merge BorrowKind::Unique into BorrowKind::Mut

compiler/rustc_borrowck/src/borrow_set.rs

@@ -72,7 +72,7 @@ impl<'tcx> fmt::Display for BorrowData<'tcx> {
         let kind = match self.kind {
             mir::BorrowKind::Shared => "",
             mir::BorrowKind::Shallow => "shallow ",
-            mir::BorrowKind::Unique => "uniq ",
+            mir::BorrowKind::Mut { kind: mir::MutBorrowKind::ClosureCapture } => "uniq ",
             mir::BorrowKind::Mut { .. } => "mut ",
         };
         write!(w, "&{:?} {}{:?}", self.region, kind, self.borrowed_place)

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -15,8 +15,9 @@ use rustc_middle::hir::nested_filter::OnlyBodies;
 use rustc_middle::mir::tcx::PlaceTy;
 use rustc_middle::mir::{
     self, AggregateKind, BindingForm, BorrowKind, CallSource, ClearCrossCrate, ConstraintCategory,
-    FakeReadCause, LocalDecl, LocalInfo, LocalKind, Location, Operand, Place, PlaceRef,
+    FakeReadCause, LocalDecl, LocalInfo, LocalKind, Location, MutBorrowKind, Operand, Place,
-    ProjectionElem, Rvalue, Statement, StatementKind, Terminator, TerminatorKind, VarBindingForm,
+    PlaceRef, ProjectionElem, Rvalue, Statement, StatementKind, Terminator, TerminatorKind,
+    VarBindingForm,
 };
 use rustc_middle::ty::{self, suggest_constraining_type_params, PredicateKind, Ty};
 use rustc_middle::util::CallKind;
@@ -926,7 +927,10 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         // FIXME: supply non-"" `opt_via` when appropriate
         let first_borrow_desc;
         let mut err = match (gen_borrow_kind, issued_borrow.kind) {
-            (BorrowKind::Shared, BorrowKind::Mut { .. }) => {
+            (
+                BorrowKind::Shared,
+                BorrowKind::Mut { kind: MutBorrowKind::Default | MutBorrowKind::TwoPhaseBorrow },
+            ) => {
                 first_borrow_desc = "mutable ";
                 self.cannot_reborrow_already_borrowed(
                     span,
@@ -940,7 +944,10 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     None,
                 )
             }
-            (BorrowKind::Mut { .. }, BorrowKind::Shared) => {
+            (
+                BorrowKind::Mut { kind: MutBorrowKind::Default | MutBorrowKind::TwoPhaseBorrow },
+                BorrowKind::Shared,
+            ) => {
                 first_borrow_desc = "immutable ";
                 let mut err = self.cannot_reborrow_already_borrowed(
                     span,
@@ -962,7 +969,10 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 err
             }
 
-            (BorrowKind::Mut { .. }, BorrowKind::Mut { .. }) => {
+            (
+                BorrowKind::Mut { kind: MutBorrowKind::Default | MutBorrowKind::TwoPhaseBorrow },
+                BorrowKind::Mut { kind: MutBorrowKind::Default | MutBorrowKind::TwoPhaseBorrow },
+            ) => {
                 first_borrow_desc = "first ";
                 let mut err = self.cannot_mutably_borrow_multiply(
                     span,
@@ -985,12 +995,15 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 err
             }
 
-            (BorrowKind::Unique, BorrowKind::Unique) => {
+            (
+                BorrowKind::Mut { kind: MutBorrowKind::ClosureCapture },
+                BorrowKind::Mut { kind: MutBorrowKind::ClosureCapture },
+            ) => {
                 first_borrow_desc = "first ";
                 self.cannot_uniquely_borrow_by_two_closures(span, &desc_place, issued_span, None)
             }
 
