeneratorWitness(types) => {
-            Ok(infcx.replace_bound_vars_with_placeholders(types).to_vec())
+            Ok(infcx.instantiate_binder_with_placeholders(types).to_vec())
         }
 
         ty::GeneratorWitnessMIR(..) => todo!(),

compiler/rustc_trait_selection/src/traits/error_reporting/ambiguity.rs

@@ -22,7 +22,7 @@ pub fn recompute_applicable_impls<'tcx>(
     let impl_may_apply = |impl_def_id| {
         let ocx = ObligationCtxt::new_in_snapshot(infcx);
         let placeholder_obligation =
-            infcx.replace_bound_vars_with_placeholders(obligation.predicate);
+            infcx.instantiate_binder_with_placeholders(obligation.predicate);
         let obligation_trait_ref =
             ocx.normalize(&ObligationCause::dummy(), param_env, placeholder_obligation.trait_ref);
 
@@ -47,11 +47,11 @@ pub fn recompute_applicable_impls<'tcx>(
     let param_env_candidate_may_apply = |poly_trait_predicate: ty::PolyTraitPredicate<'tcx>| {
         let ocx = ObligationCtxt::new_in_snapshot(infcx);
         let placeholder_obligation =
-            infcx.replace_bound_vars_with_placeholders(obligation.predicate);
+            infcx.instantiate_binder_with_placeholders(obligation.predicate);
         let obligation_trait_ref =
             ocx.normalize(&ObligationCause::dummy(), param_env, placeholder_obligation.trait_ref);
 
-        let param_env_predicate = infcx.replace_bound_vars_with_fresh_vars(
+        let param_env_predicate = infcx.instantiate_binder_with_fresh_vars(
             DUMMY_SP,
             LateBoundRegionConversionTime::HigherRankedType,
             poly_trait_predicate,

compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs

@@ -1716,7 +1716,7 @@ impl<'tcx> InferCtxtPrivExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             let (values, err) = if let ty::PredicateKind::Clause(ty::Clause::Projection(data)) =
                 bound_predicate.skip_binder()
             {
-                let data = self.replace_bound_vars_with_fresh_vars(
+                let data = self.instantiate_binder_with_fresh_vars(
                     obligation.cause.span,
                     infer::LateBoundRegionConversionTime::HigherRankedType,
                     bound_predicate.rebind(data),

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -898,7 +898,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             return false;
         }
 
-        let self_ty = self.replace_bound_vars_with_fresh_vars(
+        let self_ty = self.instantiate_binder_with_fresh_vars(
             DUMMY_SP,
             LateBoundRegionConversionTime::FnCall,
             trait_pred.self_ty(),
@@ -1191,7 +1191,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             }
         }) else { return None; };
 
-        let output = self.replace_bound_vars_with_fresh_vars(
+        let output = self.instantiate_binder_with_fresh_vars(
             DUMMY_SP,
             LateBoundRegionConversionTime::FnCall,
             output,
@@ -1200,7 +1200,7 @@ impl<'tcx> TypeErrCtxtExt<'tcx> for TypeErrCtxt<'_, 'tcx> {
             .skip_binder()
             .iter()
             .map(|ty| {
-                self.replace_bound_vars_with_fresh_vars(
+                self.instantiate_binder_with_fresh_vars(
                     DUMMY_SP,
                     LateBoundRegionConversionTime::FnCall,
                     inputs.rebind(*ty),
@@ -3806,13 +3806,13 @@ fn hint_missing_borrow<'tcx>(
     err: &mut Diagnostic,
 ) {
     let found_args = match found.kind() {
-        ty::FnPtr(f) => infcx.replace_bound_vars_with_placeholders(*f).inputs().iter(),
+        ty::FnPtr(f) => infcx.instantiate_binder_with_placeholders(*f).inputs().iter(),
         kind => {
             span_bug!(span, "found was converted to a FnPtr above but is now {:?}", kind)
         }
     };
     let expected_args = match expected.kind() {
-        ty::FnPtr(f) => infcx.replace_bound_vars_with_placeholders(*f).inputs().iter(),
+        ty::FnPtr(f) => infcx.instantiate_binder_with_placeholders(*f).inputs().iter(),
         kind => {
             span_bug!(span, "expected was converted to a FnPtr above but is now {:?}", kind)
         }

compiler/rustc_trait_selection/src/traits/fulfill.rs

@@ -321,7 +321,7 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                 | ty::PredicateKind::ConstEvaluatable(..)
                 | ty::PredicateKind::ConstEquate(..) => {
                     let pred =
-                        ty::Binder::dummy(infcx.replace_bound_vars_with_placeholders(binder));
+                        ty::Binder::dummy(infcx.instantiate_binder_with_placeholders(binder));
                     ProcessResult::Changed(mk_pending(vec![obligation.with(infcx.tcx, pred)]))
                 }
                 ty::PredicateKind::Ambiguous => ProcessResult::Unchanged,

compiler/rustc_trait_selection/src/traits/project.rs

@@ -215,7 +215,7 @@ pub(super) fn poly_project_and_unify_type<'cx, 'tcx>(
     let r = infcx.commit_if_ok(|_snapshot| {
         let old_universe = infcx.universe();
         let placeholder_predicate =
-            infcx.replace_bound_vars_with_placeholders(obligation.predicate);
+            infcx.instantiate_binder_with_placeholders(obligation.predicate);
         let new_universe = infcx.universe();
 
         let placeholder_obligation = obligation.with(infcx.tcx, placeholder_predicate);
@@ -2046,7 +2046,7 @@ fn confirm_param_env_candidate<'cx, 'tcx>(
     let cause = &obligation.cause;
     let param_env = obligation.param_env;
 
-    let cache_entry = infcx.replace_bound_vars_with_fresh_vars(
+    let cache_entry = infcx.instantiate_binder_with_fresh_vars(
         cause.span,
         LateBoundRegionConversionTime::HigherRankedType,
         poly_cache_entry,

compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs

@@ -488,7 +488,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
             let poly_trait_predicate = self.infcx.resolve_vars_if_possible(obligation.predicate);
             let placeholder_trait_predicate =
-                self.infcx.replace_bound_vars_with_placeholders(poly_trait_predicate);
+                self.infcx.instantiate_binder_with_placeholders(poly_trait_predicate);
 
             // Count only those upcast versions that match the trait-ref
             // we are looking for. Specifically, do not only check for the

compiler/rustc_trait_selection/src/traits/select/confirmation.rs

@@ -151,7 +151,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
         let trait_predicate = self.infcx.shallow_resolve(obligation.predicate);
         let placeholder_trait_predicate =
-            self.infcx.replace_bound_vars_with_placeholders(trait_predicate).trait_ref;
+            self.infcx.instantiate_binder_with_placeholders(trait_predicate).trait_ref;
         let placeholder_self_ty = placeholder_trait_predicate.self_ty();
         let placeholder_trait_predicate = ty::Binder::dummy(placeholder_trait_predicate);
         let (def_id, substs) = match *placeholder_self_ty.kind() {
@@ -336,7 +336,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             let cause = obligation.derived_cause(BuiltinDerivedObligation);
 
             let poly_trait_ref = obligation.predicate.to_poly_trait_ref();
-            let trait_ref = self.infcx.replace_bound_vars_with_placeholders(poly_trait_ref);
+            let trait_ref = self.infcx.instantiate_binder_with_placeholders(poly_trait_ref);
             let trait_obligations: Vec<PredicateObligation<'_>> = self.impl_or_trait_obligations(
                 &cause,
                 obligation.recursion_depth + 1,
@@ -427,7 +427,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         let tcx = self.tcx();
         debug!(?obligation, ?index, "confirm_object_candidate");
 
