NLL: Limit two-phase borrows to autoref-introduced borrows

src/librustc/ich/impls_mir.rs

@@ -20,7 +20,6 @@ use std::mem;
 impl_stable_hash_for!(struct mir::GeneratorLayout<'tcx> { fields });
 impl_stable_hash_for!(struct mir::SourceInfo { span, scope });
 impl_stable_hash_for!(enum mir::Mutability { Mut, Not });
-impl_stable_hash_for!(enum mir::BorrowKind { Shared, Unique, Mut });
 impl_stable_hash_for!(enum mir::LocalKind { Var, Temp, Arg, ReturnPointer });
 impl_stable_hash_for!(struct mir::LocalDecl<'tcx> {
     mutability,
@@ -36,6 +35,25 @@ impl_stable_hash_for!(struct mir::BasicBlockData<'tcx> { statements, terminator,
 impl_stable_hash_for!(struct mir::UnsafetyViolation { source_info, description, kind });
 impl_stable_hash_for!(struct mir::UnsafetyCheckResult { violations, unsafe_blocks });
 
+impl<'gcx> HashStable<StableHashingContext<'gcx>>
+for mir::BorrowKind {
+    #[inline]
+    fn hash_stable<W: StableHasherResult>(&self,
+                                          hcx: &mut StableHashingContext<'gcx>,
+                                          hasher: &mut StableHasher<W>) {
+        mem::discriminant(self).hash_stable(hcx, hasher);
+
+        match *self {
+            mir::BorrowKind::Shared |
+            mir::BorrowKind::Unique => {}
+            mir::BorrowKind::Mut { allow_two_phase_borrow } => {
+                allow_two_phase_borrow.hash_stable(hcx, hasher);
+            }
+        }
+    }
+}
+
+
 impl<'gcx> HashStable<StableHashingContext<'gcx>>
 for mir::UnsafetyViolationKind {
     #[inline]

src/librustc/ich/impls_ty.rs

@@ -163,6 +163,20 @@ impl_stable_hash_for!(struct ty::adjustment::Adjustment<'tcx> { kind, target });
 impl_stable_hash_for!(struct ty::adjustment::OverloadedDeref<'tcx> { region, mutbl });
 impl_stable_hash_for!(struct ty::UpvarBorrow<'tcx> { kind, region });
 
+impl<'gcx> HashStable<StableHashingContext<'gcx>> for ty::adjustment::AutoBorrowMutability {
+    fn hash_stable<W: StableHasherResult>(&self,
+                                          hcx: &mut StableHashingContext<'gcx>,
+                                          hasher: &mut StableHasher<W>) {
+        mem::discriminant(self).hash_stable(hcx, hasher);
+        match *self {
+            ty::adjustment::AutoBorrowMutability::Mutable { ref allow_two_phase_borrow } => {
+                allow_two_phase_borrow.hash_stable(hcx, hasher);
+            }
+            ty::adjustment::AutoBorrowMutability::Immutable => {}
+        }
+    }
+}
+
 impl_stable_hash_for!(struct ty::UpvarId { var_id, closure_expr_id });
 
 impl_stable_hash_for!(enum ty::BorrowKind {

src/librustc/middle/expr_use_visitor.rs

@@ -760,7 +760,7 @@ impl<'a, 'gcx, 'tcx> ExprUseVisitor<'a, 'gcx, 'tcx> {
                                      expr.span,
                                      cmt_base,
                                      r,
-                                     ty::BorrowKind::from_mutbl(m),
+                                     ty::BorrowKind::from_mutbl(m.into()),
                                      AutoRef);
             }
 

src/librustc/mir/mod.rs

@@ -413,7 +413,20 @@ pub enum BorrowKind {
     Unique,
 
     /// Data is mutable and not aliasable.
-    Mut,
+    Mut {
+        /// True if this borrow arose from method-call auto-ref
+        /// (i.e. `adjustment::Adjust::Borrow`)
+        allow_two_phase_borrow: bool
+    }
+}
+
+impl BorrowKind {
+    pub fn allows_two_phase_borrow(&self) -> bool {
+        match *self {
+            BorrowKind::Shared | BorrowKind::Unique => false,
+            BorrowKind::Mut { allow_two_phase_borrow } => allow_two_phase_borrow,
+        }
+    }
 }
 