-            (BorrowKind::Mut { .. } | BorrowKind::Unique, BorrowKind::Shallow) => {
+            (BorrowKind::Mut { .. }, BorrowKind::Shallow) => {
                 if let Some(immutable_section_description) =
                     self.classify_immutable_section(issued_borrow.assigned_place)
                 {
@@ -1004,7 +1017,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     borrow_spans.var_subdiag(
                         None,
                         &mut err,
-                        Some(BorrowKind::Unique),
+                        Some(BorrowKind::Mut { kind: MutBorrowKind::ClosureCapture }),
                         |kind, var_span| {
                             use crate::session_diagnostics::CaptureVarCause::*;
                             match kind {
@@ -1038,7 +1051,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 }
             }
 
-            (BorrowKind::Unique, _) => {
+            (BorrowKind::Mut { kind: MutBorrowKind::ClosureCapture }, _) => {
                 first_borrow_desc = "first ";
                 self.cannot_uniquely_borrow_by_one_closure(
                     span,
@@ -1052,7 +1065,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 )
             }
 
-            (BorrowKind::Shared, BorrowKind::Unique) => {
+            (BorrowKind::Shared, BorrowKind::Mut { kind: MutBorrowKind::ClosureCapture }) => {
                 first_borrow_desc = "first ";
                 self.cannot_reborrow_already_uniquely_borrowed(
                     span,
@@ -1067,7 +1080,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 )
             }
 
-            (BorrowKind::Mut { .. }, BorrowKind::Unique) => {
+            (BorrowKind::Mut { .. }, BorrowKind::Mut { kind: MutBorrowKind::ClosureCapture }) => {
                 first_borrow_desc = "first ";
                 self.cannot_reborrow_already_uniquely_borrowed(
                     span,
@@ -1085,10 +1098,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             (BorrowKind::Shared, BorrowKind::Shared | BorrowKind::Shallow)
             | (
                 BorrowKind::Shallow,
-                BorrowKind::Mut { .. }
+                BorrowKind::Mut { .. } | BorrowKind::Shared | BorrowKind::Shallow,
-                | BorrowKind::Unique
-                | BorrowKind::Shared
-                | BorrowKind::Shallow,
             ) => unreachable!(),
         };
 

compiler/rustc_borrowck/src/diagnostics/mod.rs

@@ -629,9 +629,9 @@ impl UseSpans<'_> {
                     Some(kd) => match kd {
                         rustc_middle::mir::BorrowKind::Shared
                         | rustc_middle::mir::BorrowKind::Shallow
-                        | rustc_middle::mir::BorrowKind::Unique => {
+                        | rustc_middle::mir::BorrowKind::Mut {
-                            CaptureVarKind::Immut { kind_span: capture_kind_span }
+                            kind: rustc_middle::mir::MutBorrowKind::ClosureCapture,
-                        }
+                        } => CaptureVarKind::Immut { kind_span: capture_kind_span },
 
                         rustc_middle::mir::BorrowKind::Mut { .. } => {
                             CaptureVarKind::Mut { kind_span: capture_kind_span }

compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs

@@ -234,7 +234,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
                     borrow_spans.var_subdiag(
                     None,
                     &mut err,
-                    Some(mir::BorrowKind::Mut { allow_two_phase_borrow: false }),
+                    Some(mir::BorrowKind::Mut { kind: mir::MutBorrowKind::Default }),
                     |_kind, var_span| {
                         let place = self.describe_any_place(access_place.as_ref());
                         crate::session_diagnostics::CaptureVarCause::MutableBorrowUsePlaceClosure {
@@ -300,7 +300,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
                             _,
                             mir::Rvalue::Ref(
                                 _,
-                                mir::BorrowKind::Mut { allow_two_phase_borrow: false },
+                                mir::BorrowKind::Mut { kind: mir::MutBorrowKind::Default },
                                 _,
                             ),
                         )),