-        let trait_predicate = self.infcx.replace_bound_vars_with_placeholders(obligation.predicate);
+        let trait_predicate = self.infcx.instantiate_binder_with_placeholders(obligation.predicate);
         let self_ty = self.infcx.shallow_resolve(trait_predicate.self_ty());
         let obligation_trait_ref = ty::Binder::dummy(trait_predicate.trait_ref);
         let ty::Dynamic(data, ..) = *self_ty.kind() else {
@@ -437,7 +437,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         let object_trait_ref = data.principal().unwrap_or_else(|| {
             span_bug!(obligation.cause.span, "object candidate with no principal")
         });
-        let object_trait_ref = self.infcx.replace_bound_vars_with_fresh_vars(
+        let object_trait_ref = self.infcx.instantiate_binder_with_fresh_vars(
             obligation.cause.span,
             HigherRankedType,
             object_trait_ref,
@@ -629,7 +629,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         }
 
         // Confirm the `type Output: Sized;` bound that is present on `FnOnce`
-        let output_ty = self.infcx.replace_bound_vars_with_placeholders(sig.output());
+        let output_ty = self.infcx.instantiate_binder_with_placeholders(sig.output());
         let output_ty = normalize_with_depth_to(
             self,
             obligation.param_env,
@@ -652,7 +652,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         debug!(?obligation, "confirm_trait_alias_candidate");
 
         let alias_def_id = obligation.predicate.def_id();
-        let predicate = self.infcx.replace_bound_vars_with_placeholders(obligation.predicate);
+        let predicate = self.infcx.instantiate_binder_with_placeholders(obligation.predicate);
         let trait_ref = predicate.trait_ref;
         let trait_def_id = trait_ref.def_id;
         let substs = trait_ref.substs;

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -1618,7 +1618,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
     ) -> smallvec::SmallVec<[(usize, ty::BoundConstness); 2]> {
         let poly_trait_predicate = self.infcx.resolve_vars_if_possible(obligation.predicate);
         let placeholder_trait_predicate =
-            self.infcx.replace_bound_vars_with_placeholders(poly_trait_predicate);
+            self.infcx.instantiate_binder_with_placeholders(poly_trait_predicate);
         debug!(?placeholder_trait_predicate);
 
         let tcx = self.infcx.tcx;
@@ -1738,7 +1738,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         potentially_unnormalized_candidates: bool,
     ) -> ProjectionMatchesProjection {
         let mut nested_obligations = Vec::new();
-        let infer_predicate = self.infcx.replace_bound_vars_with_fresh_vars(
+        let infer_predicate = self.infcx.instantiate_binder_with_fresh_vars(
             obligation.cause.span,
             LateBoundRegionConversionTime::HigherRankedType,
             env_predicate,
@@ -2339,7 +2339,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
             .flat_map(|ty| {
                 let ty: ty::Binder<'tcx, Ty<'tcx>> = types.rebind(*ty); // <----/
 
-                let placeholder_ty = self.infcx.replace_bound_vars_with_placeholders(ty);
+                let placeholder_ty = self.infcx.instantiate_binder_with_placeholders(ty);
                 let Normalized { value: normalized_ty, mut obligations } =
                     ensure_sufficient_stack(|| {
                         project::normalize_with_depth(
@@ -2418,7 +2418,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         obligation: &TraitObligation<'tcx>,
     ) -> Result<Normalized<'tcx, SubstsRef<'tcx>>, ()> {
         let placeholder_obligation =
-            self.infcx.replace_bound_vars_with_placeholders(obligation.predicate);
+            self.infcx.instantiate_binder_with_placeholders(obligation.predicate);
         let placeholder_obligation_trait_ref = placeholder_obligation.trait_ref;
 
         let impl_substs = self.infcx.fresh_substs_for_item(obligation.cause.span, impl_def_id);

library/alloc/src/collections/btree/borrow.rs

@@ -41,6 +41,28 @@ impl<'a, T> DormantMutRef<'a, T> {
         // SAFETY: our own safety conditions imply this reference is again unique.
         unsafe { &mut *self.ptr.as_ptr() }
     }
+
+    /// Borrows a new mutable reference from the unique borrow initially captured.
+    ///
+    /// # Safety
+    ///
+    /// The reborrow must have ended, i.e., the reference returned by `new` and
+    /// all pointers and references derived from it, must not be used anymore.
+    pub unsafe fn reborrow(&mut self) -> &'a mut T {
+        // SAFETY: our own safety conditions imply this reference is again unique.
+        unsafe { &mut *self.ptr.as_ptr() }
+    }
+
+    /// Borrows a new shared reference from the unique borrow initially captured.
+    ///
+    /// # Safety
+    ///
+    /// The reborrow must have ended, i.e., the reference returned by `new` and
+    /// all pointers and references derived from it, must not be used anymore.
+    pub unsafe fn reborrow_shared(&self) -> &'a T {
+        // SAFETY: our own safety conditions imply this reference is again unique.
+        unsafe { &*self.ptr.as_ptr() }
+    }
 }
 
 #[cfg(test)]

library/alloc/src/collections/btree/map.rs

@@ -6,7 +6,7 @@ use core::hash::{Hash, Hasher};
 use core::iter::{FromIterator, FusedIterator};
 use core::marker::PhantomData;
 use core::mem::{self, ManuallyDrop};
-use core::ops::{Index, RangeBounds};
+use core::ops::{Bound, Index, RangeBounds};
 use core::ptr;
 
 use crate::alloc::{Allocator, Global};
@@ -15,7 +15,7 @@ use super::borrow::DormantMutRef;
 use super::dedup_sorted_iter::DedupSortedIter;
 use super::navigate::{LazyLeafRange, LeafRange};
 use super::node::{self, marker, ForceResult::*, Handle, NodeRef, Root};
-use super::search::SearchResult::*;
+use super::search::{SearchBound, SearchResult::*};
 use super::set_val::SetValZST;
 