 ///////////////////////////////////////////////////////////////////////////
@@ -1611,7 +1624,7 @@ impl<'tcx> Debug for Rvalue<'tcx> {
             Ref(region, borrow_kind, ref place) => {
                 let kind_str = match borrow_kind {
                     BorrowKind::Shared => "",
-                    BorrowKind::Mut | BorrowKind::Unique => "mut ",
+                    BorrowKind::Mut { .. } | BorrowKind::Unique => "mut ",
                 };
 
                 // When printing regions, add trailing space if necessary.

src/librustc/mir/tcx.rs

@@ -264,7 +264,7 @@ impl<'tcx> BinOp {
 impl BorrowKind {
     pub fn to_mutbl_lossy(self) -> hir::Mutability {
         match self {
-            BorrowKind::Mut => hir::MutMutable,
+            BorrowKind::Mut { .. } => hir::MutMutable,
             BorrowKind::Shared => hir::MutImmutable,
 
             // We have no type corresponding to a unique imm borrow, so

src/librustc/mir/visit.rs

@@ -951,9 +951,10 @@ impl<'tcx> PlaceContext<'tcx> {
     pub fn is_mutating_use(&self) -> bool {
         match *self {
             PlaceContext::Store | PlaceContext::AsmOutput | PlaceContext::Call |
-            PlaceContext::Borrow { kind: BorrowKind::Mut, .. } |
+            PlaceContext::Borrow { kind: BorrowKind::Mut { .. }, .. } |
             PlaceContext::Projection(Mutability::Mut) |
             PlaceContext::Drop => true,
+
             PlaceContext::Inspect |
             PlaceContext::Borrow { kind: BorrowKind::Shared, .. } |
             PlaceContext::Borrow { kind: BorrowKind::Unique, .. } |
@@ -971,7 +972,8 @@ impl<'tcx> PlaceContext<'tcx> {
             PlaceContext::Borrow { kind: BorrowKind::Unique, .. } |
             PlaceContext::Projection(Mutability::Not) |
             PlaceContext::Copy | PlaceContext::Move => true,
-            PlaceContext::Borrow { kind: BorrowKind::Mut, .. } | PlaceContext::Store |
+
+            PlaceContext::Borrow { kind: BorrowKind::Mut { .. }, .. } | PlaceContext::Store |
             PlaceContext::AsmOutput |
             PlaceContext::Call | PlaceContext::Projection(Mutability::Mut) |
             PlaceContext::Drop | PlaceContext::StorageLive | PlaceContext::StorageDead |

src/librustc/session/config.rs

@@ -1085,6 +1085,8 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
         "select which borrowck is used (`ast`, `mir`, or `compare`)"),
     two_phase_borrows: bool = (false, parse_bool, [UNTRACKED],
         "use two-phase reserved/active distinction for `&mut` borrows in MIR borrowck"),
+    two_phase_beyond_autoref: bool = (false, parse_bool, [UNTRACKED],
+        "when using two-phase-borrows, allow two phases even for non-autoref `&mut` borrows"),
     time_passes: bool = (false, parse_bool, [UNTRACKED],
         "measure time of each rustc pass"),
     count_llvm_insns: bool = (false, parse_bool,

src/librustc/ty/adjustment.rs

@@ -119,10 +119,25 @@ impl<'a, 'gcx, 'tcx> OverloadedDeref<'tcx> {
     }
 }
 
+#[derive(Copy, Clone, PartialEq, Debug, RustcEncodable, RustcDecodable)]
+pub enum AutoBorrowMutability {
+    Mutable { allow_two_phase_borrow: bool },
+    Immutable,
+}
+
+impl From<AutoBorrowMutability> for hir::Mutability {
+    fn from(m: AutoBorrowMutability) -> Self {
+        match m {
+            AutoBorrowMutability::Mutable { .. } => hir::MutMutable,
+            AutoBorrowMutability::Immutable => hir::MutImmutable,
+        }
+    }
+}
+
 #[derive(Copy, Clone, PartialEq, Debug, RustcEncodable, RustcDecodable)]
 pub enum AutoBorrow<'tcx> {
     /// Convert from T to &T.
-    Ref(ty::Region<'tcx>, hir::Mutability),
+    Ref(ty::Region<'tcx>, AutoBorrowMutability),
 