compiler/rustc_borrowck/src/invalidation.rs

@@ -255,7 +255,7 @@ impl<'cx, 'tcx> InvalidationGenerator<'cx, 'tcx> {
                         (Shallow(Some(ArtificialField::ShallowBorrow)), Read(ReadKind::Borrow(bk)))
                     }
                     BorrowKind::Shared => (Deep, Read(ReadKind::Borrow(bk))),
-                    BorrowKind::Unique | BorrowKind::Mut { .. } => {
+                    BorrowKind::Mut { .. } => {
                         let wk = WriteKind::MutableBorrow(bk);
                         if allow_two_phase_borrow(bk) {
                             (Deep, Reservation(wk))
@@ -273,7 +273,7 @@ impl<'cx, 'tcx> InvalidationGenerator<'cx, 'tcx> {
                     Mutability::Mut => (
                         Deep,
                         Write(WriteKind::MutableBorrow(BorrowKind::Mut {
-                            allow_two_phase_borrow: false,
+                            kind: mir::MutBorrowKind::Default,
                         })),
                     ),
                     Mutability::Not => (Deep, Read(ReadKind::Borrow(BorrowKind::Shared))),
@@ -376,14 +376,11 @@ impl<'cx, 'tcx> InvalidationGenerator<'cx, 'tcx> {
                     }
 
                     (Read(_), BorrowKind::Shallow | BorrowKind::Shared)
-                    | (
+                    | (Read(ReadKind::Borrow(BorrowKind::Shallow)), BorrowKind::Mut { .. }) => {
-                        Read(ReadKind::Borrow(BorrowKind::Shallow)),
-                        BorrowKind::Unique | BorrowKind::Mut { .. },
-                    ) => {
                         // Reads don't invalidate shared or shallow borrows
                     }
 
-                    (Read(_), BorrowKind::Unique | BorrowKind::Mut { .. }) => {
+                    (Read(_), BorrowKind::Mut { .. }) => {
                         // Reading from mere reservations of mutable-borrows is OK.
                         if !is_active(&this.dominators, borrow, location) {
                             // If the borrow isn't active yet, reads don't invalidate it
@@ -425,7 +422,7 @@ impl<'cx, 'tcx> InvalidationGenerator<'cx, 'tcx> {
             // only mutable borrows should be 2-phase
             assert!(match borrow.kind {
                 BorrowKind::Shared | BorrowKind::Shallow => false,
-                BorrowKind::Unique | BorrowKind::Mut { .. } => true,
+                BorrowKind::Mut { .. } => true,
             });
 
             self.access_place(

compiler/rustc_borrowck/src/lib.rs

@@ -29,8 +29,8 @@ use rustc_infer::infer::{
     InferCtxt, NllRegionVariableOrigin, RegionVariableOrigin, TyCtxtInferExt,
 };
 use rustc_middle::mir::{
-    traversal, Body, ClearCrossCrate, Local, Location, Mutability, NonDivergingIntrinsic, Operand,
+    traversal, Body, ClearCrossCrate, Local, Location, MutBorrowKind, Mutability,
-    Place, PlaceElem, PlaceRef, VarDebugInfoContents,
+    NonDivergingIntrinsic, Operand, Place, PlaceElem, PlaceRef, VarDebugInfoContents,
 };
 use rustc_middle::mir::{AggregateKind, BasicBlock, BorrowCheckResult, BorrowKind};
 use rustc_middle::mir::{InlineAsmOperand, Terminator, TerminatorKind};
@@ -1071,10 +1071,9 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 }
 
                 (Read(_), BorrowKind::Shared | BorrowKind::Shallow)
-                | (
+                | (Read(ReadKind::Borrow(BorrowKind::Shallow)), BorrowKind::Mut { .. }) => {
-                    Read(ReadKind::Borrow(BorrowKind::Shallow)),
+                    Control::Continue
-                    BorrowKind::Unique | BorrowKind::Mut { .. },
+                }
-                ) => Control::Continue,
 
                 (Reservation(_), BorrowKind::Shallow | BorrowKind::Shared) => {
                     // This used to be a future compatibility warning (to be
@@ -1087,7 +1086,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     Control::Continue
                 }
 