 mod entry;
@@ -2422,6 +2422,732 @@ impl<K, V, A: Allocator + Clone> BTreeMap<K, V, A> {
     pub const fn is_empty(&self) -> bool {
         self.len() == 0
     }
+
+    /// Returns a [`Cursor`] pointing at the first element that is above the
+    /// given bound.
+    ///
+    /// If no such element exists then a cursor pointing at the "ghost"
+    /// non-element is returned.
+    ///
+    /// Passing [`Bound::Unbounded`] will return a cursor pointing at the first
+    /// element of the map.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// #![feature(btree_cursors)]
+    ///
+    /// use std::collections::BTreeMap;
+    /// use std::ops::Bound;
+    ///
+    /// let mut a = BTreeMap::new();
+    /// a.insert(1, "a");
+    /// a.insert(2, "b");
+    /// a.insert(3, "c");
+    /// a.insert(4, "c");
+    /// let cursor = a.lower_bound(Bound::Excluded(&2));
+    /// assert_eq!(cursor.key(), Some(&3));
+    /// ```
+    #[unstable(feature = "btree_cursors", issue = "107540")]
+    pub fn lower_bound<Q>(&self, bound: Bound<&Q>) -> Cursor<'_, K, V>
+    where
+        K: Borrow<Q> + Ord,
+        Q: Ord,
+    {
+        let root_node = match self.root.as_ref() {
+            None => return Cursor { current: None, root: None },
+            Some(root) => root.reborrow(),
+        };
+        let edge = root_node.lower_bound(SearchBound::from_range(bound));
+        Cursor { current: edge.next_kv().ok(), root: self.root.as_ref() }
+    }
+
+    /// Returns a [`CursorMut`] pointing at the first element that is above the
+    /// given bound.
+    ///
+    /// If no such element exists then a cursor pointing at the "ghost"
+    /// non-element is returned.
+    ///
+    /// Passing [`Bound::Unbounded`] will return a cursor pointing at the first
+    /// element of the map.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// #![feature(btree_cursors)]
+    ///
+    /// use std::collections::BTreeMap;
+    /// use std::ops::Bound;
+    ///
+    /// let mut a = BTreeMap::new();
+    /// a.insert(1, "a");
+    /// a.insert(2, "b");
+    /// a.insert(3, "c");
+    /// a.insert(4, "c");
+    /// let cursor = a.lower_bound_mut(Bound::Excluded(&2));
+    /// assert_eq!(cursor.key(), Some(&3));
+    /// ```
+    #[unstable(feature = "btree_cursors", issue = "107540")]
+    pub fn lower_bound_mut<Q>(&mut self, bound: Bound<&Q>) -> CursorMut<'_, K, V, A>
+    where
+        K: Borrow<Q> + Ord,
+        Q: Ord,
+    {
+        let (root, dormant_root) = DormantMutRef::new(&mut self.root);
+        let root_node = match root.as_mut() {
+            None => {
+                return CursorMut {
+                    current: None,
+                    root: dormant_root,
+                    length: &mut self.length,
+                    alloc: &mut *self.alloc,
+                };
+            }
+            Some(root) => root.borrow_mut(),
+        };
+        let edge = root_node.lower_bound(SearchBound::from_range(bound));
+        CursorMut {
+            current: edge.next_kv().ok(),
+            root: dormant_root,
+            length: &mut self.length,
+            alloc: &mut *self.alloc,
+        }
+    }
+
+    /// Returns a [`Cursor`] pointing at the last element that is below the
+    /// given bound.
+    ///
+    /// If no such element exists then a cursor pointing at the "ghost"
+    /// non-element is returned.
+    ///
+    /// Passing [`Bound::Unbounded`] will return a cursor pointing at the last
+    /// element of the map.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// #![feature(btree_cursors)]
+    ///
+    /// use std::collections::BTreeMap;
+    /// use std::ops::Bound;
+    ///
+    /// let mut a = BTreeMap::new();
+    /// a.insert(1, "a");
+    /// a.insert(2, "b");
+    /// a.insert(3, "c");
+    /// a.insert(4, "c");
+    /// let cursor = a.upper_bound(Bound::Excluded(&3));
+    /// assert_eq!(cursor.key(), Some(&2));
+    /// ```
+    #[unstable(feature = "btree_cursors", issue = "107540")]
+    pub fn upper_bound<Q>(&self, bound: Bound<&Q>) -> Cursor<'_, K, V>
+    where
+        K: Borrow<Q> + Ord,
+        Q: Ord,
+    {
+        let root_node = match self.root.as_ref() {
+            None => return Cursor { current: None, root: None },
+            Some(root) => root.reborrow(),
+        };
+        let edge = root_node.upper_bound(SearchBound::from_range(bound));
+        Cursor { current: edge.next_back_kv().ok(), root: self.root.as_ref() }
+    }
+
+    /// Returns a [`CursorMut`] pointing at the last element that is below the
+    /// given bound.
+    ///
+    /// If no such element exists then a cursor pointing at the "ghost"
+    /// non-element is returned.
+    ///
+    /// Passing [`Bound::Unbounded`] will return a cursor pointing at the last
+    /// element of the map.
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// #![feature(btree_cursors)]
+    ///
+    /// use std::collections::BTreeMap;
+    /// use std::ops::Bound;
+    ///
+    /// let mut a = BTreeMap::new();
+    /// a.insert(1, "a");
+    /// a.insert(2, "b");
+    /// a.insert(3, "c");
+    /// a.insert(4, "c");
+    /// let cursor = a.upper_bound_mut(Bound::Excluded(&3));
+    /// assert_eq!(cursor.key(), Some(&2));
+    /// ```
+    #[unstable(feature = "btree_cursors", issue = "107540")]
+    pub fn upper_bound_mut<Q>(&mut self, bound: Bound<&Q>) -> CursorMut<'_, K, V, A>
+    where
+        K: Borrow<Q> + Ord,
+        Q: Ord,
+    {
+        let (root, dormant_root) = DormantMutRef::new(&mut self.root);
+        let root_node = match root.as_mut() {
+            None => {
+                return CursorMut {
+                    current: None,
+                    root: dormant_root,
+                    length: &mut self.length,
+                    alloc: &mut *self.alloc,
+                };
+            }
+            Some(root) => root.borrow_mut(),
+        };
+        let edge = root_node.upper_bound(SearchBound::from_range(bound));
+        CursorMut {
+            current: edge.next_back_kv().ok(),
+            root: dormant_root,
+            length: &mut self.length,
+            alloc: &mut *self.alloc,
+        }
+    }
+}
+
+/// A cursor over a `BTreeMap`.
+///
+/// A `Cursor` is like an iterator, except that it can freely seek back-and-forth.
+///
+/// Cursors always point to an element in the tree, and index in a logically circular way.
+/// To accommodate this, there is a "ghost" non-element that yields `None` between the last and
+/// first elements of the tree.
+///
+/// A `Cursor` is created with the [`BTreeMap::lower_bound`] and [`BTreeMap::upper_bound`] methods.
+#[unstable(feature = "btree_cursors", issue = "107540")]
+pub struct Cursor<'a, K: 'a, V: 'a> {
+    current: Option<Handle<NodeRef<marker::Immut<'a>, K, V, marker::LeafOrInternal>, marker::KV>>,
+    root: Option<&'a node::Root<K, V>>,
+}
+
+#[unstable(feature = "btree_cursors", issue = "107540")]
+impl<K, V> Clone for Cursor<'_, K, V> {
+    fn clone(&self) -> Self {
+        let Cursor { current, root } = *self;
+        Cursor { current, root }
+    }
+}
+
+#[unstable(feature = "btree_cursors", issue = "107540")]
+impl<K: Debug, V: Debug> Debug for Cursor<'_, K, V> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_tuple("Cursor").field(&self.key_value()).finish()
+    }
+}
+
+/// A cursor over a `BTreeMap` with editing operations.
+///
+/// A `Cursor` is like an iterator, except that it can freely seek back-and-forth, and can
+/// safely mutate the tree during iteration. This is because the lifetime of its yielded
+/// references is tied to its own lifetime, instead of just the underlying tree. This means
+/// cursors cannot yield multiple elements at once.
+///
+/// Cursors always point to an element in the tree, and index in a logically circular way.
+/// To accommodate this, there is a "ghost" non-element that yields `None` between the last and
+/// first elements of the tree.
+///
+/// A `Cursor` is created with the [`BTreeMap::lower_bound_mut`] and [`BTreeMap::upper_bound_mut`]
+/// methods.
+#[unstable(feature = "btree_cursors", issue = "107540")]
+pub struct CursorMut<
+    'a,
+    K: 'a,
+    V: 'a,
+    #[unstable(feature = "allocator_api", issue = "32838")] A = Global,
+> {
+    current: Option<Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, marker::KV>>,
+    root: DormantMutRef<'a, Option<node::Root<K, V>>>,
+    length: &'a mut usize,
+    alloc: &'a mut A,
+}
+
+#[unstable(feature = "btree_cursors", issue = "107540")]
+impl<K: Debug, V: Debug, A> Debug for CursorMut<'_, K, V, A> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_tuple("CursorMut").field(&self.key_value()).finish()
+    }
+}
+
+impl<'a, K, V> Cursor<'a, K, V> {
+    /// Moves the cursor to the next element of the `BTreeMap`.
+    ///
+    /// If the cursor is pointing to the "ghost" non-element then this will move it to
+    /// the first element of the `BTreeMap`. If it is pointing to the last
+    /// element of the `BTreeMap` then this will move it to the "ghost" non-element.
+    #[unstable(feature = "btree_cursors", issue = "107540")]
+    pub fn move_next(&mut self) {
+        match self.current.take() {
+            None => {
+                self.current = self.root.and_then(|root| {
+                    root.reborrow().first_leaf_edge().forget_node_type().right_kv().ok()
+                });
+            }
+            Some(current) => {
+                self.current = current.next_leaf_edge().next_kv().ok();
+            }
+        }
+    }
+
+    /// Moves the cursor to the previous element of the `BTreeMap`.