     /// Convert from T to *T.
     RawPtr(hir::Mutability),

src/librustc_const_eval/pattern.rs

@@ -134,7 +134,7 @@ impl<'tcx> fmt::Display for Pattern<'tcx> {
                     BindingMode::ByValue => mutability == Mutability::Mut,
                     BindingMode::ByRef(_, bk) => {
                         write!(f, "ref ")?;
-                        bk == BorrowKind::Mut
+                        match bk { BorrowKind::Mut { .. } => true, _ => false }
                     }
                 };
                 if is_mut {
@@ -429,7 +429,7 @@ impl<'a, 'tcx> PatternContext<'a, 'tcx> {
                         (Mutability::Not, BindingMode::ByValue),
                     ty::BindByReference(hir::MutMutable) =>
                         (Mutability::Not, BindingMode::ByRef(
-                            region.unwrap(), BorrowKind::Mut)),
+                            region.unwrap(), BorrowKind::Mut { allow_two_phase_borrow: false })),
                     ty::BindByReference(hir::MutImmutable) =>
                         (Mutability::Not, BindingMode::ByRef(
                             region.unwrap(), BorrowKind::Shared)),

src/librustc_lint/unused.rs

@@ -437,8 +437,10 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedAllocation {
         for adj in cx.tables.expr_adjustments(e) {
             if let adjustment::Adjust::Borrow(adjustment::AutoBorrow::Ref(_, m)) = adj.kind {
                 let msg = match m {
-                    hir::MutImmutable => "unnecessary allocation, use & instead",
-                    hir::MutMutable => "unnecessary allocation, use &mut instead"
+                    adjustment::AutoBorrowMutability::Immutable =>
+                        "unnecessary allocation, use & instead",
+                    adjustment::AutoBorrowMutability::Mutable { .. }=>
+                        "unnecessary allocation, use &mut instead"
                 };
                 cx.span_lint(UNUSED_ALLOCATION, e.span, msg);
             }

src/librustc_mir/borrow_check/error_reporting.rs

@@ -256,8 +256,8 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
             "immutable",
             "mutable",
         ) {
-            (BorrowKind::Shared, lft, _, BorrowKind::Mut, _, rgt) |
-            (BorrowKind::Mut, _, lft, BorrowKind::Shared, rgt, _) => self.tcx
+            (BorrowKind::Shared, lft, _, BorrowKind::Mut { .. }, _, rgt) |
+            (BorrowKind::Mut { .. }, _, lft, BorrowKind::Shared, rgt, _) => self.tcx
                 .cannot_reborrow_already_borrowed(
                     span,
                     &desc_place,
@@ -271,7 +271,7 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
                     Origin::Mir,
                 ),
 
-            (BorrowKind::Mut, _, _, BorrowKind::Mut, _, _) => self.tcx
+            (BorrowKind::Mut { .. }, _, _, BorrowKind::Mut { .. }, _, _) => self.tcx
                 .cannot_mutably_borrow_multiply(
                     span,
                     &desc_place,
@@ -314,7 +314,7 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
                     Origin::Mir,
                 ),
 