-                (Read(kind), BorrowKind::Unique | BorrowKind::Mut { .. }) => {
+                (Read(kind), BorrowKind::Mut { .. }) => {
                     // Reading from mere reservations of mutable-borrows is OK.
                     if !is_active(this.dominators(), borrow, location) {
                         assert!(allow_two_phase_borrow(borrow.kind));
@@ -1194,7 +1193,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                         (Shallow(Some(ArtificialField::ShallowBorrow)), Read(ReadKind::Borrow(bk)))
                     }
                     BorrowKind::Shared => (Deep, Read(ReadKind::Borrow(bk))),
-                    BorrowKind::Unique | BorrowKind::Mut { .. } => {
+                    BorrowKind::Mut { .. } => {
                         let wk = WriteKind::MutableBorrow(bk);
                         if allow_two_phase_borrow(bk) {
                             (Deep, Reservation(wk))
@@ -1231,7 +1230,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                     Mutability::Mut => (
                         Deep,
                         Write(WriteKind::MutableBorrow(BorrowKind::Mut {
-                            allow_two_phase_borrow: false,
+                            kind: MutBorrowKind::Default,
                         })),
                     ),
                     Mutability::Not => (Deep, Read(ReadKind::Borrow(BorrowKind::Shared))),
@@ -1565,7 +1564,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             // only mutable borrows should be 2-phase
             assert!(match borrow.kind {
                 BorrowKind::Shared | BorrowKind::Shallow => false,
-                BorrowKind::Unique | BorrowKind::Mut { .. } => true,
+                BorrowKind::Mut { .. } => true,
             });
 
             self.access_place(
@@ -1959,14 +1958,12 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         let the_place_err;
 
         match kind {
-            Reservation(WriteKind::MutableBorrow(
+            Reservation(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Mut { .. }))
-                borrow_kind @ (BorrowKind::Unique | BorrowKind::Mut { .. }),
+            | Write(WriteKind::MutableBorrow(borrow_kind @ BorrowKind::Mut { .. })) => {
-            ))
-            | Write(WriteKind::MutableBorrow(
-                borrow_kind @ (BorrowKind::Unique | BorrowKind::Mut { .. }),
-            )) => {
                 let is_local_mutation_allowed = match borrow_kind {
-                    BorrowKind::Unique => LocalMutationIsAllowed::Yes,
+                    BorrowKind::Mut { kind: MutBorrowKind::ClosureCapture } => {
+                        LocalMutationIsAllowed::Yes
+                    }
                     BorrowKind::Mut { .. } => is_local_mutation_allowed,
                     BorrowKind::Shared | BorrowKind::Shallow => unreachable!(),
                 };
@@ -2031,12 +2028,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 return false;
             }
             Read(
-                ReadKind::Borrow(
+                ReadKind::Borrow(BorrowKind::Mut { .. } | BorrowKind::Shared | BorrowKind::Shallow)
-                    BorrowKind::Unique
-                    | BorrowKind::Mut { .. }
-                    | BorrowKind::Shared
-                    | BorrowKind::Shallow,
-                )
                 | ReadKind::Copy,
             ) => {
                 // Access authorized

compiler/rustc_borrowck/src/places_conflict.rs

@@ -4,7 +4,9 @@ use crate::ArtificialField;
 use crate::Overlap;
 use crate::{AccessDepth, Deep, Shallow};
 use rustc_hir as hir;
-use rustc_middle::mir::{Body, BorrowKind, Local, Place, PlaceElem, PlaceRef, ProjectionElem};
+use rustc_middle::mir::{
+    Body, BorrowKind, Local, MutBorrowKind, Place, PlaceElem, PlaceRef, ProjectionElem,
+};
 use rustc_middle::ty::{self, TyCtxt};
 use std::cmp::max;
 use std::iter;
@@ -35,7 +37,7 @@ pub fn places_conflict<'tcx>(
         tcx,
         body,
         borrow_place,
-        BorrowKind::Mut { allow_two_phase_borrow: true },
+        BorrowKind::Mut { kind: MutBorrowKind::TwoPhaseBorrow },
         access_place.as_ref(),
         AccessDepth::Deep,
         bias,