+    ///
+    /// If the cursor is pointing to the "ghost" non-element then this will move it to
+    /// the last element of the `BTreeMap`. If it is pointing to the first
+    /// element of the `BTreeMap` then this will move it to the "ghost" non-element.
+    #[unstable(feature = "btree_cursors", issue = "107540")]
+    pub fn move_prev(&mut self) {
+        match self.current.take() {
+            None => {
+                self.current = self.root.and_then(|root| {
+                    root.reborrow().last_leaf_edge().forget_node_type().left_kv().ok()
+                });
+            }
+            Some(current) => {
+                self.current = current.next_back_leaf_edge().next_back_kv().ok();
+            }
+        }
+    }
+
+    /// Returns a reference to the key of the element that the cursor is
+    /// currently pointing to.
+    ///
+    /// This returns `None` if the cursor is currently pointing to the
+    /// "ghost" non-element.
+    #[unstable(feature = "btree_cursors", issue = "107540")]
+    pub fn key(&self) -> Option<&'a K> {
+        self.current.as_ref().map(|current| current.into_kv().0)
+    }
+
+    /// Returns a reference to the value of the element that the cursor is
+    /// currently pointing to.
+    ///
+    /// This returns `None` if the cursor is currently pointing to the
+    /// "ghost" non-element.
+    #[unstable(feature = "btree_cursors", issue = "107540")]
+    pub fn value(&self) -> Option<&'a V> {
+        self.current.as_ref().map(|current| current.into_kv().1)
+    }
+
+    /// Returns a reference to the key and value of the element that the cursor
+    /// is currently pointing to.
+    ///
+    /// This returns `None` if the cursor is currently pointing to the
+    /// "ghost" non-element.
+    #[unstable(feature = "btree_cursors", issue = "107540")]
+    pub fn key_value(&self) -> Option<(&'a K, &'a V)> {
+        self.current.as_ref().map(|current| current.into_kv())
+    }
+
+    /// Returns a reference to the next element.
+    ///
+    /// If the cursor is pointing to the "ghost" non-element then this returns
+    /// the first element of the `BTreeMap`. If it is pointing to the last
+    /// element of the `BTreeMap` then this returns `None`.
+    #[unstable(feature = "btree_cursors", issue = "107540")]
+    pub fn peek_next(&self) -> Option<(&'a K, &'a V)> {
+        let mut next = self.clone();
+        next.move_next();
+        next.current.as_ref().map(|current| current.into_kv())
+    }
+
+    /// Returns a reference to the previous element.
+    ///
+    /// If the cursor is pointing to the "ghost" non-element then this returns
+    /// the last element of the `BTreeMap`. If it is pointing to the first
+    /// element of the `BTreeMap` then this returns `None`.
+    #[unstable(feature = "btree_cursors", issue = "107540")]
+    pub fn peek_prev(&self) -> Option<(&'a K, &'a V)> {
+        let mut prev = self.clone();
+        prev.move_prev();
+        prev.current.as_ref().map(|current| current.into_kv())
+    }
+}
+
+impl<'a, K, V, A> CursorMut<'a, K, V, A> {
+    /// Moves the cursor to the next element of the `BTreeMap`.
+    ///
+    /// If the cursor is pointing to the "ghost" non-element then this will move it to
+    /// the first element of the `BTreeMap`. If it is pointing to the last
+    /// element of the `BTreeMap` then this will move it to the "ghost" non-element.
+    #[unstable(feature = "btree_cursors", issue = "107540")]
+    pub fn move_next(&mut self) {
+        match self.current.take() {
+            None => {
+                // SAFETY: The previous borrow of root has ended.
+                self.current = unsafe { self.root.reborrow() }.as_mut().and_then(|root| {
+                    root.borrow_mut().first_leaf_edge().forget_node_type().right_kv().ok()
+                });
+            }
+            Some(current) => {
+                self.current = current.next_leaf_edge().next_kv().ok();
+            }
+        }
+    }
+
+    /// Moves the cursor to the previous element of the `BTreeMap`.
+    ///
+    /// If the cursor is pointing to the "ghost" non-element then this will move it to
+    /// the last element of the `BTreeMap`. If it is pointing to the first
+    /// element of the `BTreeMap` then this will move it to the "ghost" non-element.
+    #[unstable(feature = "btree_cursors", issue = "107540")]
+    pub fn move_prev(&mut self) {
+        match self.current.take() {
+            None => {
+                // SAFETY: The previous borrow of root has ended.
+                self.current = unsafe { self.root.reborrow() }.as_mut().and_then(|root| {
+                    root.borrow_mut().last_leaf_edge().forget_node_type().left_kv().ok()
+                });
+            }
+            Some(current) => {
+                self.current = current.next_back_leaf_edge().next_back_kv().ok();
+            }
+        }
+    }
+
+    /// Returns a reference to the key of the element that the cursor is
+    /// currently pointing to.
+    ///
+    /// This returns `None` if the cursor is currently pointing to the
+    /// "ghost" non-element.
+    #[unstable(feature = "btree_cursors", issue = "107540")]
+    pub fn key(&self) -> Option<&K> {
+        self.current.as_ref().map(|current| current.reborrow().into_kv().0)
+    }
+
+    /// Returns a reference to the value of the element that the cursor is
+    /// currently pointing to.
+    ///
+    /// This returns `None` if the cursor is currently pointing to the
+    /// "ghost" non-element.
+    #[unstable(feature = "btree_cursors", issue = "107540")]
+    pub fn value(&self) -> Option<&V> {
+        self.current.as_ref().map(|current| current.reborrow().into_kv().1)
+    }
+
+    /// Returns a reference to the key and value of the element that the cursor
+    /// is currently pointing to.
+    ///
+    /// This returns `None` if the cursor is currently pointing to the
+    /// "ghost" non-element.
+    #[unstable(feature = "btree_cursors", issue = "107540")]
+    pub fn key_value(&self) -> Option<(&K, &V)> {
+        self.current.as_ref().map(|current| current.reborrow().into_kv())
+    }
+
+    /// Returns a mutable reference to the value of the element that the cursor
+    /// is currently pointing to.
+    ///
+    /// This returns `None` if the cursor is currently pointing to the
+    /// "ghost" non-element.
+    #[unstable(feature = "btree_cursors", issue = "107540")]
+    pub fn value_mut(&mut self) -> Option<&mut V> {
+        self.current.as_mut().map(|current| current.kv_mut().1)
+    }
+
+    /// Returns a reference to the key and mutable reference to the value of the
+    /// element that the cursor is currently pointing to.
+    ///
+    /// This returns `None` if the cursor is currently pointing to the
+    /// "ghost" non-element.
+    #[unstable(feature = "btree_cursors", issue = "107540")]
+    pub fn key_value_mut(&mut self) -> Option<(&K, &mut V)> {
+        self.current.as_mut().map(|current| {
+            let (k, v) = current.kv_mut();
+            (&*k, v)
+        })
+    }
+
+    /// Returns a mutable reference to the of the element that the cursor is
+    /// currently pointing to.
+    ///
+    /// This returns `None` if the cursor is currently pointing to the
+    /// "ghost" non-element.
+    ///
+    /// # Safety
+    ///
+    /// This can be used to modify the key, but you must ensure that the
+    /// `BTreeMap` invariants are maintained. Specifically:
+    ///
+    /// * The key must remain unique within the tree.
+    /// * The key must remain in sorted order with regards to other elements in
+    ///   the tree.
+    #[unstable(feature = "btree_cursors", issue = "107540")]
+    pub unsafe fn key_mut_unchecked(&mut self) -> Option<&mut K> {
+        self.current.as_mut().map(|current| current.kv_mut().0)
+    }
+
+    /// Returns a reference to the key and value of the next element.
+    ///
+    /// If the cursor is pointing to the "ghost" non-element then this returns
+    /// the first element of the `BTreeMap`. If it is pointing to the last
+    /// element of the `BTreeMap` then this returns `None`.
+    #[unstable(feature = "btree_cursors", issue = "107540")]
+    pub fn peek_next(&mut self) -> Option<(&K, &mut V)> {
+        let (k, v) = match self.current {
+            None => {
+                // SAFETY: The previous borrow of root has ended.
+                unsafe { self.root.reborrow() }
+                    .as_mut()?
+                    .borrow_mut()
+                    .first_leaf_edge()
+                    .next_kv()
+                    .ok()?
+                    .into_kv_valmut()
+            }
+            // SAFETY: We're not using this to mutate the tree.
+            Some(ref mut current) => {
+                unsafe { current.reborrow_mut() }.next_leaf_edge().next_kv().ok()?.into_kv_valmut()
+            }
+        };
+        Some((k, v))
+    }
+
+    /// Returns a reference to the key and value of the previous element.
+    ///
+    /// If the cursor is pointing to the "ghost" non-element then this returns
+    /// the last element of the `BTreeMap`. If it is pointing to the first
+    /// element of the `BTreeMap` then this returns `None`.
+    #[unstable(feature = "btree_cursors", issue = "107540")]
+    pub fn peek_prev(&mut self) -> Option<(&K, &mut V)> {
+        let (k, v) = match self.current.as_mut() {
+            None => {
+                // SAFETY: The previous borrow of root has ended.
+                unsafe { self.root.reborrow() }
+                    .as_mut()?
