Fix reverse iteration in cretonne-entity's Iter.

A `DoubleEndedIterator` needs to track both a forward position and a
reverse position, so that `next_back()` can pop from the back of the
sequence.

lib/entity/src/iter.rs

@@ -10,6 +10,7 @@ where
     V: 'a,
 {
     pos: usize,
+    rev_pos: usize,
     iter: slice::Iter<'a, V>,
     unused: PhantomData<K>,
 }
@@ -17,9 +18,10 @@ where
 impl<'a, K: EntityRef, V> Iter<'a, K, V> {
     /// Create an `Iter` iterator that visits the `PrimaryMap` keys and values
     /// of `iter`.
-    pub fn new(key: K, iter: slice::Iter<'a, V>) -> Self {
+    pub fn new(iter: slice::Iter<'a, V>) -> Self {
         Self {
-            pos: key.index(),
+            pos: 0,
+            rev_pos: iter.len(),
             iter,
             unused: PhantomData,
         }
@@ -47,7 +49,9 @@ impl<'a, K: EntityRef, V> Iterator for Iter<'a, K, V> {
 impl<'a, K: EntityRef, V> DoubleEndedIterator for Iter<'a, K, V> {
     fn next_back(&mut self) -> Option<Self::Item> {
         if let Some(next_back) = self.iter.next_back() {
-            Some((K::new(self.pos), next_back))
+            let rev_pos = self.rev_pos - 1;
+            self.rev_pos -= 1;
+            Some((K::new(rev_pos), next_back))
         } else {
             None
         }
@@ -62,6 +66,7 @@ where
     V: 'a,
 {
     pos: usize,
+    rev_pos: usize,
     iter: slice::IterMut<'a, V>,
     unused: PhantomData<K>,
 }
@@ -69,9 +74,10 @@ where
 impl<'a, K: EntityRef, V> IterMut<'a, K, V> {
     /// Create an `IterMut` iterator that visits the `PrimaryMap` keys and values
     /// of `iter`.
-    pub fn new(key: K, iter: slice::IterMut<'a, V>) -> Self {
+    pub fn new(iter: slice::IterMut<'a, V>) -> Self {
         Self {
-            pos: key.index(),
+            pos: 0,
+            rev_pos: iter.len(),
             iter,
             unused: PhantomData,
         }
@@ -99,7 +105,9 @@ impl<'a, K: EntityRef, V> Iterator for IterMut<'a, K, V> {
 impl<'a, K: EntityRef, V> DoubleEndedIterator for IterMut<'a, K, V> {
     fn next_back(&mut self) -> Option<Self::Item> {
         if let Some(next_back) = self.iter.next_back() {
-            Some((K::new(self.pos), next_back))
+            let rev_pos = self.rev_pos - 1;
+            self.rev_pos -= 1;
+            Some((K::new(rev_pos), next_back))
         } else {
             None
         }

lib/entity/src/keys.rs

@@ -11,11 +11,11 @@ pub struct Keys<K: EntityRef> {
 }
 
 impl<K: EntityRef> Keys<K> {
-    /// Create a `Keys` iterator that visits `count` entities starting from 0.
+    /// Create a `Keys` iterator that visits `len` entities starting from 0.
-    pub fn new(count: usize) -> Self {
+    pub fn with_len(len: usize) -> Self {
         Self {
             pos: 0,
-            rev_pos: count,
+            rev_pos: len,
             unused: PhantomData,
         }
     }

lib/entity/src/map.rs

@@ -71,17 +71,17 @@ where
 
     /// Iterate over all the keys and values in this map.
     pub fn iter(&self) -> Iter<K, V> {
-        Iter::new(K::new(0), self.elems.iter())
+        Iter::new(self.elems.iter())
     }
 
     /// Iterate over all the keys and values in this map, mutable edition.
     pub fn iter_mut(&mut self) -> IterMut<K, V> {
-        IterMut::new(K::new(0), self.elems.iter_mut())
+        IterMut::new(self.elems.iter_mut())
     }
 