compiler/rustc_const_eval/src/transform/check_consts/check.rs

@@ -412,7 +412,6 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                         BorrowKind::Shallow => {
                             PlaceContext::NonMutatingUse(NonMutatingUseContext::ShallowBorrow)
                         }
-                        BorrowKind::Unique => PlaceContext::MutatingUse(MutatingUseContext::Borrow),
                         BorrowKind::Mut { .. } => {
                             PlaceContext::MutatingUse(MutatingUseContext::Borrow)
                         }
@@ -457,7 +456,7 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
                 }
             }
 
-            Rvalue::Ref(_, kind @ (BorrowKind::Mut { .. } | BorrowKind::Unique), place) => {
+            Rvalue::Ref(_, kind @ BorrowKind::Mut { .. }, place) => {
                 let ty = place.ty(self.body, self.tcx).ty;
                 let is_allowed = match ty.kind() {
                     // Inside a `static mut`, `&mut [...]` is allowed.

compiler/rustc_const_eval/src/transform/check_consts/resolver.rs

@@ -103,7 +103,7 @@ where
     fn ref_allows_mutation(&self, kind: mir::BorrowKind, place: mir::Place<'tcx>) -> bool {
         match kind {
             mir::BorrowKind::Mut { .. } => true,
-            mir::BorrowKind::Shared | mir::BorrowKind::Shallow | mir::BorrowKind::Unique => {
+            mir::BorrowKind::Shared | mir::BorrowKind::Shallow => {
                 self.shared_borrow_allows_mutation(place)
             }
         }

compiler/rustc_const_eval/src/transform/promote_consts.rs

@@ -454,7 +454,9 @@ impl<'tcx> Validator<'_, 'tcx> {
         match kind {
             // Reject these borrow types just to be safe.
             // FIXME(RalfJung): could we allow them? Should we? No point in it until we have a usecase.
-            BorrowKind::Shallow | BorrowKind::Unique => return Err(Unpromotable),
+            BorrowKind::Shallow | BorrowKind::Mut { kind: MutBorrowKind::ClosureCapture } => {
+                return Err(Unpromotable);
+            }
 
             BorrowKind::Shared => {
                 let has_mut_interior = self.qualif_local::<qualifs::HasMutInterior>(place.local);

compiler/rustc_middle/src/mir/mod.rs

@@ -2035,22 +2035,24 @@ impl<'tcx> Rvalue<'tcx> {
 impl BorrowKind {
     pub fn mutability(&self) -> Mutability {
         match *self {
-            BorrowKind::Shared | BorrowKind::Shallow | BorrowKind::Unique => Mutability::Not,
+            BorrowKind::Shared | BorrowKind::Shallow => Mutability::Not,
             BorrowKind::Mut { .. } => Mutability::Mut,
         }
     }
 
     pub fn allows_two_phase_borrow(&self) -> bool {
         match *self {
-            BorrowKind::Shared | BorrowKind::Shallow | BorrowKind::Unique => false,
+            BorrowKind::Shared | BorrowKind::Shallow => false,
-            BorrowKind::Mut { allow_two_phase_borrow } => allow_two_phase_borrow,
+            BorrowKind::Mut { kind } => kind == MutBorrowKind::TwoPhaseBorrow,
         }
     }
 
