adjust libcore

src/libcore/cell.rs

@@ -1084,9 +1084,11 @@ impl<'b, T: ?Sized> RefMut<'b, T> {
     pub fn map<U: ?Sized, F>(orig: RefMut<'b, T>, f: F) -> RefMut<'b, U>
         where F: FnOnce(&mut T) -> &mut U
     {
+        // FIXME: fix borrow-check
+        let RefMut { value, borrow } = orig;
         RefMut {
-            value: f(orig.value),
+            value: f(value),
-            borrow: orig.borrow,
+            borrow: borrow,
         }
     }
 }

src/libcore/iter/mod.rs

@@ -1776,14 +1776,20 @@ impl<I: Iterator> Iterator for Peekable<I> {
 
     #[inline]
     fn nth(&mut self, n: usize) -> Option<I::Item> {
+        // FIXME: merge these when borrow-checking gets better.
+        if n == 0 {
+            match self.peeked.take() {
+                Some(v) => v,
+                None => self.iter.nth(n),
+            }
+        } else {
             match self.peeked.take() {
-            // the .take() below is just to avoid "move into pattern guard"
-            Some(ref mut v) if n == 0 => v.take(),
                 Some(None) => None,
                 Some(Some(_)) => self.iter.nth(n - 1),
                 None => self.iter.nth(n),
             }
         }
+    }
 
     #[inline]
     fn last(mut self) -> Option<I::Item> {