don't expose the borrows field

src/librustc_mir/borrow_check/flows.rs

@@ -14,25 +14,27 @@
 //! but is not as ugly as it is right now.
 
 use rustc::mir::{BasicBlock, Location};
+use rustc_data_structures::indexed_set::Iter;
 
 use dataflow::{MaybeInitializedPlaces, MaybeUninitializedPlaces};
 use dataflow::{EverInitializedPlaces, MovingOutStatements};
 use dataflow::{Borrows};
 use dataflow::{FlowAtLocation, FlowsAtLocation};
 use dataflow::move_paths::HasMoveData;
+use dataflow::move_paths::indexes::BorrowIndex;
 use std::fmt;
 
 // (forced to be `pub` due to its use as an associated type below.)
-pub(crate) struct Flows<'b, 'gcx: 'tcx, 'tcx: 'b> {
-    pub borrows: FlowAtLocation<Borrows<'b, 'gcx, 'tcx>>,
+crate struct Flows<'b, 'gcx: 'tcx, 'tcx: 'b> {
+    borrows: FlowAtLocation<Borrows<'b, 'gcx, 'tcx>>,
     pub inits: FlowAtLocation<MaybeInitializedPlaces<'b, 'gcx, 'tcx>>,
     pub uninits: FlowAtLocation<MaybeUninitializedPlaces<'b, 'gcx, 'tcx>>,
     pub move_outs: FlowAtLocation<MovingOutStatements<'b, 'gcx, 'tcx>>,
     pub ever_inits: FlowAtLocation<EverInitializedPlaces<'b, 'gcx, 'tcx>>,
 }
 
 impl<'b, 'gcx, 'tcx> Flows<'b, 'gcx, 'tcx> {
-    pub fn new(
+    crate fn new(
         borrows: FlowAtLocation<Borrows<'b, 'gcx, 'tcx>>,
         inits: FlowAtLocation<MaybeInitializedPlaces<'b, 'gcx, 'tcx>>,
         uninits: FlowAtLocation<MaybeUninitializedPlaces<'b, 'gcx, 'tcx>>,
@@ -47,6 +49,14 @@ impl<'b, 'gcx, 'tcx> Flows<'b, 'gcx, 'tcx> {
             ever_inits,
         }
     }
+
+    crate fn borrows_in_scope(&self) -> impl Iterator<Item = BorrowIndex> + '_ {
+        self.borrows.iter_incoming()
+    }
+
+    crate fn with_outgoing_borrows(&self, op: impl FnOnce(Iter<BorrowIndex>)) {
+        self.borrows.with_iter_outgoing(op)
+    }
 }
 
 macro_rules! each_flow {

src/librustc_mir/borrow_check/mod.rs

@@ -550,7 +550,7 @@ impl<'cx, 'gcx, 'tcx> DataflowResultsConsumer<'cx, 'tcx> for MirBorrowckCtxt<'cx
                 if self.movable_generator {
                     // Look for any active borrows to locals
                     let borrow_set = self.borrow_set.clone();
-                    flow_state.borrows.with_iter_outgoing(|borrows| {
+                    flow_state.with_outgoing_borrows(|borrows| {
                         for i in borrows {
                             let borrow = &borrow_set[i];
                             self.check_for_local_borrow(borrow, span);
@@ -565,7 +565,7 @@ impl<'cx, 'gcx, 'tcx> DataflowResultsConsumer<'cx, 'tcx> for MirBorrowckCtxt<'cx
                 // StorageDead, but we don't always emit those (notably on unwind paths),
                 // so this "extra check" serves as a kind of backup.
                 let borrow_set = self.borrow_set.clone();
-                flow_state.borrows.with_iter_outgoing(|borrows| {
+                flow_state.with_outgoing_borrows(|borrows| {
                     for i in borrows {
                         let borrow = &borrow_set[i];
                         let context = ContextKind::StorageDead.new(loc);
@@ -2224,10 +2224,9 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
         unreachable!("iter::repeat returned None")
     }
 
-    /// This function iterates over all of the current borrows
-    /// (represented by 1-bits in `flow_state.borrows`) that conflict
-    /// with an access to a place, invoking the `op` callback for each
-    /// one.
+    /// This function iterates over all of the in-scope borrows that
+    /// conflict with an access to a place, invoking the `op` callback
+    /// for each one.
     ///
     /// "Current borrow" here means a borrow that reaches the point in
     /// the control-flow where the access occurs.
@@ -2251,7 +2250,7 @@ impl<'cx, 'gcx, 'tcx> MirBorrowckCtxt<'cx, 'gcx, 'tcx> {
         // check for loan restricting path P being used. Accounts for
         // borrows of P, P.a.b, etc.
         let borrow_set = self.borrow_set.clone();
-        for i in flow_state.borrows.iter_incoming() {
+        for i in flow_state.borrows_in_scope() {
             let borrowed = &borrow_set[i];
 
             if self.places_conflict(&borrowed.borrowed_place, place, access) {