Make commit and rollback_to methods take ownership of the snapshots.

Because they shouldn't be reused. This provides consistency with the
`ena` crate.

Author: nnethercote

src/librustc/infer/mod.rs

@@ -790,7 +790,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
 
         self.projection_cache
             .borrow_mut()
-            .commit(&projection_cache_snapshot);
+            .commit(projection_cache_snapshot);
         self.type_variables.borrow_mut().commit(type_snapshot);
         self.int_unification_table.borrow_mut().commit(int_snapshot);
         self.float_unification_table

src/librustc/traits/project.rs

@@ -1652,15 +1652,15 @@ impl<'tcx> ProjectionCache<'tcx> {
     }
 
     pub fn rollback_to(&mut self, snapshot: ProjectionCacheSnapshot) {
-        self.map.rollback_to(&snapshot.snapshot);
+        self.map.rollback_to(snapshot.snapshot);
     }
 
     pub fn rollback_placeholder(&mut self, snapshot: &ProjectionCacheSnapshot) {
         self.map.partial_rollback(&snapshot.snapshot, &|k| k.ty.has_re_skol());
     }
 
-    pub fn commit(&mut self, snapshot: &ProjectionCacheSnapshot) {
-        self.map.commit(&snapshot.snapshot);
+    pub fn commit(&mut self, snapshot: ProjectionCacheSnapshot) {
+        self.map.commit(snapshot.snapshot);
     }
 
     /// Try to start normalize `key`; returns an error if

src/librustc_data_structures/snapshot_map/mod.rs

@@ -102,8 +102,8 @@ impl<K, V> SnapshotMap<K, V>
         });
     }
 
-    pub fn commit(&mut self, snapshot: &Snapshot) {
-        self.assert_open_snapshot(snapshot);
+    pub fn commit(&mut self, snapshot: Snapshot) {
+        self.assert_open_snapshot(&snapshot);
         if snapshot.len == 0 {
             // The root snapshot.
             self.undo_log.clear();
@@ -134,8 +134,8 @@ impl<K, V> SnapshotMap<K, V>
         }
     }
 
-    pub fn rollback_to(&mut self, snapshot: &Snapshot) {
-        self.assert_open_snapshot(snapshot);
+    pub fn rollback_to(&mut self, snapshot: Snapshot) {
+        self.assert_open_snapshot(&snapshot);
         while self.undo_log.len() > snapshot.len + 1 {
             let entry = self.undo_log.pop().unwrap();
             self.reverse(entry);

src/librustc_data_structures/snapshot_map/test.rs

@@ -20,7 +20,7 @@ fn basic() {
     map.insert(44, "fourty-four");
     assert_eq!(map[&44], "fourty-four");
     assert_eq!(map.get(&33), None);
-    map.rollback_to(&snapshot);
+    map.rollback_to(snapshot);
     assert_eq!(map[&22], "twenty-two");
     assert_eq!(map.get(&33), None);
     assert_eq!(map.get(&44), None);
@@ -33,7 +33,7 @@ fn out_of_order() {
     map.insert(22, "twenty-two");
     let snapshot1 = map.snapshot();
     let _snapshot2 = map.snapshot();
-    map.rollback_to(&snapshot1);
+    map.rollback_to(snapshot1);
 }
 
 #[test]
@@ -43,8 +43,8 @@ fn nested_commit_then_rollback() {
     let snapshot1 = map.snapshot();
     let snapshot2 = map.snapshot();
     map.insert(22, "thirty-three");
-    map.commit(&snapshot2);
+    map.commit(snapshot2);
     assert_eq!(map[&22], "thirty-three");
-    map.rollback_to(&snapshot1);
+    map.rollback_to(snapshot1);
     assert_eq!(map[&22], "twenty-two");
 }