review feedback: Use checked-arith instead of saturated-arith for push_unsafe! and pop_unsafe!.

Author: pnkfelix

src/librustc/middle/effect.rs

@@ -124,11 +124,11 @@ impl<'a, 'tcx, 'v> Visitor<'v> for EffectCheckVisitor<'a, 'tcx> {
             }
             ast::PushUnsafeBlock(..) => {
                 self.unsafe_context.push_unsafe_count =
-                    self.unsafe_context.push_unsafe_count.saturating_add(1);
+                    self.unsafe_context.push_unsafe_count.checked_add(1).unwrap();
             }
             ast::PopUnsafeBlock(..) => {
                 self.unsafe_context.push_unsafe_count =
-                    self.unsafe_context.push_unsafe_count.saturating_sub(1);
+                    self.unsafe_context.push_unsafe_count.checked_sub(1).unwrap();
             }
         }
 

src/librustc_typeck/check/mod.rs

@@ -251,9 +251,9 @@ impl UnsafetyState {
             unsafety => {
                 let (unsafety, def, count) = match blk.rules {
                     ast::PushUnsafeBlock(..) =>
-                        (unsafety, blk.id, self.unsafe_push_count.saturating_add(1)),
+                        (unsafety, blk.id, self.unsafe_push_count.checked_add(1).unwrap()),
                     ast::PopUnsafeBlock(..) =>
-                        (unsafety, blk.id, self.unsafe_push_count.saturating_sub(1)),
+                        (unsafety, blk.id, self.unsafe_push_count.checked_sub(1).unwrap()),
                     ast::UnsafeBlock(..) =>
                         (ast::Unsafety::Unsafe, blk.id, self.unsafe_push_count),
                     ast::DefaultBlock =>