+                    .borrow_mut()
+                    .first_leaf_edge()
+                    .next_kv()
+                    .ok()?
+                    .into_kv_valmut()
+            }
+            Some(current) => {
+                // SAFETY: We're not using this to mutate the tree.
+                unsafe { current.reborrow_mut() }
+                    .next_back_leaf_edge()
+                    .next_back_kv()
+                    .ok()?
+                    .into_kv_valmut()
+            }
+        };
+        Some((k, v))
+    }
+
+    /// Returns a read-only cursor pointing to the current element.
+    ///
+    /// The lifetime of the returned `Cursor` is bound to that of the
+    /// `CursorMut`, which means it cannot outlive the `CursorMut` and that the
+    /// `CursorMut` is frozen for the lifetime of the `Cursor`.
+    #[unstable(feature = "btree_cursors", issue = "107540")]
+    pub fn as_cursor(&self) -> Cursor<'_, K, V> {
+        Cursor {
+            // SAFETY: The tree is immutable while the cursor exists.
+            root: unsafe { self.root.reborrow_shared().as_ref() },
+            current: self.current.as_ref().map(|current| current.reborrow()),
+        }
+    }
+}
+
+// Now the tree editing operations
+impl<'a, K: Ord, V, A: Allocator + Clone> CursorMut<'a, K, V, A> {
+    /// Inserts a new element into the `BTreeMap` after the current one.
+    ///
+    /// If the cursor is pointing at the "ghost" non-element then the new element is
+    /// inserted at the front of the `BTreeMap`.
+    ///
+    /// # Safety
+    ///
+    /// You must ensure that the `BTreeMap` invariants are maintained.
+    /// Specifically:
+    ///
+    /// * The key of the newly inserted element must be unique in the tree.
+    /// * All keys in the tree must remain in sorted order.
+    #[unstable(feature = "btree_cursors", issue = "107540")]
+    pub unsafe fn insert_after_unchecked(&mut self, key: K, value: V) {
+        let edge = match self.current.take() {
+            None => {
+                // SAFETY: We have no other reference to the tree.
+                match unsafe { self.root.reborrow() } {
+                    root @ None => {
+                        // Tree is empty, allocate a new root.
+                        let mut node = NodeRef::new_leaf(self.alloc.clone());
+                        node.borrow_mut().push(key, value);
+                        *root = Some(node.forget_type());
+                        *self.length += 1;
+                        return;
+                    }
+                    Some(root) => root.borrow_mut().first_leaf_edge(),
+                }
+            }
+            Some(current) => current.next_leaf_edge(),
+        };
+
+        let handle = edge.insert_recursing(key, value, self.alloc.clone(), |ins| {
+            drop(ins.left);
+            // SAFETY: The handle to the newly inserted value is always on a
+            // leaf node, so adding a new root node doesn't invalidate it.
+            let root = unsafe { self.root.reborrow().as_mut().unwrap() };
+            root.push_internal_level(self.alloc.clone()).push(ins.kv.0, ins.kv.1, ins.right)
+        });
+        self.current = handle.left_edge().next_back_kv().ok();
+        *self.length += 1;
+    }
+
+    /// Inserts a new element into the `BTreeMap` before the current one.
+    ///
+    /// If the cursor is pointing at the "ghost" non-element then the new element is
+    /// inserted at the end of the `BTreeMap`.
+    ///
+    /// # Safety
+    ///
+    /// You must ensure that the `BTreeMap` invariants are maintained.
+    /// Specifically:
+    ///
+    /// * The key of the newly inserted element must be unique in the tree.
+    /// * All keys in the tree must remain in sorted order.
+    #[unstable(feature = "btree_cursors", issue = "107540")]
+    pub unsafe fn insert_before_unchecked(&mut self, key: K, value: V) {
+        let edge = match self.current.take() {
+            None => {
+                // SAFETY: We have no other reference to the tree.
+                match unsafe { self.root.reborrow() } {
+                    root @ None => {
+                        // Tree is empty, allocate a new root.
+                        let mut node = NodeRef::new_leaf(self.alloc.clone());
+                        node.borrow_mut().push(key, value);
+                        *root = Some(node.forget_type());
+                        *self.length += 1;
+                        return;
+                    }
+                    Some(root) => root.borrow_mut().last_leaf_edge(),
+                }
+            }
+            Some(current) => current.next_back_leaf_edge(),
+        };
+
+        let handle = edge.insert_recursing(key, value, self.alloc.clone(), |ins| {
+            drop(ins.left);
+            // SAFETY: The handle to the newly inserted value is always on a
+            // leaf node, so adding a new root node doesn't invalidate it.
+            let root = unsafe { self.root.reborrow().as_mut().unwrap() };
+            root.push_internal_level(self.alloc.clone()).push(ins.kv.0, ins.kv.1, ins.right)
+        });
+        self.current = handle.right_edge().next_kv().ok();
+        *self.length += 1;
+    }
+
+    /// Inserts a new element into the `BTreeMap` after the current one.
+    ///
+    /// If the cursor is pointing at the "ghost" non-element then the new element is
+    /// inserted at the front of the `BTreeMap`.
+    ///
+    /// # Panics
+    ///
+    /// This function panics if:
+    /// - the given key compares less than or equal to the current element (if
+    ///   any).
+    /// - the given key compares greater than or equal to the next element (if
+    ///   any).
+    #[unstable(feature = "btree_cursors", issue = "107540")]
+    pub fn insert_after(&mut self, key: K, value: V) {
+        if let Some(current) = self.key() {
+            if &key <= current {
+                panic!("key must be ordered above the current element");
+            }
+        }
+        if let Some((next, _)) = self.peek_prev() {
+            if &key >= next {
+                panic!("key must be ordered below the next element");
+            }
+        }
+        unsafe {
+            self.insert_after_unchecked(key, value);
+        }
+    }
+
+    /// Inserts a new element into the `BTreeMap` before the current one.
+    ///
+    /// If the cursor is pointing at the "ghost" non-element then the new element is
+    /// inserted at the end of the `BTreeMap`.
+    ///
+    /// # Panics
+    ///
+    /// This function panics if:
+    /// - the given key compares greater than or equal to the current element
+    ///   (if any).
+    /// - the given key compares less than or equal to the previous element (if
+    ///   any).
+    #[unstable(feature = "btree_cursors", issue = "107540")]
+    pub fn insert_before(&mut self, key: K, value: V) {
+        if let Some(current) = self.key() {
+            if &key >= current {
+                panic!("key must be ordered below the current element");
+            }
+        }
+        if let Some((prev, _)) = self.peek_prev() {
+            if &key <= prev {
+                panic!("key must be ordered above the previous element");
+            }
+        }
+        unsafe {
+            self.insert_before_unchecked(key, value);
+        }
+    }
+
+    /// Removes the current element from the `BTreeMap`.
+    ///
+    /// The element that was removed is returned, and the cursor is
+    /// moved to point to the next element in the `BTreeMap`.
+    ///
+    /// If the cursor is currently pointing to the "ghost" non-element then no element
+    /// is removed and `None` is returned. The cursor is not moved in this case.
+    #[unstable(feature = "btree_cursors", issue = "107540")]
+    pub fn remove_current(&mut self) -> Option<(K, V)> {
+        let current = self.current.take()?;
+        let mut emptied_internal_root = false;
+        let (kv, pos) =
+            current.remove_kv_tracking(|| emptied_internal_root = true, self.alloc.clone());
+        self.current = pos.next_kv().ok();
+        *self.length -= 1;
+        if emptied_internal_root {
+            // SAFETY: This is safe since current does not point within the now
+            // empty root node.
+            let root = unsafe { self.root.reborrow().as_mut().unwrap() };
+            root.pop_internal_level(self.alloc.clone());
+        }
+        Some(kv)
+    }
+
+    /// Removes the current element from the `BTreeMap`.
+    ///
+    /// The element that was removed is returned, and the cursor is
+    /// moved to point to the previous element in the `BTreeMap`.
+    ///
+    /// If the cursor is currently pointing to the "ghost" non-element then no element
+    /// is removed and `None` is returned. The cursor is not moved in this case.
+    #[unstable(feature = "btree_cursors", issue = "107540")]
+    pub fn remove_current_and_move_back(&mut self) -> Option<(K, V)> {
+        let current = self.current.take()?;
+        let mut emptied_internal_root = false;
+        let (kv, pos) =
+            current.remove_kv_tracking(|| emptied_internal_root = true, self.alloc.clone());
+        self.current = pos.next_back_kv().ok();
+        *self.length -= 1;
+        if emptied_internal_root {
+            // SAFETY: This is safe since current does not point within the now
+            // empty root node.
+            let root = unsafe { self.root.reborrow().as_mut().unwrap() };
+            root.pop_internal_level(self.alloc.clone());
+        }
+        Some(kv)
+    }
 }
 