-            (BorrowKind::Mut, _, lft, BorrowKind::Unique, _, _) => self.tcx
+            (BorrowKind::Mut { .. }, _, lft, BorrowKind::Unique, _, _) => self.tcx
                 .cannot_reborrow_already_uniquely_borrowed(
                     span,
                     &desc_place,

src/librustc_mir/borrow_check/mod.rs

@@ -707,6 +707,15 @@ impl InitializationRequiringAction {
 }
 
 impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
+    /// Returns true if the borrow represented by `kind` is
+    /// allowed to be split into separate Reservation and
+    /// Activation phases.
+    fn allow_two_phase_borrow(&self, kind: BorrowKind) -> bool {
+        self.tcx.sess.two_phase_borrows() &&
+            (kind.allows_two_phase_borrow() ||
+             self.tcx.sess.opts.debugging_opts.two_phase_beyond_autoref)
+    }
+
     /// Checks an access to the given place to see if it is allowed. Examines the set of borrows
     /// that are in scope, as well as which paths have been initialized, to ensure that (a) the
     /// place is initialized and (b) it is not borrowed in some way that would prevent this
@@ -797,9 +806,9 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
                     Control::Continue
                 }
 
-                (Read(kind), BorrowKind::Unique) | (Read(kind), BorrowKind::Mut) => {
+                (Read(kind), BorrowKind::Unique) | (Read(kind), BorrowKind::Mut { .. }) => {
                     // Reading from mere reservations of mutable-borrows is OK.
-                    if this.tcx.sess.two_phase_borrows() && index.is_reservation()
+                    if this.allow_two_phase_borrow(borrow.kind) && index.is_reservation()
                     {
                         return Control::Continue;
                     }
@@ -828,7 +837,7 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
                 }
 
                 (Reservation(kind), BorrowKind::Unique)
-                | (Reservation(kind), BorrowKind::Mut)
+                | (Reservation(kind), BorrowKind::Mut { .. })
                 | (Activation(kind, _), _)
                 | (Write(kind), _) => {
                     match rw {
@@ -945,9 +954,9 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
             Rvalue::Ref(_ /*rgn*/, bk, ref place) => {
                 let access_kind = match bk {
                     BorrowKind::Shared => (Deep, Read(ReadKind::Borrow(bk))),
-                    BorrowKind::Unique | BorrowKind::Mut => {
+                    BorrowKind::Unique | BorrowKind::Mut { .. } => {
                         let wk = WriteKind::MutableBorrow(bk);
-                        if self.tcx.sess.two_phase_borrows() {
+                        if self.allow_two_phase_borrow(bk) {
                             (Deep, Reservation(wk))
                         } else {
                             (Deep, Write(wk))
@@ -1196,7 +1205,7 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
                 // mutable borrow before we check it.
                 match borrow.kind {
                     BorrowKind::Shared => return,
-                    BorrowKind::Unique | BorrowKind::Mut => {}
+                    BorrowKind::Unique | BorrowKind::Mut { .. } => {}
                 }
 
                 self.access_place(
@@ -1467,8 +1476,8 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
                     span_bug!(span, "&unique borrow for {:?} should not fail", place);
                 }
             }
-            Reservation(WriteKind::MutableBorrow(BorrowKind::Mut))
-            | Write(WriteKind::MutableBorrow(BorrowKind::Mut)) => if let Err(place_err) =
+            Reservation(WriteKind::MutableBorrow(BorrowKind::Mut { .. }))
+            | Write(WriteKind::MutableBorrow(BorrowKind::Mut { .. })) => if let Err(place_err) =
                 self.is_mutable(place, is_local_mutation_allowed)
             {
                 error_reported = true;
@@ -1532,7 +1541,7 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
             Activation(..) => {} // permission checks are done at Reservation point.
 
             Read(ReadKind::Borrow(BorrowKind::Unique))
-            | Read(ReadKind::Borrow(BorrowKind::Mut))
+            | Read(ReadKind::Borrow(BorrowKind::Mut { .. }))
             | Read(ReadKind::Borrow(BorrowKind::Shared))
             | Read(ReadKind::Copy) => {} // Access authorized
         }

src/librustc_mir/dataflow/impls/borrows.rs

@@ -122,7 +122,7 @@ impl<'tcx> fmt::Display for BorrowData<'tcx> {
         let kind = match self.kind {
             mir::BorrowKind::Shared => "",
             mir::BorrowKind::Unique => "uniq ",
-            mir::BorrowKind::Mut => "mut ",
+            mir::BorrowKind::Mut { .. } => "mut ",
         };
         let region = format!("{}", self.region);
         let region = if region.len() > 0 { format!("{} ", region) } else { region };

