Implement ExactSizeIterator for the other node types.

src/iter/macros.rs

@@ -11,8 +11,15 @@ macro_rules! children_iter {
             fn next(&mut self) -> Option<Self::Item> {
                 self.next.next().map(Into::<AstNode>::into)
             }
+
+            fn size_hint(&self) -> (usize, Option<usize>) {
+                let size = self.next.len();
+                (size, Some(size))
+            }
         }
 
+        impl<'r, 's> ExactSizeIterator for $itertype<'r, 's> {}
+
         impl<'r, 's> IntoIterator for &'r $astnodetype {
             type Item = AstNode<'r, 's>;
 
@@ -42,8 +49,14 @@ macro_rules! empty_iter {
             fn next(&mut self) -> Option<Self::Item> {
                 None
             }
+
+            fn size_hint(&self) -> (usize, Option<usize>) {
+                (0, Some(0))
+            }
         }
 
+        impl<'r, 's> ExactSizeIterator for $itertype<'r, 's> {}
+
         impl<'r, 's> IntoIterator for &'r $astnodetype {
             type Item = AstNode<'r, 's>;