     // FIXME: won't be used after diagnostic migration
     pub fn describe_mutability(&self) -> &str {
         match *self {
-            BorrowKind::Shared | BorrowKind::Shallow | BorrowKind::Unique => "immutable",
+            BorrowKind::Shared
+            | BorrowKind::Shallow
+            | BorrowKind::Mut { kind: MutBorrowKind::ClosureCapture } => "immutable",
             BorrowKind::Mut { .. } => "mutable",
         }
     }
@@ -2090,7 +2092,7 @@ impl<'tcx> Debug for Rvalue<'tcx> {
                 let kind_str = match borrow_kind {
                     BorrowKind::Shared => "",
                     BorrowKind::Shallow => "shallow ",
-                    BorrowKind::Mut { .. } | BorrowKind::Unique => "mut ",
+                    BorrowKind::Mut { .. } => "mut ",
                 };
 
                 // When printing regions, add trailing space if necessary.

compiler/rustc_middle/src/mir/syntax.rs

@@ -182,6 +182,16 @@ pub enum BorrowKind {
     /// We can also report errors with this kind of borrow differently.
     Shallow,
 
+    /// Data is mutable and not aliasable.
+    Mut { kind: MutBorrowKind },
+}
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, TyEncodable, TyDecodable)]
+#[derive(Hash, HashStable)]
+pub enum MutBorrowKind {
+    Default,
+    /// this borrow arose from method-call auto-ref. (i.e., `adjustment::Adjust::Borrow`)
+    TwoPhaseBorrow,
     /// Data must be immutable but not aliasable. This kind of borrow
     /// cannot currently be expressed by the user and is used only in
     /// implicit closure bindings. It is needed when the closure is
@@ -220,19 +230,7 @@ pub enum BorrowKind {
     /// immutable, but not aliasable. This solves the problem. For
     /// simplicity, we don't give users the way to express this
     /// borrow, it's just used when translating closures.
-    ///
+    ClosureCapture,
-    // FIXME(#112072): This is wrong. Unique borrows are mutable borrows except
-    // that they do not require their pointee to be marked as a mutable.
-    // They should still be treated as mutable borrows in every other way,
-    // e.g. for variance or overlap checking.
-    Unique,
-
-    /// Data is mutable and not aliasable.
-    Mut {
-        /// `true` if this borrow arose from method-call auto-ref
-        /// (i.e., `adjustment::Adjust::Borrow`).
-        allow_two_phase_borrow: bool,
-    },
 }
 
 ///////////////////////////////////////////////////////////////////////////

compiler/rustc_middle/src/mir/tcx.rs

@@ -269,11 +269,6 @@ impl BorrowKind {
             BorrowKind::Mut { .. } => hir::Mutability::Mut,
             BorrowKind::Shared => hir::Mutability::Not,
 
-            // We have no type corresponding to a unique imm borrow, so
-            // use `&mut`. It gives all the capabilities of a `&uniq`
-            // and hence is a safe "over approximation".
-            BorrowKind::Unique => hir::Mutability::Mut,
-
             // We have no type corresponding to a shallow borrow, so use
             // `&` as an approximation.
             BorrowKind::Shallow => hir::Mutability::Not,

compiler/rustc_middle/src/mir/visit.rs

@@ -650,9 +650,6 @@ macro_rules! make_mir_visitor {
                             BorrowKind::Shallow => PlaceContext::NonMutatingUse(
                                 NonMutatingUseContext::ShallowBorrow
                             ),
-                            BorrowKind::Unique => PlaceContext::MutatingUse(
-                                MutatingUseContext::Borrow
-                            ),
                             BorrowKind::Mut { .. } =>
                                 PlaceContext::MutatingUse(MutatingUseContext::Borrow),
                         };

compiler/rustc_mir_build/src/build/expr/as_rvalue.rs

@@ -442,7 +442,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                                 match upvar.kind {
                                     ExprKind::Borrow {
                                         borrow_kind:
-                                            BorrowKind::Mut { allow_two_phase_borrow: false },
+                                            BorrowKind::Mut { kind: MutBorrowKind::Default },
                                         arg,
                                     } => unpack!(
                                         block = this.limit_capture_mutability(
@@ -795,8 +795,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         };
 