 #[cfg(test)]

library/alloc/src/collections/btree/map/entry.rs

@@ -347,7 +347,7 @@ impl<'a, K: Ord, V, A: Allocator + Clone> VacantEntry<'a, K, V, A> {
     /// assert_eq!(map["poneyland"], 37);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
-    pub fn insert(self, value: V) -> &'a mut V {
+    pub fn insert(mut self, value: V) -> &'a mut V {
         let out_ptr = match self.handle {
             None => {
                 // SAFETY: There is no tree yet so no reference to it exists.
@@ -358,25 +358,27 @@ impl<'a, K: Ord, V, A: Allocator + Clone> VacantEntry<'a, K, V, A> {
                 map.length = 1;
                 val_ptr
             }
-            Some(handle) => match handle.insert_recursing(self.key, value, self.alloc.clone()) {
+            Some(handle) => {
-                (None, val_ptr) => {
+                let new_handle =
-                    // SAFETY: We have consumed self.handle.
+                    handle.insert_recursing(self.key, value, self.alloc.clone(), |ins| {
-                    let map = unsafe { self.dormant_map.awaken() };
+                        drop(ins.left);
-                    map.length += 1;
+                        // SAFETY: Pushing a new root node doesn't invalidate
-                    val_ptr
+                        // handles to existing nodes.
-                }
+                        let map = unsafe { self.dormant_map.reborrow() };
-                (Some(ins), val_ptr) => {
+                        let root = map.root.as_mut().unwrap(); // same as ins.left
-                    drop(ins.left);
+                        root.push_internal_level(self.alloc).push(ins.kv.0, ins.kv.1, ins.right)
-                    // SAFETY: We have consumed self.handle and dropped the
+                    });
-                    // remaining reference to the tree, ins.left.
+
-                    let map = unsafe { self.dormant_map.awaken() };
+                // Get the pointer to the value
-                    let root = map.root.as_mut().unwrap(); // same as ins.left
+                let val_ptr = new_handle.into_val_mut();
-                    root.push_internal_level(self.alloc).push(ins.kv.0, ins.kv.1, ins.right);
+
-                    map.length += 1;
+                // SAFETY: We have consumed self.handle.
-                    val_ptr
+                let map = unsafe { self.dormant_map.awaken() };
-                }
+                map.length += 1;
-            },
+                val_ptr
+            }
         };
+
         // Now that we have finished growing the tree using borrowed references,
         // dereference the pointer to a part of it, that we picked up along the way.
         unsafe { &mut *out_ptr }

library/alloc/src/collections/btree/map/tests.rs

@@ -2336,3 +2336,52 @@ fn from_array() {
     let unordered_duplicates = BTreeMap::from([(3, 4), (1, 2), (1, 2)]);
     assert_eq!(map, unordered_duplicates);
 }
+
+#[test]
+fn test_cursor() {
+    let map = BTreeMap::from([(1, 'a'), (2, 'b'), (3, 'c')]);
+
+    let mut cur = map.lower_bound(Bound::Unbounded);
+    assert_eq!(cur.key(), Some(&1));
+    cur.move_next();
+    assert_eq!(cur.key(), Some(&2));
+    assert_eq!(cur.peek_next(), Some((&3, &'c')));
+    cur.move_prev();
+    assert_eq!(cur.key(), Some(&1));
+    assert_eq!(cur.peek_prev(), None);
+
+    let mut cur = map.upper_bound(Bound::Excluded(&1));
+    assert_eq!(cur.key(), None);
+    cur.move_next();
+    assert_eq!(cur.key(), Some(&1));
+    cur.move_prev();
+    assert_eq!(cur.key(), None);
+    assert_eq!(cur.peek_prev(), Some((&3, &'c')));
+}
+
+#[test]
+fn test_cursor_mut() {
+    let mut map = BTreeMap::from([(1, 'a'), (3, 'c'), (5, 'e')]);
+    let mut cur = map.lower_bound_mut(Bound::Excluded(&3));
+    assert_eq!(cur.key(), Some(&5));
+    cur.insert_before(4, 'd');
+    assert_eq!(cur.key(), Some(&5));
+    assert_eq!(cur.peek_prev(), Some((&4, &mut 'd')));
+    cur.move_next();
+    assert_eq!(cur.key(), None);
+    cur.insert_before(6, 'f');
+    assert_eq!(cur.key(), None);
+    assert_eq!(cur.remove_current(), None);
+    assert_eq!(cur.key(), None);
+    cur.insert_after(0, '?');
+    assert_eq!(cur.key(), None);
+    assert_eq!(map, BTreeMap::from([(0, '?'), (1, 'a'), (3, 'c'), (4, 'd'), (5, 'e'), (6, 'f')]));
+
+    let mut cur = map.upper_bound_mut(Bound::Included(&5));
+    assert_eq!(cur.key(), Some(&5));
+    assert_eq!(cur.remove_current(), Some((5, 'e')));
+    assert_eq!(cur.key(), Some(&6));
+    assert_eq!(cur.remove_current_and_move_back(), Some((6, 'f')));
+    assert_eq!(cur.key(), Some(&4));
+    assert_eq!(map, BTreeMap::from([(0, '?'), (1, 'a'), (3, 'c'), (4, 'd')]));
+}

