add helper method to get base of place without projections

Author: csmoe

src/librustc/mir/tcx.rs

@@ -299,8 +299,13 @@ impl<'tcx> NeoPlace<'tcx> {
         }
     }
 
-    pub fn has_no_projection(&self) -> bool {
-        self.elems.is_empty()
+    // Return the base of place without projections
+    pub fn bare_place(&self) -> Option<&PlaceBase<'tcx>>{
+        if self.elems.is_empty() {
+            Some(&self.base)
+        } else {
+            None
+        }
     }
 }
 

src/librustc_mir/borrow_check/borrow_set.rs

@@ -346,15 +346,14 @@ impl<'a, 'gcx, 'tcx> GatherBorrows<'a, 'gcx, 'tcx> {
         //
         // so extract `temp`.
         let neo_place = self.tcx.as_new_place(assigned_place);
-        let temp = match neo_place.base {
-            mir::PlaceBase::Local(temp) if neo_place.has_no_projection() => temp,
-            _ => {
-                span_bug!(
-                    self.mir.source_info(start_location).span,
-                    "expected 2-phase borrow to assign to a local, not `{:?}`",
-                    assigned_place,
-                );
-            }
+        let temp = if let Some(mir::PlaceBase::Local(temp)) = neo_place.bare_place() {
+            *temp
+        } else {
+            span_bug!(
+                self.mir.source_info(start_location).span,
+                "expected 2-phase borrow to assign to a local, not `{:?}`",
+                assigned_place,
+            );
         };
 
         // Consider the borrow not activated to start. When we find an activation, we'll update