Implement empty iterator for types with no ast node children.

src/iter/macros.rs

@@ -0,0 +1,30 @@
+/// Create iterators for ast nodes where it only has to iterate over children
+macro_rules! simple_iter {
+    ($astnodetype:ty, $itertype:ident, $innertype:ty) => {
+        pub struct $itertype<'r, 's> {
+            next: $innertype,
+        }
+
+        impl<'r, 's> Iterator for $itertype<'r, 's> {
+            type Item = AstNode<'r, 's>;
+
+            fn next(&mut self) -> Option<Self::Item> {
+                self.next.next().map(Into::<AstNode>::into)
+            }
+        }
+
+        impl<'r, 's> IntoIterator for &'r $astnodetype {
+            type Item = AstNode<'r, 's>;
+
+            type IntoIter = $itertype<'r, 's>;
+
+            fn into_iter(self) -> Self::IntoIter {
+                $itertype {
+                    next: self.children.iter(),
+                }
+            }
+        }
+    };
+}
+
+pub(crate) use simple_iter;