library/alloc/src/collections/btree/navigate.rs

@@ -4,6 +4,7 @@ use core::ops::RangeBounds;
 use core::ptr;
 
 use super::node::{marker, ForceResult::*, Handle, NodeRef};
+use super::search::SearchBound;
 
 use crate::alloc::Allocator;
 // `front` and `back` are always both `None` or both `Some`.
@@ -386,7 +387,7 @@ impl<BorrowType: marker::BorrowType, K, V>
     /// Given a leaf edge handle, returns [`Result::Ok`] with a handle to the neighboring KV
     /// on the left side, which is either in the same leaf node or in an ancestor node.
     /// If the leaf edge is the first one in the tree, returns [`Result::Err`] with the root node.
-    fn next_back_kv(
+    pub fn next_back_kv(
         self,
     ) -> Result<
         Handle<NodeRef<BorrowType, K, V, marker::LeafOrInternal>, marker::KV>,
@@ -707,7 +708,9 @@ impl<BorrowType: marker::BorrowType, K, V>
     }
 
     /// Returns the leaf edge closest to a KV for backward navigation.
-    fn next_back_leaf_edge(self) -> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge> {
+    pub fn next_back_leaf_edge(
+        self,
+    ) -> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge> {
         match self.force() {
             Leaf(leaf_kv) => leaf_kv.left_edge(),
             Internal(internal_kv) => {
@@ -717,3 +720,51 @@ impl<BorrowType: marker::BorrowType, K, V>
         }
     }
 }
+
+impl<BorrowType: marker::BorrowType, K, V> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
+    /// Returns the leaf edge corresponding to the first point at which the
+    /// given bound is true.
+    pub fn lower_bound<Q: ?Sized>(
+        self,
+        mut bound: SearchBound<&Q>,
+    ) -> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge>
+    where
+        Q: Ord,
+        K: Borrow<Q>,
+    {
+        let mut node = self;
+        loop {
+            let (edge, new_bound) = node.find_lower_bound_edge(bound);
+            match edge.force() {
+                Leaf(edge) => return edge,
+                Internal(edge) => {
+                    node = edge.descend();
+                    bound = new_bound;
+                }
+            }
+        }
+    }
+
+    /// Returns the leaf edge corresponding to the last point at which the
+    /// given bound is true.
+    pub fn upper_bound<Q: ?Sized>(
+        self,
+        mut bound: SearchBound<&Q>,
+    ) -> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge>
+    where
+        Q: Ord,
+        K: Borrow<Q>,
+    {
+        let mut node = self;
+        loop {
+            let (edge, new_bound) = node.find_upper_bound_edge(bound);
+            match edge.force() {
+                Leaf(edge) => return edge,
+                Internal(edge) => {
+                    node = edge.descend();
+                    bound = new_bound;
+                }
+            }
+        }
+    }
+}

library/alloc/src/collections/btree/node.rs

@@ -442,6 +442,24 @@ impl<'a, K, V, Type> NodeRef<marker::Mut<'a>, K, V, Type> {
         // SAFETY: we have exclusive access to the entire node.
         unsafe { &mut *ptr }
     }
+
+    /// Returns a dormant copy of this node with its lifetime erased which can
+    /// be reawakened later.
+    pub fn dormant(&self) -> NodeRef<marker::DormantMut, K, V, Type> {
+        NodeRef { height: self.height, node: self.node, _marker: PhantomData }
+    }
+}
+
+impl<K, V, Type> NodeRef<marker::DormantMut, K, V, Type> {
+    /// Revert to the unique borrow initially captured.
+    ///
+    /// # Safety
+    ///
+    /// The reborrow must have ended, i.e., the reference returned by `new` and
+    /// all pointers and references derived from it, must not be used anymore.
+    pub unsafe fn awaken<'a>(self) -> NodeRef<marker::Mut<'a>, K, V, Type> {
+        NodeRef { height: self.height, node: self.node, _marker: PhantomData }
+    }
 }
 
 impl<K, V, Type> NodeRef<marker::Dying, K, V, Type> {
@@ -798,6 +816,25 @@ impl<'a, K, V, NodeType, HandleType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeT
         // We can't use Handle::new_kv or Handle::new_edge because we don't know our type
         Handle { node: unsafe { self.node.reborrow_mut() }, idx: self.idx, _marker: PhantomData }
     }
+
+    /// Returns a dormant copy of this handle which can be reawakened later.
+    ///
+    /// See `DormantMutRef` for more details.
+    pub fn dormant(&self) -> Handle<NodeRef<marker::DormantMut, K, V, NodeType>, HandleType> {
+        Handle { node: self.node.dormant(), idx: self.idx, _marker: PhantomData }
+    }
+}
+
+impl<K, V, NodeType, HandleType> Handle<NodeRef<marker::DormantMut, K, V, NodeType>, HandleType> {
+    /// Revert to the unique borrow initially captured.
+    ///
+    /// # Safety
+    ///
+    /// The reborrow must have ended, i.e., the reference returned by `new` and
+    /// all pointers and references derived from it, must not be used anymore.
+    pub unsafe fn awaken<'a>(self) -> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>, HandleType> {
+        Handle { node: unsafe { self.node.awaken() }, idx: self.idx, _marker: PhantomData }
+    }
 }
 
 impl<BorrowType, K, V, NodeType> Handle<NodeRef<BorrowType, K, V, NodeType>, marker::Edge> {
@@ -851,9 +888,11 @@ impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, mark
     /// Inserts a new key-value pair between the key-value pairs to the right and left of
     /// this edge. This method assumes that there is enough space in the node for the new
     /// pair to fit.
-    ///
+    unsafe fn insert_fit(
-    /// The returned pointer points to the inserted value.
+        mut self,
-    fn insert_fit(&mut self, key: K, val: V) -> *mut V {
+        key: K,
+        val: V,
+    ) -> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::KV> {
         debug_assert!(self.node.len() < CAPACITY);
         let new_len = self.node.len() + 1;
 
@@ -862,7 +901,7 @@ impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, mark
             slice_insert(self.node.val_area_mut(..new_len), self.idx, val);
             *self.node.len_mut() = new_len as u16;
 