         let borrow_kind = match mutability {
-            Mutability::Not => BorrowKind::Unique,
+            Mutability::Not => BorrowKind::Mut { kind: MutBorrowKind::ClosureCapture },
-            Mutability::Mut => BorrowKind::Mut { allow_two_phase_borrow: false },
+            Mutability::Mut => BorrowKind::Mut { kind: MutBorrowKind::Default },
         };
 
         let arg_place = arg_place_builder.to_place(this);

compiler/rustc_mir_build/src/check_unsafety.rs

@@ -3,7 +3,7 @@ use crate::errors::*;
 use rustc_middle::thir::visit::{self, Visitor};
 
 use rustc_hir as hir;
-use rustc_middle::mir::BorrowKind;
+use rustc_middle::mir::{BorrowKind, MutBorrowKind};
 use rustc_middle::thir::*;
 use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_middle::ty::{self, ParamEnv, Ty, TyCtxt};
@@ -254,7 +254,9 @@ impl<'a, 'tcx> Visitor<'a, 'tcx> for UnsafetyVisitor<'a, 'tcx> {
                         );
                     };
                     match borrow_kind {
-                        BorrowKind::Shallow | BorrowKind::Shared | BorrowKind::Unique => {
+                        BorrowKind::Shallow
+                        | BorrowKind::Shared
+                        | BorrowKind::Mut { kind: MutBorrowKind::ClosureCapture } => {
                             if !ty.is_freeze(self.tcx, self.param_env) {
                                 self.requires_unsafe(pat.span, BorrowOfLayoutConstrainedField);
                             }
@@ -440,15 +442,19 @@ impl<'a, 'tcx> Visitor<'a, 'tcx> for UnsafetyVisitor<'a, 'tcx> {
                 visit::walk_expr(&mut visitor, expr);
                 if visitor.found {
                     match borrow_kind {
-                        BorrowKind::Shallow | BorrowKind::Shared | BorrowKind::Unique
+                        BorrowKind::Shallow
+                        | BorrowKind::Shared
+                        | BorrowKind::Mut { kind: MutBorrowKind::ClosureCapture }
                             if !self.thir[arg].ty.is_freeze(self.tcx, self.param_env) =>
                         {
                             self.requires_unsafe(expr.span, BorrowOfLayoutConstrainedField)
                         }
-                        BorrowKind::Mut { .. } => {
+                        BorrowKind::Mut {
-                            self.requires_unsafe(expr.span, MutationOfLayoutConstrainedField)
+                            kind: MutBorrowKind::Default | MutBorrowKind::TwoPhaseBorrow,
-                        }
+                        } => self.requires_unsafe(expr.span, MutationOfLayoutConstrainedField),
-                        BorrowKind::Shallow | BorrowKind::Shared | BorrowKind::Unique => {}
+                        BorrowKind::Shallow
+                        | BorrowKind::Shared
+                        | BorrowKind::Mut { kind: MutBorrowKind::ClosureCapture } => {}
                     }
                 }
             }