src/librustc_mir/hair/cx/expr.rs

@@ -17,10 +17,11 @@ use hair::cx::to_ref::ToRef;
 use rustc::hir::def::{Def, CtorKind};
 use rustc::middle::const_val::ConstVal;
 use rustc::ty::{self, AdtKind, VariantDef, Ty};
-use rustc::ty::adjustment::{Adjustment, Adjust, AutoBorrow};
+use rustc::ty::adjustment::{Adjustment, Adjust, AutoBorrow, AutoBorrowMutability};
 use rustc::ty::cast::CastKind as TyCastKind;
 use rustc::hir;
 use rustc::hir::def_id::LocalDefId;
+use rustc::mir::{BorrowKind};
 
 impl<'tcx> Mirror<'tcx> for &'tcx hir::Expr {
     type Output = Expr<'tcx>;
@@ -111,7 +112,7 @@ fn apply_adjustment<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
                 span,
                 kind: ExprKind::Borrow {
                     region: deref.region,
-                    borrow_kind: to_borrow_kind(deref.mutbl),
+                    borrow_kind: deref.mutbl.to_borrow_kind(),
                     arg: expr.to_ref(),
                 },
             };
@@ -121,7 +122,7 @@ fn apply_adjustment<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
         Adjust::Borrow(AutoBorrow::Ref(r, m)) => {
             ExprKind::Borrow {
                 region: r,
-                borrow_kind: to_borrow_kind(m),
+                borrow_kind: m.to_borrow_kind(),
                 arg: expr.to_ref(),
             }
         }
@@ -141,7 +142,7 @@ fn apply_adjustment<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
                 span,
                 kind: ExprKind::Borrow {
                     region,
-                    borrow_kind: to_borrow_kind(m),
+                    borrow_kind: m.to_borrow_kind(),
                     arg: expr.to_ref(),
                 },
             };
@@ -287,7 +288,7 @@ fn make_mirror_unadjusted<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
             };
             ExprKind::Borrow {
                 region,
-                borrow_kind: to_borrow_kind(mutbl),
+                borrow_kind: mutbl.to_borrow_kind(),
                 arg: expr.to_ref(),
             }
         }
@@ -642,10 +643,25 @@ fn method_callee<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
     }
 }
 
-fn to_borrow_kind(m: hir::Mutability) -> BorrowKind {
-    match m {
-        hir::MutMutable => BorrowKind::Mut,
-        hir::MutImmutable => BorrowKind::Shared,
+trait ToBorrowKind { fn to_borrow_kind(&self) -> BorrowKind; }
+
+impl ToBorrowKind for AutoBorrowMutability {
+    fn to_borrow_kind(&self) -> BorrowKind {
+        match *self {
+            AutoBorrowMutability::Mutable { allow_two_phase_borrow } =>
+                BorrowKind::Mut { allow_two_phase_borrow },
+            AutoBorrowMutability::Immutable =>
+                BorrowKind::Shared,
+        }
+    }
+}
+
+impl ToBorrowKind for hir::Mutability {
+    fn to_borrow_kind(&self) -> BorrowKind {
+        match *self {
+            hir::MutMutable => BorrowKind::Mut { allow_two_phase_borrow: false },
+            hir::MutImmutable => BorrowKind::Shared,
+        }
     }
 }
 
@@ -947,7 +963,7 @@ fn capture_freevar<'a, 'gcx, 'tcx>(cx: &mut Cx<'a, 'gcx, 'tcx>,
             let borrow_kind = match upvar_borrow.kind {
                 ty::BorrowKind::ImmBorrow => BorrowKind::Shared,
                 ty::BorrowKind::UniqueImmBorrow => BorrowKind::Unique,
-                ty::BorrowKind::MutBorrow => BorrowKind::Mut,
+                ty::BorrowKind::MutBorrow => BorrowKind::Mut { allow_two_phase_borrow: false }
             };
             Expr {
                 temp_lifetime,