-            self.node.val_area_mut(self.idx).assume_init_mut()
+            Handle::new_kv(self.node, self.idx)
         }
     }
 }
@@ -871,21 +910,26 @@ impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, mark
     /// Inserts a new key-value pair between the key-value pairs to the right and left of
     /// this edge. This method splits the node if there isn't enough room.
     ///
-    /// The returned pointer points to the inserted value.
+    /// Returns a dormant handle to the inserted node which can be reawakened
+    /// once splitting is complete.
     fn insert<A: Allocator + Clone>(
-        mut self,
+        self,
         key: K,
         val: V,
         alloc: A,
-    ) -> (Option<SplitResult<'a, K, V, marker::Leaf>>, *mut V) {
+    ) -> (
+        Option<SplitResult<'a, K, V, marker::Leaf>>,
+        Handle<NodeRef<marker::DormantMut, K, V, marker::Leaf>, marker::KV>,
+    ) {
         if self.node.len() < CAPACITY {
-            let val_ptr = self.insert_fit(key, val);
+            // SAFETY: There is enough space in the node for insertion.
-            (None, val_ptr)
+            let handle = unsafe { self.insert_fit(key, val) };
+            (None, handle.dormant())
         } else {
             let (middle_kv_idx, insertion) = splitpoint(self.idx);
             let middle = unsafe { Handle::new_kv(self.node, middle_kv_idx) };
             let mut result = middle.split(alloc);
-            let mut insertion_edge = match insertion {
+            let insertion_edge = match insertion {
                 LeftOrRight::Left(insert_idx) => unsafe {
                     Handle::new_edge(result.left.reborrow_mut(), insert_idx)
                 },
@@ -893,8 +937,10 @@ impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, mark
                     Handle::new_edge(result.right.borrow_mut(), insert_idx)
                 },
             };
-            let val_ptr = insertion_edge.insert_fit(key, val);
+            // SAFETY: We just split the node, so there is enough space for
-            (Some(result), val_ptr)
+            // insertion.
+            let handle = unsafe { insertion_edge.insert_fit(key, val).dormant() };
+            (Some(result), handle)
         }
     }
 }
@@ -976,21 +1022,31 @@ impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, mark
         key: K,
         value: V,
         alloc: A,
-    ) -> (Option<SplitResult<'a, K, V, marker::LeafOrInternal>>, *mut V) {
+        split_root: impl FnOnce(SplitResult<'a, K, V, marker::LeafOrInternal>),
-        let (mut split, val_ptr) = match self.insert(key, value, alloc.clone()) {
+    ) -> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::KV> {
-            (None, val_ptr) => return (None, val_ptr),
+        let (mut split, handle) = match self.insert(key, value, alloc.clone()) {
-            (Some(split), val_ptr) => (split.forget_node_type(), val_ptr),
+            // SAFETY: we have finished splitting and can now re-awaken the
+            // handle to the inserted element.
+            (None, handle) => return unsafe { handle.awaken() },
+            (Some(split), handle) => (split.forget_node_type(), handle),
         };
 
         loop {
             split = match split.left.ascend() {
                 Ok(parent) => {
                     match parent.insert(split.kv.0, split.kv.1, split.right, alloc.clone()) {
-                        None => return (None, val_ptr),
+                        // SAFETY: we have finished splitting and can now re-awaken the
+                        // handle to the inserted element.
+                        None => return unsafe { handle.awaken() },
                         Some(split) => split.forget_node_type(),
                     }
                 }
-                Err(root) => return (Some(SplitResult { left: root, ..split }), val_ptr),
+                Err(root) => {
+                    split_root(SplitResult { left: root, ..split });
+                    // SAFETY: we have finished splitting and can now re-awaken the
+                    // handle to the inserted element.
+                    return unsafe { handle.awaken() };
+                }
             };
         }
     }
@@ -1043,6 +1099,14 @@ impl<'a, K: 'a, V: 'a, NodeType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>
         let leaf = self.node.into_leaf_mut();
         unsafe { leaf.vals.get_unchecked_mut(self.idx).assume_init_mut() }
     }
+
+    pub fn into_kv_valmut(self) -> (&'a K, &'a mut V) {
+        debug_assert!(self.idx < self.node.len());
+        let leaf = self.node.into_leaf_mut();
+        let k = unsafe { leaf.keys.get_unchecked(self.idx).assume_init_ref() };
+        let v = unsafe { leaf.vals.get_unchecked_mut(self.idx).assume_init_mut() };
+        (k, v)
+    }
 }
 
 impl<'a, K, V, NodeType> Handle<NodeRef<marker::ValMut<'a>, K, V, NodeType>, marker::KV> {
@@ -1667,6 +1731,7 @@ pub mod marker {
 
     pub enum Owned {}
     pub enum Dying {}
+    pub enum DormantMut {}
     pub struct Immut<'a>(PhantomData<&'a ()>);
     pub struct Mut<'a>(PhantomData<&'a mut ()>);
     pub struct ValMut<'a>(PhantomData<&'a mut ()>);
@@ -1688,6 +1753,7 @@ pub mod marker {
     impl<'a> BorrowType for Immut<'a> {}
     impl<'a> BorrowType for Mut<'a> {}
     impl<'a> BorrowType for ValMut<'a> {}
+    impl BorrowType for DormantMut {}
 
     pub enum KV {}
     pub enum Edge {}

library/std/src/io/error.rs

@@ -102,7 +102,7 @@ enum ErrorData<C> {
 /// portability.
 ///
 /// [`into`]: Into::into
-#[unstable(feature = "raw_os_error_ty", issue = "none")]
+#[unstable(feature = "raw_os_error_ty", issue = "107792")]
 pub type RawOsError = i32;
 
 // `#[repr(align(4))]` is probably redundant, it should have that value or

library/std/src/io/mod.rs

@@ -262,7 +262,7 @@ use crate::sys_common::memchr;
 
 #[stable(feature = "bufwriter_into_parts", since = "1.56.0")]
 pub use self::buffered::WriterPanicked;
-#[unstable(feature = "raw_os_error_ty", issue = "none")]
+#[unstable(feature = "raw_os_error_ty", issue = "107792")]
 pub use self::error::RawOsError;
 pub(crate) use self::stdio::attempt_print_to_stderr;
 #[unstable(feature = "internal_output_capture", issue = "none")]

src/librustdoc/json/mod.rs

@@ -222,7 +222,7 @@ impl<'tcx> FormatRenderer<'tcx> for JsonRenderer<'tcx> {
     fn after_krate(&mut self) -> Result<(), Error> {
         debug!("Done with crate");
 
-        debug!("Adding Primitve impls");
+        debug!("Adding Primitive impls");
         for primitive in Rc::clone(&self.cache).primitive_locations.values() {
             self.get_impls(*primitive);
         }

tests/ui/macros/stringify.rs

@@ -626,7 +626,7 @@ fn test_item() {
         stringify_item!(
             impl ~const Struct {}
         ),
-        "impl Struct {}", // FIXME
+        "impl ~const Struct {}",
     );
 
     // ItemKind::MacCall
@@ -838,7 +838,7 @@ fn test_ty() {
     assert_eq!(stringify_ty!(dyn Send + 'a), "dyn Send + 'a");
     assert_eq!(stringify_ty!(dyn 'a + Send), "dyn 'a + Send");
     assert_eq!(stringify_ty!(dyn ?Sized), "dyn ?Sized");
-    assert_eq!(stringify_ty!(dyn ~const Clone), "dyn Clone"); // FIXME
+    assert_eq!(stringify_ty!(dyn ~const Clone), "dyn ~const Clone");
     assert_eq!(stringify_ty!(dyn for<'a> Send), "dyn for<'a> Send");
 
     // TyKind::ImplTrait
@@ -846,7 +846,7 @@ fn test_ty() {
     assert_eq!(stringify_ty!(impl Send + 'a), "impl Send + 'a");
     assert_eq!(stringify_ty!(impl 'a + Send), "impl 'a + Send");
     assert_eq!(stringify_ty!(impl ?Sized), "impl ?Sized");
-    assert_eq!(stringify_ty!(impl ~const Clone), "impl Clone"); // FIXME
+    assert_eq!(stringify_ty!(impl ~const Clone), "impl ~const Clone");
     assert_eq!(stringify_ty!(impl for<'a> Send), "impl for<'a> Send");
 
     // TyKind::Paren

tests/ui/rfc-2632-const-trait-impl/const_derives/derive-const-with-params.rs

@@ -0,0 +1,13 @@
+// check-pass
+
+#![feature(derive_const)]
+#![feature(const_trait_impl)]
+
+#[derive_const(PartialEq)]
+pub struct Reverse<T>(T);
+
+const fn foo(a: Reverse<i32>, b: Reverse<i32>) -> bool {
+    a == b
+}
+
+fn main() {}

tests/ui/unpretty/ast-const-trait-bound.rs

@@ -0,0 +1,4 @@
+// compile-flags: -Zunpretty=normal
+// check-pass
+
+fn foo() where T: ~const Bar {}

tests/ui/unpretty/ast-const-trait-bound.stdout

@@ -0,0 +1,4 @@
+// compile-flags: -Zunpretty=normal
+// check-pass
+
+fn foo() where T: ~const Bar {}