compiler/rustc_mir_build/src/thir/cx/expr.rs

@@ -1095,8 +1095,12 @@ impl<'tcx> Cx<'tcx> {
             ty::UpvarCapture::ByRef(upvar_borrow) => {
                 let borrow_kind = match upvar_borrow {
                     ty::BorrowKind::ImmBorrow => BorrowKind::Shared,
-                    ty::BorrowKind::UniqueImmBorrow => BorrowKind::Unique,
+                    ty::BorrowKind::UniqueImmBorrow => {
-                    ty::BorrowKind::MutBorrow => BorrowKind::Mut { allow_two_phase_borrow: false },
+                        BorrowKind::Mut { kind: mir::MutBorrowKind::ClosureCapture }
+                    }
+                    ty::BorrowKind::MutBorrow => {
+                        BorrowKind::Mut { kind: mir::MutBorrowKind::Default }
+                    }
                 };
                 Expr {
                     temp_lifetime,
@@ -1132,9 +1136,9 @@ impl ToBorrowKind for AutoBorrowMutability {
         use rustc_middle::ty::adjustment::AllowTwoPhase;
         match *self {
             AutoBorrowMutability::Mut { allow_two_phase_borrow } => BorrowKind::Mut {
-                allow_two_phase_borrow: match allow_two_phase_borrow {
+                kind: match allow_two_phase_borrow {
-                    AllowTwoPhase::Yes => true,
+                    AllowTwoPhase::Yes => mir::MutBorrowKind::TwoPhaseBorrow,
-                    AllowTwoPhase::No => false,
+                    AllowTwoPhase::No => mir::MutBorrowKind::Default,
                 },
             },
             AutoBorrowMutability::Not => BorrowKind::Shared,
@@ -1145,7 +1149,7 @@ impl ToBorrowKind for AutoBorrowMutability {
 impl ToBorrowKind for hir::Mutability {
     fn to_borrow_kind(&self) -> BorrowKind {
         match *self {
-            hir::Mutability::Mut => BorrowKind::Mut { allow_two_phase_borrow: false },
+            hir::Mutability::Mut => BorrowKind::Mut { kind: mir::MutBorrowKind::Default },
             hir::Mutability::Not => BorrowKind::Shared,
         }
     }

compiler/rustc_mir_build/src/thir/pattern/mod.rs

@@ -287,7 +287,7 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
                     ty::BindByValue(mutbl) => (mutbl, BindingMode::ByValue),
                     ty::BindByReference(hir::Mutability::Mut) => (
                         Mutability::Not,
-                        BindingMode::ByRef(BorrowKind::Mut { allow_two_phase_borrow: false }),
+                        BindingMode::ByRef(BorrowKind::Mut { kind: mir::MutBorrowKind::Default }),
                     ),
                     ty::BindByReference(hir::Mutability::Not) => {
                         (Mutability::Not, BindingMode::ByRef(BorrowKind::Shared))

compiler/rustc_mir_dataflow/src/elaborate_drops.rs

@@ -638,7 +638,7 @@ where
                 Place::from(ref_place),
                 Rvalue::Ref(
                     tcx.lifetimes.re_erased,
-                    BorrowKind::Mut { allow_two_phase_borrow: false },
+                    BorrowKind::Mut { kind: MutBorrowKind::Default },
                     self.place,
                 ),
             )],

compiler/rustc_mir_transform/src/inline.rs

@@ -522,7 +522,7 @@ impl<'tcx> Inliner<'tcx> {
                     trace!("creating temp for return destination");
                     let dest = Rvalue::Ref(
                         self.tcx.lifetimes.re_erased,
-                        BorrowKind::Mut { allow_two_phase_borrow: false },
+                        BorrowKind::Mut { kind: MutBorrowKind::Default },
                         destination,
                     );
                     let dest_ty = dest.ty(caller_body, self.tcx);

compiler/rustc_mir_transform/src/shim.rs

@@ -188,7 +188,7 @@ fn build_drop_shim<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId, ty: Option<Ty<'tcx>>)
         // has been put into the body.
         let reborrow = Rvalue::Ref(
             tcx.lifetimes.re_erased,
-            BorrowKind::Mut { allow_two_phase_borrow: false },
+            BorrowKind::Mut { kind: MutBorrowKind::Default },
             tcx.mk_place_deref(dropee_ptr),
         );
         let ref_ty = reborrow.ty(body.local_decls(), tcx);
@@ -712,7 +712,7 @@ fn build_call_shim<'tcx>(
                 )
                 .immutable(),
             );
-            let borrow_kind = BorrowKind::Mut { allow_two_phase_borrow: false };
+            let borrow_kind = BorrowKind::Mut { kind: MutBorrowKind::Default };
             statements.push(Statement {
                 source_info,
                 kind: StatementKind::Assign(Box::new((