     /// Iterate over all the keys in this map.
     pub fn keys(&self) -> Keys<K> {
-        Keys::new(self.elems.len())
+        Keys::with_len(self.elems.len())
     }
 
     /// Iterate over all the keys in this map.

lib/entity/src/primary.rs

@@ -57,7 +57,7 @@ where
 
     /// Iterate over all the keys in this map.
     pub fn keys(&self) -> Keys<K> {
-        Keys::new(self.elems.len())
+        Keys::with_len(self.elems.len())
     }
 
     /// Iterate over all the values in this map.
@@ -72,12 +72,12 @@ where
 
     /// Iterate over all the keys and values in this map.
     pub fn iter(&self) -> Iter<K, V> {
-        Iter::new(K::new(0), self.elems.iter())
+        Iter::new(self.elems.iter())
     }
 
     /// Iterate over all the keys and values in this map, mutable edition.
     pub fn iter_mut(&mut self) -> IterMut<K, V> {
-        IterMut::new(K::new(0), self.elems.iter_mut())
+        IterMut::new(self.elems.iter_mut())
     }
 
     /// Remove all entries from this map.
@@ -192,6 +192,34 @@ mod tests {
         }
     }
 
+    #[test]
+    fn iter_rev() {
+        let mut m: PrimaryMap<E, usize> = PrimaryMap::new();
+        m.push(12);
+        m.push(33);
+
+        let mut i = 2;
+        for (key, value) in m.iter().rev() {
+            i -= 1;
+            assert_eq!(key.index(), i);
+            match i {
+                0 => assert_eq!(*value, 12),
+                1 => assert_eq!(*value, 33),
+                _ => panic!(),
+            }
+        }
+
+        i = 2;
+        for (key, value) in m.iter_mut().rev() {
+            i -= 1;
+            assert_eq!(key.index(), i);
+            match i {
+                0 => assert_eq!(*value, 12),
+                1 => assert_eq!(*value, 33),
+                _ => panic!(),
+            }
+        }
+    }
     #[test]
     fn keys() {
         let mut m: PrimaryMap<E, usize> = PrimaryMap::new();
@@ -205,6 +233,19 @@ mod tests {
         }
     }
 
+    #[test]
+    fn keys_rev() {
+        let mut m: PrimaryMap<E, usize> = PrimaryMap::new();
+        m.push(12);
+        m.push(33);
+
+        let mut i = 2;
+        for key in m.keys().rev() {
+            i -= 1;
+            assert_eq!(key.index(), i);
+        }
+    }
+
     #[test]
     fn values() {
         let mut m: PrimaryMap<E, usize> = PrimaryMap::new();
@@ -230,4 +271,31 @@ mod tests {
             i += 1;
         }
     }
+
+    #[test]
+    fn values_rev() {
+        let mut m: PrimaryMap<E, usize> = PrimaryMap::new();
+        m.push(12);
+        m.push(33);
+
+        let mut i = 2;
+        for value in m.values().rev() {
+            i -= 1;
+            match i {
+                0 => assert_eq!(*value, 12),
+                1 => assert_eq!(*value, 33),
+                _ => panic!(),
+            }
+        }
+        i = 2;
+        for value_mut in m.values_mut().rev() {
+            i -= 1;
+            match i {
+                0 => assert_eq!(*value_mut, 12),
+                1 => assert_eq!(*value_mut, 33),
+                _ => panic!(),
+            }
+        }
+    }
+
 }

lib/entity/src/set.rs

@@ -55,7 +55,7 @@ where
 
     /// Iterate over all the keys in this set.
     pub fn keys(&self) -> Keys<K> {
-        Keys::new(self.len)
+        Keys::with_len(self.len)
     }
 
     /// Resize the set to have `n` entries by adding default entries as needed.